Neutropenic fever is a medical emergency defined as a single oral temperature ≥38.3°C (or ≥38.0°C sustained over one hour) in a patient with an absolute neutrophil count < 500 cells/µL or expected to decline to that level, most commonly occurring after cytotoxic chemotherapy and requiring urgent empiric broad-spectrum antibiotic therapy.

Exam domain	One-glance essentials
Definition / diagnosis	*Fever: single oral temperature ≥38.3°C or ≥38.0°C sustained for ≥1 hour + ANC ≤0.5 × 10⁹/L, or ANC ≤1.0 × 10⁹/L expected to fall to ≤0.5 within 48 hours* ^[1] Suspected neutropenic sepsis is an acute medical emergency—an unwell patient after anticancer therapy needs immediate assessment and empiric treatment even if fever is blunted or no source is found ^[5]
Epidemiology / risks	*Infection/bacteraemia risk is driven chiefly by the depth and duration of neutropenia* ^[1]^[4] High risk: expected neutropenia > 7 days, septic/unstable presentation, major comorbidity or MASCC < 21; ANC < 0.1 × 10⁹/L is profound ^[6] Mucositis and central lines are important portals, but are not stronger predictors than depth/duration ^[1]
Core mechanism	*Cytotoxic therapy → marrow suppression + short neutrophil survival → loss of innate bacterial/fungal killing* ^[1] *Chemotherapy mucositis and catheter breaches → oral, gut or skin flora translocate → bacteraemia/fungaemia* ^[1] Longer neutropenia shifts the spectrum from bacteria → Candida → moulds (especially Aspergillus) ^[1]^[2]
Clinical picture	*Fever may be the only sign; steroids, chemotherapy and NSAIDs can blunt it* ^[1] *Inflammatory findings may be absent: little/no pus, consolidation, pyuria or CSF pleocytosis* ^[1] Search daily for oral mucositis, lung, abdominal/RIF, perianal, skin/CVC, biopsy-site and sinus clues; rigor or hypotension = sepsis until proved otherwise ^[1]
Investigations	Before antibiotics if this causes no delay: ≥2 blood-culture sets from separate sites; add cultures from each CVC lumen where present ^[6] *Immediate CBC/differential and renal/liver function; add lactate and repeat focused examination daily ^[1]^[5] Image by syndrome: CT chest* if high risk/respiratory features; CT abdomen for pain, tenderness or diarrhoea; test stool for C. difficile when diarrhoea is present ^[1]
Management	*After septic work-up, give empiric broad-spectrum anti-pseudomonal antibiotics immediately; initial dose within 1 hour of triage* ^[1]^[3]^[8] IV piperacillin–tazobactam, cefepime, imipenem or meropenem are accepted first-line options; select using severity, allergy, renal function, prior colonisation and the local antibiogram ^[5]^[6] Admit high-risk patients; outpatient oral therapy is only for carefully validated low-risk patients with reliable follow-up ^[6]^[8] Do not add vancomycin or an aminoglycoside routinely; reserve extra coverage for a clinical/microbiological indication or severe infection ^[5]^[6]
Complications	Fulminant Gram-negative sepsis → septic shock, DIC and multiorgan failure ^[1] RIF pain ± diarrhoea → neutropenic enterocolitis (typhlitis) with haemorrhage/perforation risk ^[1] Persistent fever with prolonged neutropenia ± pulmonary nodules/halo sign → invasive fungal disease, especially aspergillosis ^[1]^[6]
Prevention / follow-up	*Before immunosuppression: treat dental, sinus, urinary, perianal and skin foci; teach 24-hour fever reporting and emergency presentation ^[1]^[5] Primary G-CSF prophylaxis* when chemotherapy FN risk is approximately ≥20% (or lower-risk regimens plus major patient risk factors); it is not routine adjunctive treatment for established FN ^[7] Use antibacterial/antifungal/antiviral prophylaxis only for defined high-risk groups under local protocols; hand hygiene and exposure reduction remain essential ^[1]^[6]
Exam traps	Negative cultures do not exclude FN; many episodes remain microbiologically undocumented, so never await culture results before treatment ^[1]^[6] *Avoid digital rectal examination; mucosal trauma can seed bacteraemia ^[1] A normal CXR or absent pus/pyuria is falsely reassuring in neutropenia ^[1] Persistent fever alone is not a reason to reflexively switch antibacterials or add vancomycin; after 72–96 hours*, repeat diagnostics and assess for invasive fungal infection, using pre-emptive/empiric therapy according to risk and findings ^[5]^[6]

References

^[1] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf (definitions, pathogen spectrum, clinical approach, investigations, management and prevention) ^[2] Past papers: 2020 Fourth Summative Assessment MCQ paper.pdf (Q82, day-10 pathogen) ^[3] Past papers: 2022 Fourth Summative MCQ.pdf (Q75, initial management after septic work-up) ^[4] AOS material: AOS - Microbio.pdf (Q6, degree and duration of neutropenia) ^[5] NICE Clinical Guideline CG151: Neutropenic sepsis: prevention and management in people with cancer (recommendations 1.3.1.1–1.4.4.1) ^[6] Sandherr M, et al. 2024 update of the AGIHO guideline on diagnosis and empirical treatment of fever of unknown origin in adult neutropenic patients. Lancet Regional Health – Europe. 2025;51:101214. doi:10.1016/j.lanepe.2025.101214 ^[7] Gyawali B, et al. WBC Growth Factors: ASCO Guideline Update. Journal of Clinical Oncology. Published online February 25, 2026. PMID: 41740078 ^[8] ASCO/IDSA Clinical Practice Guideline Update: Outpatient Management of Fever and Neutropenia in Adults Treated for Malignancy (initial empiric antibacterial therapy within 1 hour; validated low-risk outpatient selection)

Neutropenic Fever

Neutropenic fever ("neutropenic" from Latin neuter = neither + Greek penia = poverty, i.e. poverty of neutrophils; "fever" from Latin febris = heat) is a medical emergency defined by the co-occurrence of fever in a patient who is neutropenic, most commonly as a complication of cytotoxic chemotherapy or haematological malignancy.

Formal Definitions

Neutropenic fever is defined as: ^[1]^[2]^[3]

Neutropenia: ANC ≤ 0.5 × 10⁹/L (500/µL), OR ANC ≤ 1.0 × 10⁹/L with a predicted decline to ≤ 0.5 × 10⁹/L within 24–48 hours

Fever: Single oral temperature ≥ 38.3°C, OR persistent temperature ≥ 38.0°C sustained over ≥ 1 hour

Grading of neutropenia ^[3]^[4]:

Grade	ANC Threshold	Clinical Significance
Neutropenia	≤ 1.5 × 10⁹/L (≤ 1500/µL)	Mild — low infection risk
Severe neutropenia	≤ 0.5 × 10⁹/L (≤ 500/µL)	Clinically significant; risk of infection rises sharply
Profound neutropenia	≤ 0.1 × 10⁹/L (≤ 100/µL)	Very high risk; highest mortality

How to Calculate ANC

ANC = Total WBC × (% Neutrophils + % Bands) / 100

For example, WBC 2.0 × 10⁹/L with 20% neutrophils and 5% bands → ANC = 2.0 × 0.25 = 0.5 × 10⁹/L = severe neutropenia.

Remarks on Temperature

Normal fever is defined by oral temperature > 37.6°C (Lecture notes) ^[3]. However, for neutropenic fever the IDSA thresholds (≥ 38.3°C single or ≥ 38.0°C sustained ≥ 1 h) are used because minor temperature fluctuations are common; the higher threshold avoids over-treating. That said, in immunocompromised patients, any temperature elevation should prompt clinical suspicion — these patients may be unable to mount a normal febrile response.

Neutropenic fever occurs in 10–50% of patients with solid tumours, but the risk is much higher in haematological malignancies ^[1]^[5]^[6]
It is one of the commonest haemato-oncological emergencies ^[2]
Mortality is approximately 11% overall, rising to ~50% if septic shock develops ^[5]
In Hong Kong, haematological malignancies (AML, ALL, lymphoma receiving intensive chemotherapy) and patients undergoing haematopoietic stem cell transplantation (HSCT) represent the highest-risk populations
Incidence per chemotherapy cycle varies by regimen intensity:
- Dose-dense or myeloablative regimens (e.g. induction for AML): virtually 100%
- Standard regimens for solid tumours (e.g. breast, lung): 10–20% per cycle without G-CSF prophylaxis

3. Risk Factors

Understanding the risk factors is critical for risk stratification, which guides whether a patient needs inpatient IV antibiotics vs. can be managed as outpatient.

Rate of fall of ANC — a precipitous drop is higher risk than a slow decline ^[5]
Absolute level of ANC — ANC < 0.5 × 10⁹/L is the threshold; ANC < 0.1 × 10⁹/L (profound) confers highest risk ^[5]
Duration of neutropenia ≥ 7 days — prolonged neutropenia dramatically increases the risk of invasive fungal infections ^[1]^[5]

Why does prolonged neutropenia matter so much? Because neutrophils are the first-line innate immune defence against bacteria and fungi. Once the marrow reserve is exhausted and the ANC remains low, the mucosal barriers (damaged by chemotherapy) become the only — and insufficient — defence. After ~7 days, fungi (which grow more slowly than bacteria) have enough time to invade tissue.

Number and dose of chemotherapy agents used ^[5]
Type of cancer: haematological malignancies, bone marrow transplant, advanced stage ^[5]
Obstructions (lymphatics, GI tract, urinary tract, biliary tract) — stasis promotes bacterial colonisation ^[5]
Presence of foreign bodies (indwelling venous catheters/Hickman lines, ureteric stents, biliary stents) — provide a surface for biofilm formation ^[5]

Advanced age ^[5]
Poor performance status ^[5]
Organ dysfunction (renal, hepatic) ^[5]
Pre-existing co-morbidities (diabetes mellitus, COPD, etc.)
Mucositis severity — chemotherapy damages rapidly dividing mucosal epithelium, breaking the gut barrier and allowing translocation of gut flora

High Yield – Risk Factors for Neutropenic Fever

"The degree and duration of neutropenia" is the single most important determinant of infection risk in the immunocompromised host ^[7].

4. Anatomy and Function: Why Neutrophils Are the Key Players

Neutrophils (from Latin neuter = neither, referring to their neutral staining with both acidic and basic dyes; Greek philos = loving) are the most abundant circulating white blood cells (40–70% of total WBC). They are the first responders of the innate immune system.

Neutrophil lifecycle:

Production: Bone marrow (myeloid stem cell → myeloblast → promyelocyte → myelocyte → metamyelocyte → band → mature segmented neutrophil). This takes ~10–14 days.
Bone marrow reserve: A large pool of mature neutrophils is stored in the marrow, ready for rapid release (this is why early in infection, the WCC can rise rapidly — it's releasing reserves).
Circulation: Mature neutrophils circulate for only ~2–3 days before undergoing apoptosis ^[1]. This very short lifespan explains why neutropenia develops so rapidly after chemotherapy.
Tissue migration: Neutrophils are recruited to infection sites by chemokines; they phagocytose and kill bacteria via oxidative burst (reactive oxygen species) and degranulation (proteases, defensins).

Neutrophil nadir usually occurs on Day 7–10 after chemotherapy when all marrow reserve is depleted ^[1]^[2]. This varies between agents — Taxanes (e.g. paclitaxel, docetaxel) cause earlier nadir at Day 4–5; post-bone marrow transplant nadir occurs around Day 21 ^[5].

The GI tract, oropharynx, and skin are the three main sources of infection in neutropenic patients. Under normal conditions:

The intestinal mucosa has a single layer of columnar epithelium with tight junctions, a mucus layer, secretory IgA, and commensal bacteria that competitively exclude pathogens
Chemotherapy (especially agents like cytarabine, methotrexate, 5-FU) destroys rapidly dividing mucosal cells → mucositis → breakdown of this barrier → bacterial translocation from the gut lumen into the bloodstream
Similarly, skin integrity is breached by indwelling catheters, bone marrow biopsy sites, and chemotherapy-induced dermatitis

The body's defence against infection can be conceptualized in layers ^[8]:

Layer	Component	Examples
Physical barriers	Skin, mucous membranes, cilia, gastric acid	Disrupted by chemotherapy-induced mucositis, catheters
Innate immunity	Neutrophils, macrophages, NK cells, complement	Neutropenia removes the most critical component
Adaptive immunity	T cells, B cells, immunoglobulins	Impaired by lymphocyte-depleting agents (fludarabine, alemtuzumab), steroids, anti-CD20

In neutropenic fever, the problem is primarily at the innate immunity level — neutrophils cannot be recruited to sites of infection, so bacteria multiply unchecked.

5. Aetiology

Key Principle

Pathogens can only be identified (culture-positive) in 20–30% of neutropenic fever episodes ^[1]^[5]. The majority are fever of unknown origin (FUO) or clinically documented infections (clinical site identified but no organism isolated). This is why empirical broad-spectrum antibiotics must be given immediately — you treat before you identify.

5.1 Bacterial Pathogens (Most Common Cause)

Bacteria are the most frequent causes of neutropenic fever ^[3]^[4].

Gram-positive bacteria have become the most common identified organisms due to the increased use of indwelling intravascular catheters ^[1]^[7]:

Organism	Source / Association	Pathophysiology
Coagulase-negative Staphylococci (e.g. S. epidermidis)	Most common organism identified overall ^[3]; associated with indwelling catheters	Forms biofilm on catheter surfaces; low virulence but persistent bacteraemia
S. aureus	Skin lesions, indwelling catheter, central line ^[1]	More virulent; can cause metastatic infections (e.g. endocarditis, osteomyelitis)
Viridans streptococci	Dental abscess, substantial mucosal damage from chemotherapy ^[1]	Oral commensals translocate through damaged mucosa; can cause viridans streptococcal shock syndrome
Enterococci (E. faecalis, E. faecium)	GI tract translocation, urinary tract	Intrinsically resistant to cephalosporins; VRE is a growing concern

Gram-negative bacilli were traditionally the commonest cause and remain associated with the most severe infections due to endotoxaemia ^[1]^[7]:

Organism	Source	Why It Matters
Pseudomonas aeruginosa	Environmental, hospital-acquired ^[1]^[2]^[7]	Associated with the most serious infections; produces exotoxins, forms biofilms; high mortality if not covered empirically
E. coli	GI tract translocation ^[2]^[7]	Most common Gram-negative isolate in many centres
Klebsiella spp.	GI tract, biliary	ESBL-producing strains increasing in HK
Other Enterobacterales	GI translocation	Includes Enterobacter, Serratia, Proteus

Why is Pseudomonas so dangerous? Pseudomonas produces endotoxin (LPS → TLR4 activation → cytokine storm → septic shock) and multiple virulence factors (exotoxin A, elastases, pyocyanin). In a neutropenic patient who cannot mount an immune response, Pseudomonas bacteraemia can progress to fulminant sepsis within hours. This is why anti-pseudomonal cover is mandatory in empirical regimens.

Fungal infections usually occur in haematological malignancies and prolonged neutropenia (> 7 days) ^[1]^[7]:

Organism	Type	Clinical Features
Candida spp.	Yeast	Oral thrush, oesophageal candidiasis, candidaemia; think of this with mucosal damage
Aspergillus spp.	Mould (filamentous fungus)	Invasive pulmonary aspergillosis — presents with persistent fever despite broad-spectrum antibiotics, pleuritic chest pain, haemoptysis; CT shows "halo sign" (ground-glass surrounding nodule) or "air-crescent sign"
Pneumocystis jirovecii (PCP)	Atypical fungus	More common with T-cell deficiency (steroids, HIV); diffuse bilateral ground-glass on CXR/CT
Mucorales (Mucormycosis)	Mould	Rhinocerebral or pulmonary; rapidly fatal; associated with uncontrolled DM, prolonged neutropenia

Why do fungi appear later? Fungi replicate more slowly than bacteria. The initial bacterial flora are kept in check by empirical antibiotics, but fungi are not covered by standard antibacterial agents. After ~7 days of neutropenia and broad-spectrum antibiotics, the normal competitive flora are eliminated, and fungi (which are already colonising mucosal surfaces) can invade.

Human herpesviruses are common in high-risk patients with chemotherapy-induced mucositis ^[3]^[4]:

Reactivation of HSV-1 and HSV-2 (herpes simplex) — painful oral/genital ulcers
Reactivation of VZV (varicella-zoster virus) — dermatomal vesicular rash (shingles) or disseminated in severe immunosuppression
Reactivation of CMV/EBV/HHV-6 — can occur as a result of immunosuppression or receipt of blood products/stem cells ^[3]^[4]
Respiratory viruses: Influenza, parainfluenza, adenovirus, RSV — documented with increasing frequency ^[3]^[4]; important in HK during winter influenza season

Tuberculosis (TB): In HK (an endemic area for TB), extrapulmonary TB should be considered ^[5]; may present atypically
Parasitic: Strongyloides hyperinfection in patients from endemic areas receiving steroids

Most infections come from the GI tract, aerodigestive tract, and skin (from catheter) ^[1]:

6. Pathophysiology

Understanding the pathophysiology of neutropenic fever requires integrating the concepts of chemotherapy-induced marrow suppression, mucosal barrier breakdown, and impaired immune surveillance.

Step-by-step explanation:

Chemotherapy targets rapidly dividing cells — this includes both malignant cells and normal haematopoietic progenitors in the bone marrow. Neutrophil precursors (myeloblasts, promyelocytes) are destroyed.
Neutrophil lifespan is only ~2–3 days ^[1], so the circulating neutrophils die off quickly. Initially, the bone marrow reserve compensates. By Day 7–10, both circulating and reserve neutrophils are depleted → nadir.
Simultaneously, chemotherapy damages the mucosal epithelium of the GI tract (which also turns over rapidly, every 3–5 days). This causes mucositis — the mucosal barrier becomes ulcerated and permeable.
Commensal bacteria (E. coli, Klebsiella from the gut; viridans streptococci from the mouth; S. epidermidis from the skin around catheters) now have a portal of entry into the bloodstream.
Without neutrophils to phagocytose and kill these organisms, they proliferate unchecked in the blood → bacteraemia.
Fever is triggered by: (a) bacterial products (e.g. LPS from Gram-negative bacteria) acting as exogenous pyrogens; (b) endogenous pyrogens (IL-1, IL-6, TNF-α) released from residual macrophages and monocytes → these act on the hypothalamic thermoregulatory centre via prostaglandin E2 → raise the temperature set point.
If the bacteria are Gram-negative (especially Pseudomonas), their endotoxin (LPS) can trigger a massive inflammatory cascade → vasodilation, capillary leak, DIC → septic shock → death within hours if untreated.

Clinical features may be subtle due to diminished inflammatory response associated with myelosuppression ^[1]

This is a critically important concept. The classical signs of infection (redness, swelling, warmth, pus formation) all require neutrophil recruitment:

Redness and warmth = vasodilation from inflammatory mediators → partly present (macrophages can still release cytokines) but attenuated
Swelling = fluid exudation → partly present
Pus = collection of dead neutrophils → absent because there are no neutrophils to form pus ^[4]
Consolidation on CXR in pneumonia may be absent because radiographic infiltrates require inflammatory cell infiltration of the alveoli ^[5]

Therefore, fever is often the only presenting sign ^[1]. You cannot rely on the usual clinical features to diagnose infection. You must treat empirically.

7. Classification

Risk stratification determines the intensity of management:

Feature	High Risk	Low Risk
Duration of neutropenia	Anticipated ≥ 7 days	Expected ≤ 7 days
Depth of neutropenia	ANC < 0.1 × 10⁹/L (profound)	ANC 0.1–0.5
Comorbidities	Haemodynamically unstable, deranged LRFT, altered mental state	None significant
Cancer type	Haematological malignancy, HSCT	Solid tumour
MASCC score	< 21	≥ 21
Management	Inpatient IV antibiotics	Outpatient oral antibiotics (seldom done in HK) ^[5]

MASCC (Multinational Association for Supportive Care in Cancer) Risk Index Score:

Characteristic	Weight
Burden of illness: no or mild symptoms	5
Burden of illness: moderate symptoms	3
No hypotension (SBP ≥ 90)	5
No COPD	4
Solid tumour or no previous fungal infection	4
No dehydration requiring IV fluids	3
Outpatient at onset of fever	3
Age < 60 years	2
Maximum score	26

MASCC score ≥ 21 → Low risk (positive predictive value ~91%) MASCC score < 21 → High risk

HK Practice

In Hong Kong, low-risk outpatient management is seldom practised ^[5]. Most neutropenic fever patients are admitted for inpatient IV antibiotics, partly because of the high density of hospital care and ease of access. However, the MASCC score is still tested in exams.

Neutropenic fever episodes are classified based on whether an organism or site is identified:

Category	Definition	Frequency
Microbiologically documented infection (MDI)	Pathogen identified by culture + clinical infection	~20–30%
Clinically documented infection (CDI)	Clinical site of infection identified (e.g. pneumonia on CXR) but no organism isolated	~20–30%
Fever of unknown origin (FUO)	No site or organism identified despite workup	~50%

8. Clinical Features

Cardinal Rule

Signs of inflammation can be extremely subtle in the absence of neutrophils. Pus is NOT found due to lack of neutrophils ^[4]. Do not expect the classical features of infection. A neutropenic patient who "looks well" may be hours away from septic shock. Treat the fever, not the appearance.

Symptom	Pathophysiological Basis	Notes
Fever	Exogenous pyrogens (bacterial products like LPS) and endogenous pyrogens (IL-1, IL-6, TNF-α from residual macrophages) → hypothalamic PGE₂ → raised temperature set point	Often the ONLY presenting symptom ^[1]. May be blunted by steroids, NSAIDs, or antipyretics
Rigors / chills	Muscle contraction to generate heat when hypothalamic set point is raised; especially associated with bacteraemia (particularly Gram-negative)	Presence of rigors increases suspicion of blood-stream infection
Sore throat / dysphagia	Oral mucositis from chemotherapy → breakdown of oral mucosal barrier → secondary infection by oral flora (Candida, HSV, viridans streptococci)	Ask specifically; look for white plaques (Candida) or vesicles (HSV)
Cough / dyspnoea	Pneumonia — but CXR infiltrates may be absent ^[5] due to inability to mount inflammatory exudate; or may be present with atypical organisms	Consider bacterial, fungal (Aspergillus), viral (RSV, influenza), PCP
Abdominal pain / diarrhoea	Neutropenic enterocolitis (typhlitis) — inflammation and necrosis of the caecum/ascending colon; or C. difficile colitis from antibiotic exposure	Abdominal pain + diarrhoea in a neutropenic patient = typhlitis until proven otherwise
Perianal pain	Perianal abscess/cellulitis — but without pus formation; the perianal area is rich in bacteria from the GI tract and is a common entry site	Avoid digital rectal examination (DRE) as it can traumatise fragile mucosa and introduce infection ^[4]
Skin lesions / rash	May indicate disseminated infection (e.g. ecthyma gangrenosum from Pseudomonas — necrotic skin lesion), HSV vesicles, VZV dermatomal rash	Any new skin lesion in a neutropenic patient should be biopsied and cultured
Catheter site pain / redness	Line sepsis — biofilm on catheter surface → bacteraemia	Always inspect catheter exit sites
Decreased oral intake / mental obtundation	Suggests sepsis ^[4] — hypoperfusion of CNS, metabolic derangement	A subtle sign that should prompt escalation
Urinary symptoms (dysuria, frequency)	UTI — less common source but still possible, especially with urinary catheters	May be masked; pyuria may be absent (no neutrophils to produce WBCs in urine)

Full history and physical examination (done daily) should focus on: ^[9]

Site to Examine	What to Look For	Pathophysiological Basis
Skin	Erythema, cellulitis, ecthyma gangrenosum (black necrotic lesions — pathognomonic for Pseudomonas), herpetic vesicles, catheter exit site erythema	Skin is a major portal of entry; necrotic lesions occur because neutrophils cannot wall off infection
Oral cavity	Mucositis (erythema, ulceration), white plaques (Candida), vesicles (HSV), dental abscess	Chemotherapy damages oral epithelium; oral flora (viridans streptococci, Candida) invade
Lungs	Crackles, reduced breath sounds, dullness to percussion	Pneumonia — but auscultatory findings may be minimal without neutrophilic inflammation
Abdomen	Abdominal tenderness, peritoneal signs → may represent neutropenic enterocolitis or C. difficile colitis ^[4]	Caecal inflammation ± necrosis; can perforate
Perianal area	Erythema, pain, tender haemorrhoids suggesting infection ^[4]	DO NOT perform DRE
IV catheter sites / Hickman exit site	Erythema and tenderness suggesting infection; MUST exclude line sepsis ^[4]^[9]	Biofilm-associated infection
BM biopsy site	Erythema, tenderness, discharge	Recent procedural wound — portal of entry
Nasal sinuses	Tenderness over sinuses, nasal discharge, facial pain	Fungal sinusitis (Aspergillus, Mucor) in prolonged neutropenia ^[9]
Vital signs	BP, Pulse, Temperature, RR, SpO₂, GCS ^[4]	Haemodynamic instability suggests sepsis/septic shock
General appearance	Ill-looking, mental obtundation, decreased oral intake ^[4]	Suggests systemic sepsis

"Full Hx & P/E (daily): skin, oral, lung, abdomen, perianal, Hickman exit, BM Bx site; over nasal sinus" ^[9]

8.3 Special Clinical Scenarios

"Typhlitis" from Greek typhlon = caecum
Necrotising inflammation of the caecum (and sometimes other parts of the colon) occurring in neutropenic patients
Pathogenesis: chemotherapy → mucosal damage to caecal wall + neutropenia → invasion by gut bacteria → transmural inflammation ± necrosis ± perforation
Why the caecum? The caecum has the thinnest wall and poorest blood supply of the large bowel, making it most vulnerable
Clinical features: RIF pain, diarrhoea (may be bloody), fever, abdominal distension
Diagnosis: CT abdomen showing caecal wall thickening, pericolonic fat stranding ± pneumatosis
Complications: perforation, peritonitis, septic shock — surgical emergency

Pathognomonic skin lesion of Pseudomonas aeruginosa bacteraemia
Begins as painless red macule → rapidly progresses to haemorrhagic bulla → central black necrotic eschar with erythematous halo
Pathogenesis: Pseudomonas invades blood vessel walls (vasculitis) → thrombosis → ischaemic necrosis of overlying skin
May occur at any site but commonly in perineum, axilla, or extremities

Before we discuss investigations and management (which will be covered in the next response), it is important to understand the clinical approach:

The key principle: neutropenic fever is a medical emergency because unchecked proliferation of bacteria can lead to rapid progression into septic shock, especially in Gram-negative sepsis ^[1]. Empirical antibiotics must be started ASAP after immediate septic workup — ideally < 1–2 hours after presentation ^[1].

Neutropenic Card

Patients receiving chemotherapy are given a "neutropenic card" — they are taught to present this card to any healthcare provider if they develop fever, so that empirical antibiotics can be started immediately without delay ^[2].

Principle	Explanation
Why is fever often the only sign?	Neutrophils are required for pus formation, tissue erythema/swelling, and CXR consolidation. Without neutrophils, these classical signs are absent.
Why cover Pseudomonas empirically?	Pseudomonas causes the most fulminant sepsis via endotoxin; mortality without adequate cover is extremely high.
Why do fungal infections occur after 7 days?	Fungi grow slowly; they emerge when prolonged neutropenia + broad-spectrum antibiotics eliminate competing bacteria.
Why is the GI tract the main source?	Chemotherapy causes mucositis → breaks the mucosal barrier → allows translocation of gut bacteria into the bloodstream.
Why has Gram-positive become more common?	Increased use of indwelling catheters (Hickman lines, PICCs) provides a surface for biofilm formation by skin commensals (CoNS, S. aureus).
Why does nadir occur at Day 7–10?	Neutrophil lifespan is ~2–3 days. After chemotherapy kills the progenitors, the marrow reserve sustains levels for a few more days before being exhausted.

High Yield Summary

Definition:

Neutropenic fever = ANC ≤ 0.5 × 10⁹/L (or ≤ 1.0 with predicted decline to ≤ 0.5 in 48h) + single oral temp ≥ 38.3°C or sustained ≥ 38.0°C for ≥ 1 hour

Key Numbers:

Occurs in 10–50% of solid tumours; higher in haematological malignancies
Only 20–30% are culture-positive
Mortality ~11% overall, ~50% with septic shock
Nadir: Day 7–10 (Taxanes D4–5; post-HSCT D21)
Neutrophil lifespan: ~2–3 days

Risk Factors: Duration and depth of neutropenia are most important; prolonged ( ≥ 7 days) and profound ( < 0.1) = highest risk

Pathogens:

Gram-positive now most common (CoNS, S. aureus, viridans strep) — due to catheters
Gram-negative most dangerous (Pseudomonas, E. coli) — endotoxin → septic shock
Fungal (Candida, Aspergillus) — with prolonged neutropenia > 7 days
Viral reactivation (HSV, VZV, CMV)

Clinical Features:

Fever is often the ONLY sign
Pus is NOT formed (no neutrophils)
CXR may be normal despite pneumonia
Examine: skin, oral cavity, lungs, abdomen, perianal area, catheter sites, BM biopsy sites, sinuses — DAILY
Avoid DRE

Principle: Medical emergency — start empirical broad-spectrum anti-pseudomonal antibiotics within 1 hour of presentation

Active Recall - Neutropenic Fever (Definition, Epidemiology, Aetiology, Pathophysiology, Clinical Features)

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 423, Complications of Leukemia — Neutropenic Fever) ^[2] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p. 11, Haematological Emergencies — Neutropenic fever) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 1329–1331, Neutropenic fever) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 572–574, Neutropenic fever) ^[5] Senior notes: Maksim Medicine Notes.pdf (p. 49, Clinical oncology — Neutropenic fever) ^[6] Senior notes: Ryan Ho Haemtology.pdf (p. 70, Complications of Leukaemia — Neutropenic Fever) ^[7] AOS material: AOS - Microbio.pdf (p. 5, Neutropenic fever pathogens) ^[8] Lecture slides: GC 100. Defense against microbes.pdf ^[9] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf (p. 8, Approach to Mx of neutropenic fever)

Differential Diagnosis of Neutropenic Fever

When a patient on chemotherapy (or with known haematological malignancy) presents with fever and neutropenia, the immediate clinical reflex is to treat for infection empirically. However, a systematic differential diagnosis is still essential for two reasons:

Not all fevers in neutropenic patients are infectious — non-infectious causes must be considered, especially if fever persists despite broad-spectrum antibiotics.
Among infectious causes, identifying the site and organism changes the antibiotic/antifungal strategy and duration.

The differential diagnosis of neutropenic fever is really two questions running in parallel:

Question 1: Is this fever due to infection, or is there a non-infectious cause?

Question 2: If infectious, where is the source and what is the organism?

Pathogens can only be identified in 20–30% of neutropenic fever episodes ^[1]^[6]. The remainder are either clinically documented infections (a site is found but no organism isolated) or fever of unknown origin (~50%) ^[5]. This makes the differential diagnosis a process of active exclusion rather than definitive identification.

I. Infectious Causes (The Primary Concern)

This is the most important category. In a neutropenic patient, you must assume infection until proven otherwise and treat empirically, because delay kills.

A. Bacterial Infections

Bacteria are the most frequent causes of neutropenic fever ^[3]^[4].

Gram-positive bacteria have become the most common identified organisms with increased use of indwelling intravascular catheters ^[1]^[2]^[7].

Organism	Typical Source / Clue	Why It Matters
Coagulase-negative Staphylococci (CoNS, e.g. S. epidermidis)	Most common organism identified overall ^[3]^[4]; indwelling CVC / Hickman line	Low virulence but persistent; forms biofilm on catheter → line sepsis; may be dismissed as contaminant (need ≥ 2 positive cultures from different sites to confirm)
S. aureus	Skin lesions, indwelling catheter, central line ^[1]	Higher virulence; metastatic complications (endocarditis, osteomyelitis, septic arthritis); always significant when isolated
Viridans group streptococci	Dental abscess, chemotherapy-induced oral mucositis ^[1]	Can cause viridans streptococcal shock syndrome (especially with high-dose cytarabine); ~10% mortality
Enterococci (E. faecalis, E. faecium)	GI translocation, urinary tract, intra-abdominal	Intrinsically resistant to cephalosporins; VRE (vancomycin-resistant enterococci) emerging in HK
Streptococcus pneumoniae	Respiratory tract	More common in patients with very low immunoglobulin levels (hypogammaglobulinaemia) ^[7]

Line Sepsis — Always Consider

MUST exclude line sepsis in any neutropenic patient with a central venous catheter ^[3]^[4]^[9]. A patient with fever + erythema/tenderness at the Hickman exit site has line sepsis until proven otherwise. Blood cultures should be drawn from both the CVC (through two different ports) and from a peripheral venous puncture ^[9] — differential time to positivity (DTTP) ≥ 2 hours earlier from the CVC line suggests catheter-related bloodstream infection.

Gram-negative bacilli were traditionally the commonest organisms and remain associated with the most severe infections due to endotoxaemia ^[1]^[2]^[7].

Organism	Typical Source / Clue	Why It Matters
E. coli	GI tract translocation ^[2]^[7]	Most common Gram-negative isolate in many centres; can produce ESBL (extended-spectrum beta-lactamases) — increasingly common in HK
Pseudomonas aeruginosa	Hospital-acquired, environmental ^[1]^[2]^[7]	Associated with the most serious infection ^[1]; ecthyma gangrenosum (pathognomonic necrotic skin lesion); high mortality if inadequate cover
Klebsiella spp.	GI tract, biliary	ESBL-producing and carbapenem-resistant strains increasing globally and in HK
Enterobacter, Serratia, Proteus	GI translocation, nosocomial	May demonstrate inducible AmpC resistance → can appear susceptible initially but develop resistance on cephalosporins

Why is Gram-negative sepsis so feared? The lipopolysaccharide (LPS / endotoxin) in the Gram-negative outer membrane is a potent activator of TLR4 on macrophages → massive release of TNF-α, IL-1β, IL-6 → systemic inflammatory response → vasodilatory shock, DIC, multi-organ failure. Without neutrophils to contain the infection early, this cascade can become irreversible within hours.

Organism	Typical Source / Clue	Why It Matters
Clostridium difficile	Antibiotic-associated diarrhoea — prior broad-spectrum antibiotics disrupt colonic flora	Diagnose by stool C. difficile cytotoxin assay or PCR ^[3]^[4]^[9]; treatment: oral vancomycin or fidaxomicin
Bacteroides fragilis	Intra-abdominal / perianal sepsis	Should be considered in patients with abdominal/perianal symptoms
Fusobacterium	Oropharyngeal source, dental infection	Lemierre syndrome (internal jugular vein thrombophlebitis) — rare but notable

Mycobacterium tuberculosis: In Hong Kong (endemic area), extrapulmonary TB should always be considered ^[5], especially with prolonged fever unresponsive to antibiotics. May present atypically — miliary pattern, hepatic/splenic involvement, bone marrow infiltration
Atypical mycobacteria (NTM, e.g. M. avium complex): In severely immunosuppressed (especially post-HSCT, HIV co-infection)
Nocardia: Filamentous Gram-positive rod; presents with pulmonary nodules, brain abscess, skin lesions; consider in patients on prolonged steroids

Fungal infections usually occur in haematological malignancies and prolonged neutropenia (> 7 days) ^[1]^[7]. They are the second most important category after bacteria and typically emerge when initial antibacterial therapy has failed.

Organism	Type	Clinical Clue / Source	Key Diagnostic Feature
Candida spp.	Yeast ^[7]	Oral thrush (white plaques), oesophageal candidiasis (odynophagia), candidaemia (persistent fever despite antibiotics + CVC in situ)	Blood culture (but sensitivity only ~50%); serum β-D-glucan
Aspergillus spp.	Mould ^[7]	Persistent fever despite broad-spectrum antibiotics > 4–7 days; pleuritic chest pain, haemoptysis; pulmonary nodules	CT thorax: "halo sign" (ground-glass halo around nodule), later "air-crescent sign"; serum galactomannan ^[9]; BAL culture/galactomannan
Pneumocystis jirovecii (PCP/PJP)	Atypical fungus ^[5]^[10]	Progressive dyspnoea, dry cough, hypoxia; bilateral ground-glass opacities on CXR/CT; ↑LDH, ↑β-D-glucan ^[10]	Induced sputum or BAL for silver stain/IF/PCR; cannot be cultured ^[10]
Mucorales (Rhizopus, Mucor)	Mould	Rhinocerebral (facial pain, necrotic eschar on palate/nasal mucosa) or pulmonary; associated with uncontrolled DM, prolonged neutropenia	Tissue biopsy showing broad, non-septate, ribbon-like hyphae with 90° branching
Talaromyces (Penicillium) marneffei	Dimorphic fungus	Important in Southern China / HK and Southeast Asia; associated with advanced HIV; disseminated disease with skin papules with central umbilication, hepatosplenomegaly	Blood/tissue culture; histology showing intracellular yeast with central septum

Serial serum galactomannan and 1,3 β-D-glucan testing is part of the monitoring strategy in high-risk neutropenic patients ^[9].

When to Suspect Fungal Infection

Think of invasive fungal infection when:

Fever persists > 4–7 days despite adequate broad-spectrum antibiotics
Neutropenia is prolonged (≥ 7 days) or profound (ANC < 0.1)
Patient has a haematological malignancy or is post-HSCT
New pulmonary nodules or sinus symptoms develop

Human herpesviruses are common in high-risk patients with chemotherapy-induced mucositis ^[3]^[4]:

Virus	Mechanism	Clinical Clue
HSV-1 / HSV-2	Reactivation in setting of immunosuppression + mucosal damage	Painful oral/labial vesicles/ulcers; genital lesions; may disseminate
VZV	Reactivation (prior varicella)	Dermatomal vesicular rash (shingles); can disseminate with multi-dermatomal or visceral involvement
CMV	Reactivation especially post-HSCT, post solid-organ transplant	Colitis (bloody diarrhoea), pneumonitis, retinitis; diagnose by CMV PCR (viral load)
EBV / HHV-6	Reactivation due to immunosuppression or receipt of blood products/stem cells ^[3]^[4]	EBV: PTLD (post-transplant lymphoproliferative disorder); HHV-6: encephalitis post-HSCT
Respiratory viruses (Influenza, parainfluenza, RSV, adenovirus)	Documented with increasing frequency ^[3]^[4]	Coryza, cough, rhinorrhoea; can cause severe pneumonia in immunocompromised; multiplex PCR (NPA) for diagnosis

Why viral reactivation? During chemotherapy, cytotoxic T-lymphocytes (which keep latent herpesviruses in check) are depleted. When immune surveillance drops, latent virus in sensory ganglia (VZV, HSV) or lymphocytes (EBV, CMV) reactivates and begins replicating.

Pathogen	Clinical Context	Notes
Mycobacterium tuberculosis	Endemic in HK; extrapulmonary presentations common ^[5]	Disseminated / miliary TB; consider if prolonged FUO
Toxoplasma gondii	Post-HSCT, HIV	Brain abscess with ring-enhancing lesions
Strongyloides stercoralis	Patient from endemic area (SE Asia) receiving steroids	Hyperinfection syndrome with Gram-negative bacteraemia due to larvae carrying gut bacteria through bowel wall

II. Non-Infectious Causes of Fever in Neutropenic Patients

These are important to consider, especially when fever persists despite appropriate empirical antimicrobials and all cultures remain negative. Non-infectious causes account for an estimated 30–40% of febrile episodes in neutropenic patients.

Mechanism	Culprits	Clinical Clue
Hypersensitivity reaction, direct pyrogenicity, or altered thermoregulation	Cytarabine (Ara-C), bleomycin, amphotericin B, G-CSF, biological agents (rituximab, alemtuzumab), antibiotics (β-lactams, vancomycin), allopurinol	Temporal correlation with drug administration; "looks well" despite fever; may have eosinophilia or rash; resolves when offending drug is discontinued

Why does G-CSF cause fever? G-CSF (granulocyte colony-stimulating factor) stimulates neutrophil production and release from the bone marrow. This process involves bone marrow expansion (→ bone pain) and release of pyrogenic cytokines (IL-6, TNF-α) from activated marrow cells → fever. This is a common clinical conundrum: the drug given to treat neutropenia itself causes fever, mimicking infection.

Mechanism	Clinical Clue
Tumour cells produce endogenous pyrogens (IL-1, IL-6, TNF-α) directly, or tumour necrosis releases pyrogens	More common in haematological malignancies (lymphoma, leukaemia) than solid tumours; may be the initial presentation of relapsed/refractory disease; diagnosed by exclusion; classically responds to naproxen test (fever resolves with naproxen 250 mg BD for 3 days — "Naproxen test positive")

Fever during or after transfusion requires consideration of three main differentials ^[11]:

Type	Mechanism	Key Distinction
Febrile non-haemolytic transfusion reaction (FNHTR)	Most common cause; cytokines released from residual leucocytes in blood products act as pyrogens	Fever is NOT a contraindication for continuing transfusion if FNHTR confirmed ^[11]; exclude ABO incompatibility and bacterial contamination first
ABO incompatibility (acute haemolytic transfusion reaction)	Anti-A or anti-B antibodies attack transfused RBCs → intravascular haemolysis → massive cytokine release	Fever + rigors + flank pain + dark urine + hypotension → stop transfusion immediately
Bacterial contamination of blood products	Bacteria (especially in platelets stored at room temperature) release endotoxin	High fever, rigors, hypotension shortly after starting transfusion → stop immediately, culture the bag

Context	Mechanism	Clinical Clue
Post-allogeneic HSCT; or after non-irradiated blood product transfusion (transfusion-associated GVHD)	Donor T-lymphocytes attack recipient tissues	Fever + skin rash (maculopapular, may be extensive) + diarrhoea + liver dysfunction (↑bilirubin, ↑ALP); usually occurs Day 14–45 post-HSCT for acute GVHD

Mechanism	Clinical Clue
Cancer patients are hypercoagulable (Virchow's triad: stasis from immobility, endothelial injury from CVC, hypercoagulability from malignancy); DVT/PE releases tissue factor and pyrogens	Unilateral leg swelling (DVT); pleuritic chest pain, dyspnoea, tachycardia (PE); fever is typically low-grade

Mechanism	Clinical Clue
Chronic steroid use (common in haem-onc regimens, e.g. dexamethasone in lymphoma/myeloma) → HPA axis suppression → adrenal crisis when steroids are abruptly withdrawn or during physiological stress	Hypotension refractory to fluids, hypoglycaemia, hyponatraemia, hyperkalaemia, fever; responds to IV hydrocortisone

Mucositis itself — severe mucosal inflammation can release cytokines and cause low-grade fever even without superinfection
Engraftment syndrome — post-HSCT, when neutrophils begin to recover, the engraftment process itself can cause fever, rash, and non-cardiogenic pulmonary oedema (typically around Day 10–14 post-transplant)
Haemophagocytic lymphohistiocytosis (HLH) / Macrophage activation syndrome — a life-threatening hyperinflammatory condition triggered by infections (especially EBV, CMV), malignancy, or drugs; presents with high fever, cytopenias, hyperferritinaemia (often > 10,000), hypertriglyceridaemia, hepatosplenomegaly

A practical approach is to think about the differential by site, as emphasised in the clinical examination:

Full Hx & P/E (daily): skin, oral, lung, abdomen, perianal, Hickman exit, BM Bx site; over nasal sinus ^[9]

Site	Infectious DDx	Non-Infectious DDx
Skin / Catheter sites ^[9]	Cellulitis (S. aureus, streptococci), line sepsis (CoNS, S. aureus), ecthyma gangrenosum (Pseudomonas), HSV/VZV vesicles, fungal skin lesions	Drug rash, GVHD rash, Sweet syndrome (acute febrile neutrophilic dermatosis — paradoxically can occur even in neutropenia)
Oral cavity ^[9]	Oral candidiasis (thrush), HSV stomatitis, viridans streptococcal mucositis, dental abscess, necrotising gingivitis	Chemotherapy-induced mucositis (sterile)
Lungs ^[9]	Bacterial pneumonia (Gram-negative, Gram-positive), Aspergillus (persistent fever + nodules), PJP (bilateral GGO), CMV pneumonitis, respiratory viruses, TB	Drug-induced pneumonitis (e.g. bleomycin, methotrexate), radiation pneumonitis, pulmonary haemorrhage (thrombocytopaenia), pulmonary embolism, engraftment syndrome
Abdomen ^[9]	Neutropenic enterocolitis (typhlitis), C. difficile colitis, hepatosplenic candidiasis, cholangitis, appendicitis (may lack classical signs)	Tumour-related pain, ileus, pancreatitis (asparaginase)
Perianal area ^[9]	Perianal abscess/cellulitis (without pus formation), perianal fissure/fistula with superinfection	Haemorrhoids
Nasal sinuses ^[9]	Fungal sinusitis (Aspergillus, Mucor) — especially with prolonged neutropenia	Allergic sinusitis
BM biopsy site ^[9]	Wound infection, cellulitis	Haematoma
CNS	Bacterial meningitis, viral encephalitis (HSV, HHV-6), fungal meningitis (Cryptococcus), Toxoplasma brain abscess	Leukaemic / lymphomatous CNS infiltration, drug toxicity (e.g. methotrexate leukoencephalopathy)
Urinary tract	UTI (E. coli, Klebsiella, Enterococcus, Candida) — note that pyuria may be absent in neutropenia	Obstructive uropathy from tumour

The timing of fever relative to the chemotherapy cycle and duration of neutropenia helps narrow the differential:

Timing	Most Likely Pathogens	Rationale
Day 0–7 post-chemo	Drug fever, mucositis (sterile), early bacterial infection from pre-existing colonisation	Neutrophil count may still be adequate; mucositis developing
Day 7–14 post-chemo (nadir) ^[1]^[2]	Gram-positive bacteraemia (line sepsis), Gram-negative bacteraemia (GI translocation)	ANC at its lowest; mucosal barrier maximally damaged
> 7 days of neutropenia	Invasive fungal infection (Candida, Aspergillus) ^[1]^[7]	Fungi are slow-growing; emerge when bacteria are suppressed by antibiotics and neutropenia is prolonged
> 14 days of neutropenia	Moulds (Aspergillus, Mucor), viral reactivation (CMV, HHV-6)	Very prolonged immunosuppression; typically post-HSCT patients
Neutrophil recovery phase	Engraftment syndrome, "unmasking" of previously subclinical infection (e.g. hepatosplenic candidiasis becomes apparent as neutrophils return and mount an inflammatory response)	Paradoxical clinical deterioration as immune reconstitution reveals occult infections

Feature	Favours Infection	Favours Non-Infectious
Rigors / chills	Present (especially bacteraemia)	Absent or mild
Haemodynamic instability	Present in sepsis	Usually stable (except PE, adrenal crisis)
Localising signs	Present if site identified (though may be subtle)	Absent
Response to empirical antibiotics	Fever resolves within 48–72 h	Fever persists despite adequate antibiotics
Temporal relation to drug administration	No specific pattern	Fever onset correlates with drug timing
CRP / Procalcitonin trend	Rising or very high	May be elevated but stable or falling
Blood cultures	Positive in ~20–30%	Negative
Naproxen test	Negative (fever persists)	Positive (fever resolves — suggests tumour fever)

High Yield — Persistent Fever Despite Antibiotics

If a neutropenic patient remains febrile after 4–7 days of adequate empirical antibacterial therapy, think about:

Invasive fungal infection (Aspergillus, Candida) — most important
Resistant organism not covered by current regimen
Drug fever from the antibiotic itself
Non-infectious cause (tumour fever, GVHD, VTE)
Abscess / collection that requires drainage (CT-guided or surgical)
Viral infection (CMV, HHV-6 reactivation)

Category	Specific Causes	Key Clinical Clue
Gram-positive bacteria	CoNS, S. aureus, viridans strep, enterococci	CVC in situ, oral mucositis, skin breakdown
Gram-negative bacteria	E. coli, Pseudomonas, Klebsiella	GI translocation, ecthyma gangrenosum, endotoxic shock
Anaerobes	C. difficile, Bacteroides	Diarrhoea, abdominal pain, recent antibiotics
Fungi	Candida, Aspergillus, PJP, Mucor	Prolonged neutropenia > 7d, persistent fever, pulmonary nodules
Viruses	HSV, VZV, CMV, respiratory viruses	Vesicular lesions, reactivation in immunosuppressed, coryza
Mycobacteria	TB (extrapulmonary in HK)	Prolonged FUO, endemic area, disseminated disease
Drug fever	Cytarabine, G-CSF, antibiotics	Temporal correlation, "looks well," eosinophilia
Tumour fever	Leukaemia/lymphoma	Positive naproxen test, diagnosis of exclusion
Transfusion reaction	FNHTR, ABO incompatibility, bacterial contamination	Temporal relation to blood product administration
GVHD	Post-allogeneic HSCT	Rash + diarrhoea + liver dysfunction
VTE (DVT/PE)	Cancer hypercoagulability	Leg swelling, pleuritic pain, tachycardia
Engraftment syndrome	Neutrophil recovery post-HSCT	Fever + rash + pulmonary oedema at count recovery
HLH/MAS	Triggered by EBV, malignancy	Hyperferritinaemia, hypertriglyceridaemia, pancytopenia

High Yield Summary — Differential Diagnosis of Neutropenic Fever

Primary concern is always INFECTION — treat empirically before the pathogen is identified.

Infectious causes:

Bacteria are most common; Gram-positive now more frequent (catheter-related), but Gram-negative most dangerous (endotoxic shock)
Fungi emerge with prolonged neutropenia > 7 days (Aspergillus, Candida)
Viruses — herpesvirus reactivation (HSV, VZV, CMV) and respiratory viruses
TB — always consider in HK (endemic); extrapulmonary presentations

Non-infectious causes (consider when fever persists despite adequate antibiotics):

Drug fever (temporal correlation, "looks well")
Tumour fever (positive naproxen test)
Transfusion reaction (exclude ABO incompatibility first)
GVHD (post-HSCT: rash + diarrhoea + liver dysfunction)
VTE / PE
Engraftment syndrome

Clinical approach by site: Examine skin, oral cavity, lungs, abdomen, perianal area, catheter sites, BM biopsy sites, and sinuses — DAILY

Temporal pattern: Day 7–14 = bacteria at nadir; > 7 days neutropenia = fungi; recovery phase = engraftment syndrome / unmasking

Active Recall - Differential Diagnosis of Neutropenic Fever

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 423, Complications of Leukemia — Neutropenic Fever) ^[2] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p. 11, Haematological Emergencies — Neutropenic fever) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 1329–1333, Neutropenic fever) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 572–574, 745, Neutropenic fever) ^[5] Senior notes: Maksim Medicine Notes.pdf (p. 49, Clinical oncology — Neutropenic fever) ^[6] Senior notes: Ryan Ho Haemtology.pdf (p. 70, Complications of Leukaemia — Neutropenic Fever) ^[7] AOS material: AOS - Microbio.pdf (p. 5, Neutropenic fever pathogens) ^[9] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf (p. 8, Approach to Mx of neutropenic fever) ^[10] Senior notes: Ryan Ho Respiratory.pdf (p. 69, Pneumocystis Jirovecii Pneumonia) ^[11] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (p. 5, 8, Adverse effects of transfusion)

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Neutropenic Fever

I. Diagnostic Criteria

Neutropenic fever is a clinical diagnosis — there is no complex scoring system to "confirm" it. The diagnosis is made at the bedside the moment two criteria are met simultaneously.

Neutropenic fever is diagnosed when BOTH of the following are present ^[1]^[2]^[3]^[4]^[5]^[6]:

Neutropenia: ANC ≤ 0.5 × 10⁹/L (≤ 500/µL), OR ANC ≤ 1.0 × 10⁹/L with a predicted decline to ≤ 0.5 × 10⁹/L within 24–48 hours

Fever: Single oral temperature ≥ 38.3°C, OR persistent temperature ≥ 38.0°C sustained over ≥ 1 hour

Term	Definition	Clinical Significance
Neutropenia	ANC ≤ 1.5 × 10⁹/L	Mild; low infection risk
Severe neutropenia	ANC ≤ 0.5 × 10⁹/L	Threshold for neutropenic fever diagnosis; infection risk rises sharply
Profound neutropenia	ANC ≤ 0.1 × 10⁹/L	Very high risk; highest mortality; qualifies as high-risk category

ANC Calculation (from first principles):

\text{ANC} = \text{Total WBC} \times \frac{(\% \text{Neutrophils} + \% \text{Bands})}{100}

Why include bands? Band cells (immature neutrophils with unsegmented nuclei) represent the most mature marrow reserve that has been mobilised. Including them gives a better reflection of the total functional neutrophil pool. In severe neutropenia, even bands will be depleted.

Common Exam Pitfall

The diagnosis of neutropenic fever does NOT require a positive blood culture or identification of a source. Pathogens can only be identified in 20–30% of cases ^[1]^[5]. The diagnosis is purely clinical — ANC + temperature. Do not delay treatment waiting for culture results.

Once the diagnosis of neutropenic fever is made, the next step is risk stratification, which determines the intensity of management:

MASCC (Multinational Association for Supportive Care in Cancer) Risk Index ^[5]:

Characteristic	Score
Burden of illness: no or mild symptoms	5
Burden of illness: moderate symptoms	3
No hypotension (SBP ≥ 90 mmHg)	5
No COPD	4
Solid tumour or no previous fungal infection in haematological malignancy	4
No dehydration requiring IV fluids	3
Outpatient at onset of fever	3
Age < 60 years	2
Maximum	26

MASCC score ≥ 21 → Low risk (PPV ~91%; mortality ~3%) MASCC score < 21 → High risk (mortality ~36%)

High-risk criteria (any one = high risk, requires inpatient IV antibiotics) ^[5]:

Anticipated prolonged (≥ 7 days) or profound (ANC < 0.1 × 10⁹/L) neutropenia
Medical co-morbidities: haemodynamically unstable, deranged LRFT, altered mental state
MASCC score < 21

Low-risk criteria ^[5]:

Expected short duration of neutropenia (≤ 7 days)
No significant comorbidities
MASCC score ≥ 21
In Hong Kong, outpatient management of low-risk patients is seldom practised ^[5] — most patients are admitted

The algorithm below integrates the GC lecture slide approach ^[9] and IDSA guidelines. The key principle is: blood cultures first → empirical antibiotics IMMEDIATELY (within 1 hour) → then systematic investigation and risk stratification in parallel.

"Full Hx & P/E (daily): skin, oral, lung, abdomen, perianal, Hickman exit, BM Bx site; over nasal sinus" ^[9]

GC High Yield — Order of Operations

The approach to management of neutropenic fever ^[9]:

Full Hx & P/E (daily)
Ix: general (CBP, LFT, RFT); blood cultures from central venous catheter through two different ports (peripheral venous puncture if infected catheter suspected)
Start empirical broad-spectrum antibiotics
CXR: low risk; CT lung: high risk or symptomatic
Abdomen CT scan: abdominal pain, tenderness, diarrhea
Stool × Clostridium difficile cytotoxin & culture: Diarrhea+
Urine, skin swab, sputum, bronchoalveolar lavage (BAL) for testing (serial serum galactomannan / 1,3 beta-D-glucan): usually done if symptoms or clinical/radiological lesions+ ^[9]

III. Investigation Modalities

Investigations serve three purposes simultaneously:

Identify the causative organism (cultures, serology, molecular tests)
Identify the source/site of infection (imaging, directed cultures)
Assess severity and organ function (bloods, lactate, ABG)

A. Blood Investigations

Parameter	Expected Finding	Interpretation / Why
ANC	≤ 0.5 × 10⁹/L	Confirms the diagnosis; guides severity grading
Haemoglobin	Often ↓	Marrow suppression → anaemia; concurrent bleeding (thrombocytopaenia)
Platelets	Often ↓	Marrow suppression → thrombocytopaenia → bleeding risk; may need platelet transfusion
Peripheral blood smear	May show left shift, blasts, or no abnormal cells	Left shift (band cells, metamyelocytes) suggests severe infection/sepsis ^[12]; blasts suggest relapsed leukaemia; absence of neutrophils in the context of pancytopaenia

Why check the differential? Not all neutropaenia is the same. A patient with ANC 0.3 who has some monocytes retained has slightly better innate defence than one with ANC 0.0 and no monocytes at all. The differential also helps detect concurrent lymphopaenia (risk of PJP, viral reactivation) or eosinophilia (drug reaction, parasitic infection).

Ix: general (CBP, LFT, RFT) ^[9]^[5]

Test	Expected Finding	Interpretation
Creatinine / eGFR	May be ↑	Sepsis-induced AKI (pre-renal → intrinsic); dehydration; nephrotoxic drugs (aminoglycosides, amphotericin B)
Urea	May be disproportionately ↑ compared to Cr	Pre-renal AKI (dehydration, sepsis); also raised in GI bleeding (e.g. from thrombocytopaenic mucosal bleeding)
ALT / AST	May be ↑	"Shock liver" from hypoperfusion; hepatic candidiasis; drug hepatotoxicity
ALP / GGT	May be ↑	Biliary obstruction (cholangitis); hepatic infiltration (hepatosplenic candidiasis)
Bilirubin	May be ↑	Sepsis; hepatic dysfunction; haemolysis (if transfusion reaction)
Albumin	Often ↓	Negative acute-phase reactant; chronic illness; capillary leak in sepsis

Bloods: CBC d/c, LRFT, CaPO₄ lactate ^[5]

Test	Key Findings	Why
Na⁺	May be ↓	SIADH from infection/drugs; or dilutional from IV fluid resuscitation
K⁺	May be ↑ or ↓	↑K⁺ in AKI, tumour lysis syndrome (TLS); ↓K⁺ from GI losses (diarrhoea, vomiting)
Ca²⁺ / PO₄	Abnormal in TLS	Look for evidence of tumour lysis syndrome: hyperK, hyperPO₄, hypoCa, ↑uric acid, ↑LDH ^[4]
Lactate	↑ in sepsis	Lactate > 2 mmol/L indicates tissue hypoperfusion; lactate > 4 mmol/L suggests septic shock and mandates aggressive resuscitation; serial lactate is used to guide response to treatment

Why is lactate so important? In sepsis, vasodilation + capillary leak → inadequate oxygen delivery to tissues → cells switch to anaerobic glycolysis → pyruvate is converted to lactate. Rising lactate = worsening tissue hypoxia = failing resuscitation. It is the single best prognostic marker in sepsis.

Marker	Utility	Interpretation
CRP	↑ in infection and inflammation	Non-specific; rises within 6–8 hours; useful for trending response to treatment; note that CRP can be elevated by tumour, surgery, and drugs
Procalcitonin (PCT)	More specific for bacterial infection	PCT < 0.5 ng/mL makes bacterial infection less likely; PCT > 2 ng/mL strongly suggests bacterial sepsis. Useful for antibiotic stewardship (de-escalation when PCT trending down). PCT is NOT elevated by viral infections or steroids
ESR	↑ in infection and inflammation	Very non-specific; slow to rise and fall; limited utility in acute setting
Serum ferritin	Markedly ↑ in HLH/MAS	Ferritin > 10,000 µg/L highly suggestive of HLH (haemophagocytic lymphohistiocytosis)

Test	Finding	Significance
PT / INR, APTT, Fibrinogen	Prolonged PT/APTT, ↓fibrinogen, ↑D-dimer	DIC (disseminated intravascular coagulation) — triggered by Gram-negative sepsis, APML, or severe sepsis of any cause; check clotting to guide blood product support

Finding	Interpretation
Metabolic acidosis (↓pH, ↓HCO₃⁻, ↑lactate)	Lactic acidosis from septic shock — tissue hypoperfusion
Respiratory alkalosis (↓pCO₂)	Early sepsis — tachypnoea driven by cytokines
Hypoxia (↓pO₂)	Pneumonia, ARDS, pulmonary oedema from fluid overload

B. Microbiological Investigations (The Centrepiece)

Blood cultures from central venous catheter through two different ports (peripheral venous puncture if infected catheter suspected) ^[9]

Aspect	Detail	Rationale
Timing	Immediately, before starting antibiotics ^[5]^[13]	Once antibiotics are given, cultures may be sterilised and the opportunity to identify the organism is lost
Number	At least 2 sets (1 set = 1 aerobic + 1 anaerobic bottle)	Multiple sets increase sensitivity (single set: ~65%; 2 sets: ~80%; 3 sets: ~96%) and help distinguish true bacteraemia from contamination
Sites	From CVC through two different lumens/ports + peripheral venous puncture ^[3]^[4]^[9]	Differential time to positivity (DTTP): if CVC culture turns positive ≥ 2 hours before the peripheral culture, it suggests catheter-related bloodstream infection (CRBSI); peripheral site also avoids false positives from catheter biofilm contamination
Volume	Adults: 20–30 mL per set (10 mL per bottle)	Volume is the single most important factor for culture yield — underfilling bottles is the most common error

Differential Time to Positivity (DTTP)

If the blood culture drawn from the CVC becomes positive ≥ 2 hours earlier than the peripheral blood culture drawn simultaneously, this strongly suggests the catheter is the source of infection (CRBSI). This is because the bacterial load is higher at the catheter biofilm, so the culture detects growth sooner. This distinction matters because CRBSI may require catheter removal.

"Urine, Skin swab, sputum, Bronchoalveolar lavage (BAL) for testing... usually done if symptoms or clinical/radiological lesions+" ^[9]

Specimen	When to Collect	Key Points
Urine culture	All patients (routine); especially with urinary symptoms or indwelling catheter	Note: pyuria may be absent in neutropenic patients (no neutrophils to produce WBCs in urine) — a negative dipstick does NOT exclude UTI
Sputum culture (including AFB smear)	Productive cough; respiratory symptoms	May be difficult to produce adequate sample in mucositis; if unable, consider induced sputum or BAL
Stool	Diarrhoea+ ^[9]	Stool for C. difficile cytotoxin and culture ^[9]^[3]^[4]; also consider stool culture for other enteric pathogens, ova and parasites
Skin / wound swab	Cellulitis, catheter exit site erythema, skin lesions	Culture for bacteria + fungi; consider biopsy for persistent or atypical lesions (e.g. ecthyma gangrenosum)
CSF (lumbar puncture)	Meningism, altered consciousness, focal neurology	Only if safe (no raised ICP on CT brain first; platelet count adequate → correct to > 50 × 10⁹/L before LP); send for cell count, protein, glucose, Gram stain, culture, viral PCR, cryptococcal antigen if relevant
Bronchoalveolar lavage (BAL)	Persistent pulmonary infiltrates unresponsive to empirical antibiotics; suspicion of PJP, Aspergillus, or atypical pneumonia	Send for bacterial culture, fungal culture, AFB, galactomannan, PJP stain/PCR, viral PCR (respiratory panel); usually done if symptoms or clinical/radiological lesions+ ^[9]

Test	Target Pathogen	Interpretation	When to Order
Serum galactomannan (GM)	Aspergillus	GM is a cell wall component of Aspergillus released during fungal growth; serial monitoring ^[9]; GM index > 0.5 (single) or > 0.7 (BAL) is positive; Sensitivity ~70%, Specificity ~90% in haem-onc patients	Persistent fever > 4–7 days despite antibiotics; high-risk patients (prolonged neutropenia, HSCT)
1,3 β-D-glucan (BDG)	Pan-fungal (Candida, Aspergillus, PJP — but NOT Mucorales or Cryptococcus)	BDG is a cell wall component of most fungi; > 80 pg/mL is positive; Sensitivity 77%, Specificity 85%	Same as above; complements galactomannan; particularly useful for PJP (Sens ~95%)
CMV PCR (viral load)	CMV reactivation	Quantitative PCR; detectable viral load indicates reactivation; rising titres warrant pre-emptive treatment	Post-HSCT, post-organ transplant, prolonged lymphopaenia
EBV PCR (viral load)	EBV reactivation / PTLD	Rising EBV viral load suggests risk of post-transplant lymphoproliferative disorder	Post-HSCT, post-organ transplant
HSV / VZV PCR	HSV, VZV	PCR of vesicle swab or blood; confirms herpetic infection	Vesicular skin lesions, atypical oral ulcers
Respiratory virus multiplex PCR	Influenza, RSV, adenovirus, parainfluenza, SARS-CoV-2	Nasopharyngeal aspirate (NPA) or swab; rapid results	Upper/lower respiratory symptoms, coryza
HIV serology	HIV	Should be checked if not previously done; HIV causes severe immunosuppression and changes the differential (PJP, TB, Cryptococcus, Talaromyces)	New diagnosis of severe infection in young patient; unexplained lymphopaenia
Cryptococcal antigen (CrAg)	Cryptococcus neoformans	Serum and/or CSF CrAg; highly sensitive and specific	Suspected meningitis in immunocompromised; headache + fever

Galactomannan vs β-D-Glucan — Know the Difference

	Galactomannan	1,3 β-D-Glucan
Specificity	Aspergillus-specific	Pan-fungal (most fungi except Mucor and Crypto)
Source	Aspergillus cell wall	Cell wall of most fungi
False positives	Piperacillin-tazocin (Tazocin), amoxicillin-clavulanate	Haemodialysis membranes, albumin infusions, some antibiotics
Role	Serial monitoring for invasive aspergillosis	Screening for any invasive fungal infection

Exam pearl: Galactomannan can be falsely positive in patients receiving piperacillin-tazocin (Tazocin) — which is the most commonly used first-line empirical antibiotic in neutropenic fever. Be aware of this when interpreting results.

C. Imaging Investigations

CXR: low risk; CT lung: high risk or symptomatic ^[9]

Finding	Interpretation	Caveat
Consolidation / infiltrate	Pneumonia (bacterial, fungal, viral)	Consolidation may be absent due to inability to mount inflammatory response ^[5] — a normal CXR does NOT rule out pneumonia in a neutropenic patient
Bilateral diffuse ground-glass	PJP, viral pneumonia, pulmonary oedema, ARDS	Clinical correlation required
Pleural effusion	Parapneumonic effusion, empyema, or non-infectious (malignant)	May warrant diagnostic thoracocentesis
Multiple cavitating lesions	Septic emboli (from endocarditis or line sepsis), Aspergillus, Nocardia, TB	Consider echocardiogram to rule out endocarditis
Normal CXR	Does NOT exclude pulmonary infection	Low sensitivity in neutropenic patients; proceed to CT if clinical suspicion is high

CT lung: high risk or symptomatic ^[9]

Finding	Pathogen Suggested	Why
"Halo sign" (ground-glass halo surrounding a nodule)	Invasive pulmonary aspergillosis (IPA) — early sign	The halo represents haemorrhage around the fungal nodule due to angioinvasion by Aspergillus hyphae; best seen early (Day 0–5 of disease)
"Air-crescent sign" (crescent of air within a nodule)	IPA — late sign	Occurs as neutrophils recover and necrotic fungal tissue separates from viable lung → cavity forms; typically seen Day 10–20
"Reversed halo sign" (ring of consolidation around central ground-glass)	Mucormycosis, organising pneumonia	Less specific than halo sign
Diffuse bilateral ground-glass opacities	PJP, CMV pneumonitis, viral pneumonia	Correlate with β-D-glucan, CMV PCR, respiratory viral panel
Tree-in-bud pattern, centrilobular nodules	TB, atypical mycobacteria, viral bronchiolitis	Send sputum for AFB
Wedge-shaped peripheral infarcts	Septic emboli (from CRBSI), pulmonary embolism	Consider echocardiogram; CT pulmonary angiography if PE suspected

Abdomen CT scan: abdominal pain, tenderness, diarrhea ^[9]

Finding	Diagnosis	Key Features
Caecal wall thickening (> 4 mm), pericolonic fat stranding ± pneumatosis	Neutropenic enterocolitis (typhlitis)	Involvement of caecum/ascending colon; may show intramural air (pneumatosis) suggesting necrosis → perforation risk
Colonic wall thickening, "accordion sign"	C. difficile colitis	Pancolitis or segmental; "accordion sign" = alternating bands of contrast-enhancing mucosa and low-density oedema
Hepatosplenic micro-abscesses ("bull's-eye" lesions)	Hepatosplenic candidiasis (chronic disseminated candidiasis)	Multiple small low-density lesions in liver and spleen; classically becomes visible as neutrophils recover → "unmasking"
Peri-appendiceal inflammation	Appendicitis (may lack typical signs in neutropenia)	CT helps differentiate from typhlitis

Finding	Diagnosis	Why
Mucosal thickening, air-fluid levels, bony erosion	Fungal sinusitis (Aspergillus, Mucor)	Prolonged neutropenia + sinus symptoms; bony erosion suggests invasive fungal disease; may require urgent surgical debridement for Mucor

Indication	Finding	Interpretation
Persistent bacteraemia (especially S. aureus > 48 h despite antibiotics); new murmur; embolic phenomena	Vegetation on valve, abscess, new valvular regurgitation	Infective endocarditis — diagnosed by Modified Duke Criteria ^[14]; TTE as initial screen; TEE if TTE negative but suspicion high

D. Special Investigations for Specific Scenarios

Indication	What to Send	Key Findings
Suspected meningitis/encephalitis (headache, neck stiffness, altered consciousness, focal neurology)	Cell count, protein, glucose, Gram stain, bacterial culture, viral PCR (HSV, VZV, enterovirus), fungal culture, CrAg, AFB	Must do CT brain first if any concern for raised ICP (altered consciousness, focal signs, papilloedema, seizure) ^[15]; correct platelets to > 50 × 10⁹/L and INR < 1.5 before LP
CSF findings in neutropenic patient	May show ↓WCC (neutropenic → fewer cells in CSF) but still have ↑protein and ↓glucose	Paucity of CSF pleocytosis does NOT exclude meningitis — interpret with caution

Indication	Purpose
If uncertain whether neutropenia is due to chemotherapy vs. disease relapse; prolonged unexplained cytopenias; suspected marrow infiltration (fungal, mycobacterial)	Assess cellularity, residual disease, marrow fibrosis; culture marrow for fungi/AFB; flow cytometry for relapsed leukaemia

Indication	Purpose
Atypical skin lesions not responding to empirical therapy; pulmonary nodules on CT; hepatosplenic lesions	Histology (fungal hyphae, granulomata for TB); tissue culture; molecular studies (PCR)

Category	Investigations	Key Findings
Bloods — Routine	CBP d/c, LRFT, CaPO₄, lactate ^[5]^[9]	ANC for diagnosis; LRFT for organ dysfunction; lactate for sepsis severity; CaPO₄ for TLS
Bloods — Inflammatory	CRP, procalcitonin	Trending CRP; PCT for bacterial vs non-bacterial
Bloods — Coagulation	PT/INR, APTT, fibrinogen, D-dimer	DIC screen
Bloods — ABG	ABG + lactate	Metabolic acidosis, hypoxia, lactate
Cultures — Blood	≥ 2 sets: from CVC (two ports) + peripheral ^[9]	Organism identification, DTTP for CRBSI
Cultures — Directed	Urine, sputum, stool (C. diff), skin swab, CSF, BAL ^[9]	Site-specific organism identification
Fungal markers	Serial serum galactomannan, 1,3 β-D-glucan ^[9]	Invasive aspergillosis, pan-fungal screening
Viral markers	CMV/EBV PCR, respiratory viral panel, HSV/VZV PCR	Viral reactivation, respiratory viruses
Imaging — CXR	Low risk patients; first-line ^[9]	Pneumonia (may be normal despite infection)
Imaging — CT thorax	High risk or symptomatic ^[9]	Halo sign (Aspergillus), GGO (PJP, viral), emboli
Imaging — CT abdomen	Abdominal pain, tenderness, diarrhoea ^[9]	Typhlitis, C. diff colitis, hepatosplenic candidiasis
Imaging — CT sinus	Sinus symptoms, prolonged neutropenia	Fungal sinusitis
Special	Echocardiography, LP, BM biopsy, tissue biopsy	As clinically indicated

The following flowchart summarises the complete diagnostic pathway from presentation to organism identification:

GC Exam — Key Investigation Steps

From GC 102 lecture slides ^[9], the investigation approach can be summarised as:

General bloods: CBP, LFT, RFT
Blood cultures from CVC through two different ports; peripheral venous puncture if infected catheter suspected
CXR: low risk; CT lung: high risk or symptomatic
CT abdomen: if abdominal pain, tenderness, diarrhea
Stool × C. difficile cytotoxin & culture: if Diarrhea+
Urine, Skin swab, sputum, BAL for testing
Serial serum galactomannan / 1,3 beta-D-glucan: usually done if symptoms or clinical/radiological lesions+

This is the framework to remember for the written paper.

High Yield Summary — Diagnosis and Investigations

Diagnostic Criteria:

ANC ≤ 0.5 (or ≤ 1.0 with predicted decline to ≤ 0.5 in 48h) + Temp ≥ 38.3°C single or ≥ 38.0°C for ≥ 1h
Clinical diagnosis — does NOT require positive culture

Risk Stratification:

MASCC score ≥ 21 = low risk; < 21 = high risk
High risk if: prolonged neutropenia ≥ 7 days, profound ANC < 0.1, haemodynamic instability, organ dysfunction

Key Investigations:

Blood cultures FIRST (CVC two ports + peripheral) → then antibiotics within 1 hour
Baseline: CBP d/c, LRFT, CaPO₄, lactate, coag, ABG
CXR for all; CT thorax for high risk or symptomatic (look for halo sign)
CT abdomen for abdominal symptoms (typhlitis, C. diff colitis)
Stool C. difficile toxin/PCR if diarrhoea
Serial galactomannan + β-D-glucan if persistent fever > 4–7 days
Directed cultures: urine, sputum, skin swab, BAL, CSF as clinically indicated

Pitfalls:

Normal CXR does NOT exclude pneumonia (no neutrophils to form infiltrate)
Absent pyuria does NOT exclude UTI
Paucity of CSF pleocytosis does NOT exclude meningitis
Galactomannan falsely positive with piperacillin-tazocin

Active Recall - Diagnostic Criteria, Algorithm and Investigations for Neutropenic Fever

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 423, Complications of Leukemia — Neutropenic Fever) ^[2] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p. 11, Haematological Emergencies) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 1329–1333, Neutropenic fever) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 572–574, 745, Neutropenic fever) ^[5] Senior notes: Maksim Medicine Notes.pdf (p. 49, Clinical oncology — Neutropenic fever) ^[6] Senior notes: Ryan Ho Haemtology.pdf (p. 70, Complications of Leukaemia — Neutropenic Fever) ^[9] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf (p. 8, Approach to Mx of neutropenic fever) ^[12] Senior notes: Ryan Ho Fundamentals.pdf (p. 390–391, Clinical evaluation and Workup) ^[13] Senior notes: Learning_Points_All_Lectures.txt (Learning Point 3 — febrile neutropenia as medical emergency requiring blood cultures and antibiotics within one hour) ^[14] Senior notes: Block A - Fever and a murmur_ Valvular heart diseases; Infective endocarditis.pdf (p. 32–33, Modified Duke Criteria) ^[15] Senior notes: Ryan Ho Neurology.pdf (p. 145, Approach to meningitis investigations)

Management of Neutropenic Fever

Neutropenic fever is a medical emergency because unchecked proliferation of bacteria can lead to rapid progression into septic shock, especially in Gram-negative sepsis ^[1]. Empirical antibiotics must be started ASAP after immediate septic workup — ideally < 1–2 hours after presentation ^[1]^[13].

The management philosophy can be broken down into five pillars:

Immediate resuscitation and stabilisation
Empirical antibiotics (the cornerstone — given before culture results)
Adjustment based on clinical course and culture results (escalation or de-escalation)
Addition of antifungal agents if fever persists
Supportive measures (G-CSF, transfusion support, infection prevention)

Before anything else, assess the patient for sepsis and septic shock. This determines the urgency of everything that follows.

Action	Detail	Rationale
ABCDE approach	Airway, Breathing, Circulation, Disability, Exposure	Standard emergency assessment; a neutropenic patient in septic shock needs the same resuscitation as any other septic patient
IV access	Establish peripheral IV (even if CVC present)	Peripheral access ensures drug delivery if CVC is the source of infection and needs removal
Fluid resuscitation	IV crystalloid (0.9% NaCl or Ringer's Lactate) 30 mL/kg bolus over 1–3 hours if haemodynamically unstable	Septic shock causes vasodilation and capillary leak → intravascular volume depletion → organs underperfused; fluids restore circulating volume
Vasopressors	Noradrenaline first-line if MAP < 65 mmHg despite adequate fluid resuscitation	Noradrenaline causes vasoconstriction (α₁ agonist) → restores SVR and MAP → maintains organ perfusion
Oxygen	Supplemental O₂ to maintain SpO₂ > 94%	Tissue hypoxia worsens lactic acidosis
Monitoring	Continuous cardiac monitoring, hourly BP/Pulse/UO, serial lactate	Lactate clearance > 20% in first 6 hours indicates adequate resuscitation

III. Empirical Antibiotic Therapy — The Cornerstone

The principle of empirical therapy is timely ( < 1–2 hours) administration of broad-spectrum antibiotics that cover most pathogens, especially P. aeruginosa ^[1]

Why anti-pseudomonal cover is mandatory: Pseudomonas aeruginosa produces endotoxin (LPS) that triggers a fulminant inflammatory cascade → septic shock within hours. Without empirical cover, mortality from Pseudomonas bacteraemia in neutropenic patients exceeds 30–40%. Every hour of delay in appropriate antibiotics increases mortality by approximately 7%.

B. Choice of Empirical Regimen — By Risk Category

Empirical IV broad-spectrum anti-pseudomonal antibiotics for a course of at least 7 days ^[5]

The standard approach is anti-pseudomonal monotherapy. The following agents are first-line options:

Drug	Dose	Mechanism	Why This Drug
IV Piperacillin-tazobactam (Tazocin) 4.5g Q6–8h ^[5]^[6]^[3]	4.5g Q6–8h IVI	Beta-lactam + beta-lactamase inhibitor; inhibits bacterial cell wall synthesis; tazobactam extends spectrum to cover many beta-lactamase producers	Covers Gram-negatives (including Pseudomonas), many Gram-positives, and anaerobes; most commonly used first-line in HK
Ceftazidime (Fortum) 1–2g Q8h IV ^[5]^[6]	1–2g Q8h IV	3rd-generation cephalosporin with excellent anti-pseudomonal activity	Good Gram-negative cover but poor Gram-positive cover; no anaerobic cover
Cefepime 2g Q8–12h IV ^[5]^[6]^[3]	2g Q8–12h IVI	4th-generation cephalosporin; broader Gram-positive cover than ceftazidime while maintaining anti-pseudomonal activity	Better balance of Gram-positive and Gram-negative cover
Meropenem 1g Q8h IVI ^[5]^[6]^[3]	1g Q8h IVI	Carbapenem; broadest spectrum beta-lactam; inhibits cell wall synthesis; resistant to most beta-lactamases including ESBLs and AmpC	Reserved for patients at high risk of resistant organisms (ESBL producers, prior colonisation); avoid as first-line to prevent carbapenem resistance
Imipenem-cilastatin 500mg Q6h IVI ^[5]^[6]^[3]	500mg Q6h IVI	Carbapenem (same class as meropenem); cilastatin prevents renal metabolism of imipenem	Alternative carbapenem; lowers seizure threshold more than meropenem (avoid in CNS infections or seizure history)

GC High Yield — First-Line Antibiotic Choice

From GC 102 ^[9]: The emphasis is on starting empirical broad-spectrum antibiotics after cultures. In Hong Kong practice, Tazocin (piperacillin-tazobactam) is the most commonly used first-line agent. Carbapenems (meropenem) are reserved for patients with risk factors for resistant organisms or documented ESBL-producing infections.

ADD additional antibiotics for selected cases ^[6]^[3]^[4]:

Indication	Agent to Add	Dose	Rationale
Haemodynamic instability / septic shock	Aminoglycoside: IV Gentamicin or Amikacin ^[5]^[6]	Gentamicin 5 mg/kg Q24h or Amikacin 15 mg/kg Q24h	Synergistic bactericidal activity with beta-lactams against Gram-negatives; rapid killing of Pseudomonas; double Gram-negative cover for critically ill patients
Suspected MRSA, catheter-related infection, skin/soft tissue infection, pneumonia, or haemodynamic instability	Vancomycin ^[3]^[4]^[6]	500mg Q6h or 1g Q12h IV (adjust for renal function; target trough 15–20 µg/mL)	Covers MRSA, CoNS (if resistant to beta-lactams), viridans streptococci with reduced penicillin susceptibility
Suspected intra-abdominal / perianal infection	Metronidazole	500mg Q8h IV	Covers anaerobes (Bacteroides, Clostridium spp.) which are not well covered by ceftazidime or cefepime
C. difficile colitis	Oral Vancomycin	125–250mg Q6h PO (NOT IV — oral vancomycin stays in the gut lumen)	IV vancomycin does not reach therapeutic levels in the colonic lumen; oral vancomycin achieves high intraluminal concentrations

Why not give Vancomycin routinely to everyone? Routine vancomycin adds nephrotoxicity (especially combined with aminoglycosides), promotes VRE (vancomycin-resistant enterococci), and has not been shown to improve outcomes in unselected patients. It should only be added when there is a specific clinical indication ^[3]^[4].

Aminoglycoside Safety

Aminoglycosides (gentamicin, amikacin) are nephrotoxic and ototoxic. Monitor renal function and drug levels closely. Extended-interval dosing (once daily) maximises bactericidal activity (concentration-dependent killing) while minimising toxicity. Avoid combining with other nephrotoxins (amphotericin B, vancomycin) when possible — but in life-threatening septic shock, the benefit outweighs the risk.

Low risk (outpatient) — seldom in HK ^[5]

Oral Regimen	Dose	Note
Amoxicillin-clavulanate + Ciprofloxacin ^[3]^[4]	Amoxicillin-clavulanate 625mg Q8h PO + Ciprofloxacin 500mg Q12h PO	Only for MASCC ≥ 21, expected neutropenia ≤ 7 days, no comorbidities, reliable patient with caregiver access
Levofloxacin monotherapy	750mg Q24h PO	Alternative if already on fluoroquinolone prophylaxis — NOT appropriate (use IV regimen instead)

If fluoroquinolone has been used for prophylaxis, use regimen as for high risk ^[6]. Why? Because the organisms in a patient already on fluoroquinolone prophylaxis have been selected for fluoroquinolone resistance, making oral fluoroquinolone-based therapy unreliable.

Contraindications to outpatient oral therapy:

MASCC < 21
Anticipated neutropenia ≥ 7 days or ANC < 0.1
Haemodynamic instability
Organ dysfunction (deranged LRFT)
Altered mental state
GI symptoms that may impair oral absorption (vomiting, mucositis, diarrhoea)
Already on fluoroquinolone prophylaxis
No reliable caregiver or access to emergency care within 1 hour

This is the critical decision point. By 48–72 hours, preliminary culture results may be available and the clinical trajectory becomes clearer.

Key Decisions at 48–72 Hours

Scenario	Action	Rationale
Culture positive, susceptible organism	De-escalate to narrowest effective antibiotic	Antibiotic stewardship — reduces side effects, prevents resistance, reduces cost
Culture positive, resistant organism	Escalate to appropriate agent (e.g. carbapenem for ESBL-producer; vancomycin for MRSA)	Resistance means the current antibiotic is not killing the organism
Culture negative, clinically improving	Continue current regimen; consider de-escalation if afebrile ≥ 48h and ANC recovering	Most neutropenic fever episodes are culture-negative; clinical improvement is the best indicator
Culture negative, persistent fever	Repeat cultures; review imaging; check galactomannan/β-D-glucan; consider broadening coverage	Persistent fever suggests inadequate coverage, fungal infection, line sepsis, or non-infectious cause
Clinical deterioration	Broaden antibiotics (add aminoglycoside + vancomycin if not already); ICU review; urgent imaging	Impending septic shock; need maximal antimicrobial coverage + haemodynamic support

V. Antifungal Therapy

Antifungal agents should be initiated for neutropenic fever after 4–7 days (~5 days) of persistent fever despite broad-spectrum antibacterials ^[3]^[4]^[6]

Why 4–7 days? By this point, most bacterial infections should have responded to empirical antibiotics. Persistent fever in the face of adequate antibacterial coverage raises the probability of invasive fungal infection (IFI) — particularly in patients with prolonged neutropenia ( > 7 days) or haematological malignancy.

Agent	Dose	Spectrum	Advantages	Disadvantages
Caspofungin	70mg IV Day 1, then 50mg Q24h	Candida spp., Aspergillus spp. (fungicidal for Candida, fungistatic for Aspergillus)	Well tolerated; few drug interactions; effective against most Candida including azole-resistant strains	No activity against Mucor, Cryptococcus; only IV formulation
Liposomal Amphotericin B (L-AmB)	3–5 mg/kg/day IV	Broadest spectrum: Candida, Aspergillus, Mucor, Cryptococcus	Covers Mucor (unlike echinocandins and voriconazole); liposomal formulation much less nephrotoxic than conventional amphotericin B	Nephrotoxicity (less than conventional but still significant); infusion-related reactions (fever, rigors); hypokalaemia; expensive
Voriconazole	6 mg/kg Q12h IV Day 1, then 4 mg/kg Q12h IV (or 200mg Q12h PO)	Aspergillus (drug of choice), Candida, Fusarium; NO activity against Mucor	Excellent tissue penetration including CNS; oral formulation available for step-down	Visual disturbances (transient, reversible); hepatotoxicity; photosensitivity; many CYP450 drug interactions; no Mucor cover
Posaconazole	300mg Q12h Day 1, then 300mg Q24h (IV or PO delayed-release tablet)	Aspergillus, Candida, Mucor	Covers Mucor (unlike voriconazole); excellent prophylaxis agent	Needs therapeutic drug monitoring; absorption of oral suspension variable (delayed-release tablet preferred)

Empirical vs. Pre-emptive vs. Targeted Antifungal Strategy

Strategy	Trigger	Typical Agents
Empirical	Persistent fever > 4–7 days despite Abx, no organism identified	Caspofungin, L-AmB
Pre-emptive	Positive galactomannan, β-D-glucan, or CT changes (halo sign) but no definitive diagnosis	Voriconazole (for likely Aspergillus), L-AmB
Targeted	Confirmed IFI by culture or histology	Agent based on organism identification and susceptibility

The pre-emptive approach is increasingly favoured in guidelines because it avoids unnecessary antifungal exposure in patients whose persistent fever is due to non-fungal causes, while still treating those with objective evidence of IFI.

Organism	Drug of Choice	Alternative	Duration
Candida spp.	Echinocandin (caspofungin, micafungin, anidulafungin) for candidaemia	Fluconazole if susceptible (step-down after initial echinocandin)	≥ 14 days after last positive blood culture + resolution of signs
Aspergillus spp.	Voriconazole (primary)	L-AmB, posaconazole, isavuconazole	≥ 6–12 weeks; guided by clinical and radiological response + immune recovery
Mucormycosis	L-AmB (high dose: 5–10 mg/kg/day) + surgical debridement	Posaconazole, isavuconazole (step-down after stabilisation)	Prolonged; surgical debridement is essential; antifungal alone is insufficient
PJP (Pneumocystis)	Co-trimoxazole (TMP-SMX) 15–20 mg/kg/day TMP component, divided Q6–8h, for 21 days	Pentamidine IV; clindamycin + primaquine; atovaquone	21 days; add prednisolone if PaO₂ < 70 mmHg (reduces mortality in moderate-severe PJP)

MUST check G6PD status before starting co-trimoxazole — sulphamethoxazole (SMX) is a sulphonamide and can cause haemolysis in G6PD-deficient patients. This is particularly important in HK where G6PD deficiency prevalence is approximately 4–5% in males.

The duration depends on whether a source/organism was identified and on neutrophil recovery:

Scenario	Duration	Rationale
Known source identified	Complete standard course for that infection (usually 14 days) ^[3]^[4]	Treat the infection as you would in any patient, but ensure the full course is completed because the immune system cannot mop up residual organisms
Unknown source (FUO), afebrile and ANC recovering	Continue antibiotics until afebrile ≥ 48 hours AND ANC > 0.5 × 10⁹/L ^[3]^[4]	The neutrophils are the patient's best defence; once they recover, the risk of relapse drops dramatically
Unknown source, afebrile but ANC NOT recovering	Continue antibiotics until Day 14 or until ANC > 0.5, whichever comes first; then reassess	Prolonged antibiotics in persistent neutropenia carry risk of C. difficile, fungal superinfection, and resistance; clinical judgement required
Persistent fever, no source identified, ANC recovering	Continue antibiotics for 4–5 days after ANC > 0.5; reassess for non-infectious causes	Neutrophil recovery may unmask previously subclinical infections (e.g. hepatosplenic candidiasis)

Empirical IV broad-spectrum anti-pseudomonal antibiotics for a course of at least 7 days ^[5]

VII. Supportive Measures

G-CSF (granulocyte colony-stimulating factor) and GM-CSF (granulocyte-macrophage CSF) are NOT recommended for routine use in patients with neutropenic fever ^[3]^[4]

Aspect	Detail
Mechanism	G-CSF (filgrastim, pegfilgrastim) stimulates myeloid progenitor proliferation and differentiation → accelerates neutrophil recovery
Indication (therapeutic)	Can be "considered" as adjuvant therapy in high-risk patients ^[3]^[4] — specifically: septic shock, fungal infection, or severe pneumonia ^[1]^[6]
When to stop	Stop G-CSF when neutrophil count returns to 1.0 × 10⁹/L ^[1]^[6]
Why NOT routine?	G-CSF may increase inflammatory response (theoretically worsening ARDS or capillary leak); no consistent survival benefit in randomised trials; cost; fever from G-CSF itself complicates assessment
Contraindication	Do NOT give G-CSF concurrently with chemotherapy (can sensitise rapidly dividing myeloid progenitors to the cytotoxic agent → paradoxically worsen myelosuppression)

Buffy coat (WBC) transfusion: must be irradiated to prevent lymphocyte proliferation (associated with TA-GVHD) ^[1]^[6]^[16]

Aspect	Detail
Indication	Neutropenic fever (ANC < 0.5) PLUS documented infection not responding to broad-spectrum antibiotics + antifungal for ≥ 48 hours ^[1]^[6]
Dose	10 units/day for ≥ 4 days and until fever subsides ^[1]^[6]
Why irradiate?	Irradiation targets lymphocytes in the blood product → prevents lymphocyte proliferation → prevents transfusion-associated graft-versus-host disease (TA-GVHD) ^[16]; TA-GVHD is almost universally fatal in immunocompromised patients
Storage	Room temperature (20–24°C); shelf life only 8 hours ^[16] — must be used almost immediately after collection
Practical limitation	Rarely requested by physicians other than haematologists ^[16]; logistically challenging due to extremely short shelf life

Emergency — No Irradiated Blood Available

If an immunocompromised patient urgently requires blood products and irradiated products are unavailable: Ask the blood bank for the oldest bag of blood — once blood is stored for > 14 days, the lymphocytes should have died, reducing the risk of TA-GVHD ^[16].

Patients should be placed in reverse-barrier isolation ^[3]^[4]

Measure	Detail	Rationale
Reverse-barrier isolation	Patient in a single room; healthcare workers gown, glove, mask before entering	Protects the patient FROM the environment (opposite of contact isolation which protects the environment from the patient)
Hand hygiene	Alcohol hand rub before and after patient contact	Single most effective infection prevention measure
Face mask	Patient wears mask when leaving room; visitors screened for illness	Reduces airborne pathogen exposure
HEPA filtration / positive pressure rooms	HSCT recipients should be placed in rooms with positive pressure and high-efficiency particulate air (HEPA) filtration ^[3]^[4]	Positive pressure prevents unfiltered corridor air from entering the room; HEPA filters remove Aspergillus spores (3–5 µm)
No plants or flowers	Plants and dried or fresh flowers should not be allowed in hospital rooms of neutropenic patients ^[3]^[4]	Soil and stagnant water harbour Aspergillus and other moulds
Low-bacterial diet	Low-microbial diet consisting of well-cooked food ^[3]^[4]	Avoids raw foods that may carry Gram-negative bacteria, Listeria, Salmonella; often instituted but may not reduce occurrence of infection or fever ^[3]^[4]

Product	Trigger	Target
Packed RBCs	Hb < 70 g/L (or < 80 g/L if symptomatic / cardiac disease)	Correct anaemia from marrow suppression
Platelets	PLT < 10 × 10⁹/L (prophylactic) or < 20 if febrile / bleeding	Prevent/treat haemorrhage
FFP / Cryoprecipitate	DIC with active bleeding or PT/APTT > 1.5× normal	Correct coagulopathy

VIII. Prevention of Neutropenic Fever

Prevention is divided into antimicrobial prophylaxis and growth factor prophylaxis.

Type	Agent	Indication	Mechanism / Rationale
Antibacterial prophylaxis	Levofloxacin 500mg QD PO ^[3]^[4]	High-risk neutropenic patients (expected ANC < 0.5 for > 7 days)	Effectively reduces febrile events and invasive Gram-negative infections ^[3]^[4]; fluoroquinolones have excellent bioavailability and broad Gram-negative cover. Disadvantage: selects for fluoroquinolone-resistant organisms and does not cover Gram-positives
Antifungal prophylaxis	Posaconazole 300mg QD PO or Fluconazole 200–400mg QD PO	Prolonged and profound neutropenia; HSCT recipients; AML induction chemotherapy ^[2]	Reduces invasive candidiasis (fluconazole) and both candidiasis + aspergillosis (posaconazole); posaconazole preferred for AML/MDS patients as it also covers Aspergillus
Antiviral prophylaxis	Aciclovir 400mg BD PO or Valaciclovir 500mg QD–BD	HSV/VZV seropositive patients undergoing intensive chemotherapy or HSCT	Prevents herpesvirus reactivation (HSV mucositis, VZV shingles) during immunosuppression
PJP prophylaxis	Co-trimoxazole (TMP-SMX) 480mg QD or 960mg 3 times/week	Patients on prolonged steroids, purine analogues (fludarabine), alemtuzumab, temozolomide, post-HSCT	Prevents Pneumocystis jirovecii pneumonia; most effective prophylactic agent; check G6PD first

Azathioprine and Neutropenic Fever — Exam Pearl

Azathioprine can cause neutropenic fever if metabolised excessively to the toxic metabolite 6-TGTP ^[17]. Before starting azathioprine:

Check TPMT enzyme activity — low TPMT → excess 6-MP → toxicity
Check NUDT15 enzyme activity — more common in HK/Asian populations → excess 6-TGTP → severe myelosuppression
Check if the patient is taking xanthine oxidase inhibitors (allopurinol, febuxostat) — XO is crucial for converting 6-MP to inactive metabolites; inhibition → drug accumulation → bone marrow toxicity

A patient with IBD or autoimmune disease who develops neutropenic fever on azathioprine is a common exam scenario.

Colony stimulating factors ^[3]^[4]:

Agent	Indication for PRIMARY Prophylaxis	Timing
G-CSF (filgrastim 5 µg/kg/day SC or pegfilgrastim 6mg SC single dose)	Chemotherapy regimen with ≥ 20% risk of febrile neutropenia (e.g. dose-dense regimens, CHOP-14 for lymphoma)	Start 24–72 hours after completion of chemotherapy; continue until ANC recovery > 1.0
Secondary prophylaxis	Patient who experienced neutropenic fever in a prior chemotherapy cycle and dose reduction is not acceptable	Same timing as above

Why not give G-CSF to everyone? In regimens with < 10% risk of febrile neutropenia, the cost and side effects (bone pain, rarely splenic rupture, leukaemoid reaction) outweigh the benefit. For regimens with 10–20% risk, consider if patient has additional risk factors (age > 65, poor performance status, prior febrile neutropenia).

IX. Special Management Scenarios

Decision	When	Action
Catheter salvage (try to keep the line)	CoNS, Enterococcus, Gram-negative (non-complicated); tunnel tract infection absent; patient clinically stable	Antibiotic lock therapy (instilling concentrated antibiotic into the catheter lumen for 8–12 hours) + systemic antibiotics
Catheter removal (must remove the line)	S. aureus, Candida spp., Pseudomonas, mycobacteria, tunnel tract infection, persistent bacteraemia > 72h despite appropriate antibiotics, haemodynamic instability, septic emboli	Remove catheter + systemic antibiotics (S. aureus CRBSI → minimum 14 days IV antibiotics after line removal; Candida → 14 days after last positive culture)

Aspect	Management
Medical	Bowel rest (NBM), IV fluids, broad-spectrum antibiotics with anaerobic cover (Tazocin or carbapenem + metronidazole), G-CSF consideration
Surgical	Indicated for: perforation, uncontrolled haemorrhage, clinical deterioration despite maximal medical therapy; surgery carries very high mortality in neutropenic patients — avoid if possible

Phase	Agent	Duration
Primary therapy	Voriconazole (preferred) or isavuconazole	≥ 6–12 weeks minimum; continue until clinical and radiological resolution + immune recovery
Salvage therapy	L-AmB, posaconazole, caspofungin (combination)	For refractory or intolerant patients
Surgical	Resection of localised pulmonary lesion if adjacent to great vessels and risk of haemorrhage	Debulk large lesions or prevent fatal haemoptysis

Phase	Action	Key Agents
Immediate (0–1 hour)	Blood cultures → empirical IV broad-spectrum Abx	Tazocin / Cefepime / Meropenem ± Gentamicin ± Vancomycin
48–72 hours	Reassess: culture results, clinical response	Targeted therapy if culture positive; continue empirical if culture negative and improving
Day 4–7	Persistent fever? Add antifungal	Caspofungin / L-AmB / Voriconazole
Ongoing	Duration: treat until afebrile ≥ 48h + ANC > 0.5; or complete standard course if source identified	Minimum 7 days; 14 days if source identified
Supportive	G-CSF (selected), buffy coat (refractory), reverse isolation, transfusion support	Filgrastim; irradiated WBC transfusion; packed RBCs, platelets
Prevention	Prophylaxis for high-risk patients	Levofloxacin (antibacterial), posaconazole/fluconazole (antifungal), aciclovir (antiviral), co-trimoxazole (PJP)

High Yield Summary — Management of Neutropenic Fever

Immediate:

Blood cultures (CVC + peripheral) → empirical IV anti-pseudomonal antibiotics WITHIN 1 HOUR
First-line: IV Tazocin 4.5g Q6–8h (HK practice)
Add aminoglycoside if haemodynamically unstable; add vancomycin only for specific indications (MRSA, line sepsis, skin infection, pneumonia)

At 48–72 hours:

Culture positive → targeted therapy
Culture negative + improving → continue
Culture negative + persistent fever → reassess; repeat cultures, CT thorax, fungal markers

Day 4–7 persistent fever:

Add empirical antifungal: caspofungin or L-AmB or voriconazole

Duration:

Known source: complete standard course (14 days)
Unknown source: continue until afebrile ≥ 48h AND ANC > 0.5 × 10⁹/L
Minimum 7 days

Supportive:

G-CSF: NOT routine; consider in septic shock, fungal infection, severe pneumonia
Buffy coat: ANC < 0.5 + documented infection not responding to Abx + antifungal for ≥ 48h; must be irradiated
Reverse isolation, hand hygiene, HEPA filtration for HSCT, no plants/flowers, low-bacterial diet

Prevention:

Levofloxacin prophylaxis for high-risk patients (reduces Gram-negative infections)
Posaconazole/fluconazole for antifungal prophylaxis
Aciclovir for antiviral prophylaxis
Co-trimoxazole for PJP prophylaxis (check G6PD first)
G-CSF primary prophylaxis if chemotherapy regimen has ≥ 20% risk of febrile neutropenia

Active Recall - Management of Neutropenic Fever

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 423–424, Complications of Leukemia — Neutropenic Fever) ^[2] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p. 9, Supportive treatment of acute leukemia) ^[3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 1332, Neutropenic fever — Treatment and Prevention) ^[4] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 575, Neutropenic fever — Treatment and Prevention) ^[5] Senior notes: Maksim Medicine Notes.pdf (p. 49, Neutropenic fever — Management) ^[6] Senior notes: Ryan Ho Haemtology.pdf (p. 71, Neutropenic Fever — Management) ^[9] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf (p. 8, Approach to Mx of neutropenic fever) ^[13] Senior notes: Learning_Points_All_Lectures.txt (Learning Point 3 — febrile neutropenia as medical emergency) ^[16] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (p. 5, 8, 22, Leukocytes / Buffy coat, Irradiated blood products) ^[17] Senior notes: Block A - Chronic diarrhoea_ irritable bowel syndrome and inflammatory bowel disease.pdf (p. 45, Azathioprine — TPMT, NUDT15, XO inhibitors)

Complications of Neutropenic Fever

Complications of neutropenic fever span a wide spectrum — from the immediate life-threatening consequences of uncontrolled infection to the iatrogenic consequences of the treatments themselves, to the paradoxical syndromes that arise when the immune system recovers. Understanding these from first principles helps you anticipate, recognise, and manage them.

I. Complications of the Infection Itself

This is the most feared and most immediately lethal complication.

Aspect	Detail
Pathophysiology	Unchecked proliferation of bacteria can lead to rapid progression into septic shock, especially in Gram-negative sepsis ^[1]. Gram-negative endotoxin (LPS) activates TLR4 on macrophages → massive release of TNF-α, IL-1β, IL-6 → systemic vasodilation (↓SVR) + capillary leak (fluid shifts from intravascular to interstitial space) + myocardial depression → distributive shock. Without neutrophils to contain the infection at its source, the bacterial load in the blood escalates exponentially.
Mortality	~50% if septic shock develops (compared to ~11% overall for neutropenic fever) ^[5]
Clinical features	Hypotension (SBP < 90 mmHg or MAP < 65 mmHg) refractory to fluid resuscitation, tachycardia, warm peripheries initially (distributive shock) → cold peripheries later (decompensation), oliguria, altered consciousness, rising lactate > 2 mmol/L
Why is it worse in neutropenic patients?	In immunocompetent patients, neutrophils localise and contain infection early. In neutropenic patients, there is no containment — bacteria disseminate freely from the primary site (gut, catheter, lung) into the bloodstream. By the time hypotension develops, the bacterial burden is already overwhelming.
Management	Sepsis-3 bundle: IV crystalloid 30 mL/kg, vasopressors (noradrenaline) if MAP < 65, empirical broad-spectrum antibiotics within 1 hour, lactate monitoring Q2–4h, source control

Aspect	Detail
Pathophysiology	Severe sepsis (especially Gram-negative) → massive tissue factor release + endothelial damage → simultaneous activation of coagulation cascade throughout the vasculature → consumption of clotting factors and platelets → microthrombi in small vessels (organ ischaemia) + paradoxical bleeding (consumptive coagulopathy). In acute promyelocytic leukaemia (APML/APL), the granules of malignant promyelocytes themselves contain pro-coagulant and fibrinolytic substances → DIC even before chemotherapy ^[13].
Clinical features	Bleeding from multiple sites (venepuncture sites, mucosal surfaces, GI tract), petechiae, purpura, acral ischaemia (fingertip gangrene), organ dysfunction
Lab findings	↑PT/INR, ↑APTT, ↓fibrinogen, ↑D-dimer, ↓platelets, fragmented RBCs (schistocytes) on peripheral blood smear
Management	Treat the underlying cause (infection/leukaemia); supportive: platelet transfusion (target > 50 if bleeding), cryoprecipitate (target fibrinogen > 1.0 g/L), FFP (if PT/APTT > 1.5× normal with bleeding)

Organ	Mechanism in Sepsis	Clinical Manifestation
Kidneys	Hypoperfusion + direct endotoxin injury → acute tubular necrosis (ATN)	Oliguria, rising creatinine, metabolic acidosis; may require renal replacement therapy
Lungs	Capillary leak + neutrophil-mediated (paradoxically, even in neutropenic patients, small numbers of remaining immune cells + complement activation can cause endothelial damage) → ARDS	Bilateral infiltrates on CXR, refractory hypoxaemia (PaO₂/FiO₂ < 300), need for mechanical ventilation
Liver	"Shock liver" — hepatocyte ischaemia from hypoperfusion	Massively elevated ALT/AST (often > 1000 U/L), rising bilirubin, coagulopathy
CNS	Septic encephalopathy — microabscesses, cerebral oedema, metabolic derangement	Confusion, agitation, obtundation, coma
Heart	Septic cardiomyopathy — direct myocardial depression by TNF-α and IL-1β	↓EF on echocardiography, elevated troponin, haemodynamic deterioration

Why does organ failure beget more organ failure? Each failing organ compounds the insult to others. For example, AKI → fluid overload and metabolic acidosis → worsens cardiac function → worsens renal perfusion. This vicious cycle is why septic shock with MODS carries such high mortality.

When bacteraemia is not contained, organisms can seed distant sites:

Complication	Organism	Pathophysiology	Clinical Clue
Infective endocarditis	S. aureus, viridans streptococci, enterococci	Bacterial seeding of cardiac valves (especially if pre-existing valvular abnormality or prosthetic valve) → vegetation formation	Persistent bacteraemia (S. aureus > 48–72h despite antibiotics), new murmur, embolic phenomena (splinter haemorrhages, Janeway lesions)
Cerebral abscess / meningitis	Gram-negatives, fungi (Aspergillus, Cryptococcus), Toxoplasma	Haematogenous spread to CNS; or direct extension from sinusitis (Aspergillus, Mucor)	Headache, altered consciousness, focal neurology, seizures; CT showing ring-enhancing lesion or meningeal enhancement
Hepatosplenic candidiasis	Candida spp.	Disseminated candidiasis seeds liver and spleen → microabscesses; classically becomes symptomatic as neutrophils recover ("unmasking")	Persistent fever during neutrophil recovery, ↑ALP, "bull's-eye" lesions on CT/MRI liver and spleen
Osteomyelitis / septic arthritis	S. aureus, Gram-negatives	Haematogenous seeding of bone/joints	Bone pain, joint swelling; MRI is best diagnostic modality
Mycotic aneurysm	S. aureus, Salmonella	Bacterial infection of arterial wall → weakening → aneurysm formation → rupture	Pulsatile mass, sudden haemodynamic collapse

II. Site-Specific Infectious Complications

Aspect	Detail
Definition	Necrotising inflammation of the caecum (and sometimes other bowel segments) in a neutropenic patient
Pathophysiology	Chemotherapy damages caecal mucosa → mucosal breakdown → bacterial invasion of the bowel wall → transmural inflammation ± necrosis. The caecum is most vulnerable because it has the thinnest wall and poorest blood supply in the large bowel.
Clinical features	RIF pain, diarrhoea (± bloody), abdominal distension, fever; signs may be subtle due to neutropenia
Diagnosis	CT abdomen: caecal wall thickening ( > 4mm), pericolonic fat stranding, ± intramural gas (pneumatosis intestinalis)
Complications	Perforation → faecal peritonitis → septic shock; haemorrhage; stricture (late)
Management	Medical: bowel rest (NBM), IV fluids, broad-spectrum antibiotics with anaerobic cover, G-CSF consideration. Surgical: only for perforation, uncontrolled haemorrhage, or clinical deterioration despite maximal medical therapy — surgery carries extremely high mortality in neutropenic patients

Aspect	Detail
When	Prolonged neutropenia ( > 7 days); haematological malignancy; post-HSCT ^[1]^[7]
Pathophysiology	Aspergillus spores (ubiquitous in the environment) are inhaled → normally cleared by alveolar macrophages and neutrophils. In neutropenia, spores germinate into hyphae → angioinvasion (Aspergillus hyphae have a tropism for blood vessels) → thrombosis → tissue infarction and necrosis → haemorrhagic infarct
Clinical features	Persistent fever despite broad-spectrum antibiotics, pleuritic chest pain, haemoptysis
Imaging	CT thorax: halo sign (early — ground-glass halo around nodule representing haemorrhage) → air-crescent sign (late — crescent of air as necrotic tissue separates at neutrophil recovery)
Complications	Fatal haemoptysis (if fungal nodule erodes into a major pulmonary artery), dissemination to brain (cerebral aspergillosis — brain abscess), skin, other organs
Mortality	30–60% even with treatment; higher in disseminated disease

Aspect	Detail
Pathophysiology	Fungal spores colonise the sinuses → invade through sinus mucosa and bone → extension to orbits and brain (rhinocerebral mucormycosis)
Clinical clue	Facial pain, nasal discharge (often bloody), necrotic black eschar on palate or nasal turbinates (pathognomonic), proptosis, cranial nerve palsies
Urgency	Surgical emergency — requires urgent surgical debridement of necrotic tissue + high-dose L-AmB. Delay is fatal.

Aspect	Detail
Why in neutropenic fever?	Broad-spectrum antibiotics (especially the first-line agents used empirically) disrupt normal colonic flora → C. difficile overgrowth → toxin production (toxins A and B) → mucosal inflammation and necrosis
Clinical features	Watery diarrhoea (may be bloody), abdominal pain, fever; may be masked by neutropenia
Diagnosis	Stool for C. difficile cytotoxin and culture ^[9] or stool PCR for toxin genes
Complications	Toxic megacolon (colonic dilation > 6 cm with systemic toxicity), perforation, peritonitis
Treatment	Oral vancomycin 125mg Q6h PO (first-line) or fidaxomicin 200mg BD PO; severe/fulminant: add IV metronidazole 500mg Q8h; colectomy for toxic megacolon with perforation

III. Complications of Treatment (Iatrogenic)

Complication	Causative Agent	Mechanism	Clinical Features
Nephrotoxicity	Aminoglycosides (gentamicin, amikacin), amphotericin B (conventional > liposomal), vancomycin	Aminoglycosides accumulate in proximal tubular cells → direct tubular injury; amphotericin B causes renal vasoconstriction + direct tubular toxicity; vancomycin at high troughs damages tubules	Rising creatinine, oliguria, electrolyte wasting (Mg²⁺, K⁺ with amphotericin B); monitor drug levels and renal function
Ototoxicity	Aminoglycosides	Accumulate in cochlear and vestibular hair cells → irreversible damage	Hearing loss (high-frequency first), tinnitus, vertigo; often irreversible
C. difficile colitis	Any broad-spectrum antibiotic (especially fluoroquinolones, clindamycin, cephalosporins)	Disruption of colonic microbiome → C. difficile overgrowth	Diarrhoea, fever, abdominal pain (see above)
Drug fever	Beta-lactams, vancomycin, amphotericin B	Hypersensitivity or direct pyrogenicity	Persistent fever that resolves on drug cessation; may be accompanied by eosinophilia or rash
Hepatotoxicity	Voriconazole, isoniazid (if TB treatment), co-trimoxazole	Drug-induced liver injury (DILI)	Elevated ALT/AST, jaundice; requires LFT monitoring
Visual disturbances	Voriconazole	Transient inhibition of retinal function (mechanism not fully elucidated; related to drug binding to visual pigments)	Photopsia (flashes of light), altered colour perception, blurred vision; reversible; occurs in ~30% of patients
Photosensitivity	Voriconazole (long-term)	UVA-induced phototoxicity → risk of skin malignancy (squamous cell carcinoma) with prolonged use	Exaggerated sunburn, erythema; counsel on sun avoidance and photoprotection
Bone marrow suppression	Co-trimoxazole, ganciclovir (for CMV), linezolid	Folate antagonism (co-trimoxazole), direct myelotoxicity (ganciclovir, linezolid)	Worsened cytopaenia — the very problem you are trying to manage
QT prolongation	Fluoroquinolones, azole antifungals (voriconazole, fluconazole), macrolides	Block cardiac hERG potassium channels → delayed ventricular repolarisation	Risk of torsades de pointes; perform baseline ECG; avoid combining QT-prolonging agents

Azathioprine-Induced Neutropenic Fever

A patient with atopic dermatitis died of neutropenic fever after being on azathioprine ^[17]. This is a cautionary tale from HK clinical practice. Azathioprine-induced myelosuppression is predictable and preventable — always check TPMT and NUDT15 enzyme activity before prescribing, and check for concomitant xanthine oxidase inhibitors (allopurinol, febuxostat) ^[17].

Given that neutropenic patients require frequent transfusions (packed RBCs for anaemia, platelets for thrombocytopaenia, buffy coat for refractory infections), transfusion-related complications are common:

Complication	Mechanism	Clinical Features	Prevention
Febrile non-haemolytic transfusion reaction (FNHTR)	Cytokines from residual leucocytes in blood products; most common transfusion reaction ^[16]	Fever, chills during or after transfusion; patient otherwise well	Use leucodepleted products; pre-medication with paracetamol
Transfusion-associated graft-versus-host disease (TA-GVHD)	Donor lymphocytes in non-irradiated blood products attack recipient tissues; almost universally fatal in immunocompromised patients ^[16]	Fever, maculopapular rash, diarrhoea, liver dysfunction, pancytopaenia; onset 1–6 weeks post-transfusion	Blood products must be irradiated for immunocompromised patients ^[16] to eliminate donor lymphocytes
Transfusion-related acute lung injury (TRALI)	Anti-HLA or anti-neutrophil antibodies in donor plasma activate recipient neutrophils in the pulmonary vasculature → capillary leak → non-cardiogenic pulmonary oedema	Acute respiratory distress within 6 hours of transfusion; bilateral infiltrates on CXR; hypoxia	Use male-only plasma donors (reduces anti-HLA antibodies from multiparous female donors)
Iron overload (haemosiderosis)	Chronic transfusions → each unit of packed RBCs contains ~250 mg iron; body has no active excretion mechanism for iron	Organ damage: cardiomyopathy, liver cirrhosis, endocrine dysfunction (DM, hypogonadism)	Iron chelation therapy (deferasirox, deferoxamine) if ferritin > 1000 or > 20 units transfused
Bacterial contamination of blood products	Bacteria (especially in platelet concentrates stored at room temperature)	High fever, rigors, hypotension shortly after starting transfusion	Bacterial screening of platelet products; pathogen reduction technology

Emergency — No Irradiated Blood Available

If irradiated products are unavailable in an emergency: ask the blood bank for the oldest bag of blood — after > 14 days of storage, donor lymphocytes should have died, reducing TA-GVHD risk ^[16].

Indwelling central venous catheters (Hickman, PICC, port) are essential for chemotherapy delivery but are a double-edged sword:

Complication	Mechanism	Management
Catheter-related bloodstream infection (CRBSI)	Biofilm formation on catheter surface by skin commensals (CoNS, S. aureus) or gut-translocated organisms; bacteria seed into bloodstream	Antibiotic lock therapy ± systemic antibiotics; catheter removal for S. aureus, Candida, Pseudomonas, tunnel infection, or persistent bacteraemia > 72h
Catheter-related thrombosis	Foreign body in vein → endothelial damage + stasis → Virchow's triad → DVT of subclavian/internal jugular vein	Anticoagulation (LMWH → warfarin or DOAC); catheter removal if extensive thrombus or no longer needed
Mechanical complications	Pneumothorax (at insertion), catheter fracture, air embolism, catheter tip malposition	Procedural precautions; CXR post-insertion

IV. Immune Reconstitution Syndromes

These are paradoxical complications that occur when the immune system recovers, not when it is suppressed. They are increasingly recognised and can be confusing to the uninitiated.

Paradoxical deterioration with fever and a new inflammatory focus or progression of a preexisting inflammatory focus can happen in temporal relationship to the recovery of the immune defect ^[18]

Aspect	Detail
Examples of immune recovery triggers	Recovery of CD4 lymphocyte count after antiretroviral treatment (HIV-related IRIS); recovery of ANC after chemotherapy (Myeloid Reconstitution Syndrome) ^[18]
Pathophysiology	During profound immunosuppression, subclinical infections exist but cannot mount an inflammatory response (hence "occult" — no symptoms, no imaging findings). When the immune system recovers (ANC rises, CD4 count rises), it suddenly "sees" these pathogens and mounts a vigorous inflammatory response → paradoxical clinical worsening despite the infection itself not spreading
Clinical features	New fever during neutrophil recovery, new or worsening pulmonary infiltrates, new lymphadenopathy, worsening of skin lesions, worsening of hepatosplenic candidiasis (previously occult microabscesses now become visible on imaging as neutrophils infiltrate them)
Classic examples	Hepatosplenic candidiasis unmasked at neutrophil recovery; mycobacterial IRIS (paradoxical TB worsening); Aspergillus IRIS (enlarging pulmonary nodules despite adequate antifungal therapy and rising ANC)
Management	Distinguish from true treatment failure — the key clue is that IRIS occurs at the time of immune recovery, not at nadir. Continue antimicrobials; consider short-course corticosteroids if inflammatory response is life-threatening (e.g. worsening respiratory failure); do NOT escalate antifungals/antibiotics unnecessarily

IRIS vs Treatment Failure — How to Tell the Difference

Feature	IRIS	Treatment Failure
Timing	At immune recovery (rising ANC or CD4)	At nadir or during persistent immunosuppression
Cultures	Usually negative (pathogen being cleared)	May be positive (pathogen persisting or new pathogen)
Response to escalating antimicrobials	No improvement (it's inflammation, not infection)	Improvement with broader coverage
Response to corticosteroids	Improvement	Worsening (immunosuppression potentiates infection)

Aspect	Detail
Context	Post-HSCT, specifically around the time of neutrophil engraftment (ANC > 0.5 for 3 consecutive days, typically Day 10–14 post-autologous HSCT, Day 14–21 post-allogeneic HSCT)
Pathophysiology	Newly produced neutrophils and monocytes release cytokines (IL-1, IL-6, TNF-α, GM-CSF) in an exuberant, dysregulated manner → capillary leak, tissue inflammation
Clinical features	Non-infectious fever, skin rash (erythematous, maculopapular), non-cardiogenic pulmonary oedema (capillary leak → bilateral infiltrates), diarrhoea, weight gain (fluid retention); can mimic acute GVHD
Distinction from acute GVHD	Engraftment syndrome occurs earlier (at engraftment), responds to corticosteroids, and is self-limiting. GVHD occurs later and involves specific target organs (skin, liver, gut) with histological confirmation.
Management	Corticosteroids (methylprednisolone 1–2 mg/kg/day); supportive care; resolves within days

V. Complications of Prolonged Neutropenia

Aspect	Detail
Why it occurs	Prolonged empirical broad-spectrum antibiotics exert selective pressure → resistant organisms survive and proliferate. Key resistant phenotypes in HK: ESBL-producing Enterobacterales, carbapenem-resistant organisms (CRO), MRSA, VRE, multi-drug resistant Pseudomonas
Clinical consequence	Subsequent episodes of neutropenic fever may be caused by organisms resistant to the standard empirical regimen → higher mortality, need for "last-resort" agents (colistin, tigecycline)
Prevention	Antibiotic stewardship: de-escalate when possible, narrow spectrum when culture results available, avoid unnecessarily prolonged courses

Aspect	Detail
Risk	Each chemotherapy cycle carries risk of neutropenic fever; patients receiving multiple cycles may have recurrent episodes, each potentially caused by different (and increasingly resistant) organisms
Impact	Cumulative organ toxicity from repeated antibiotic courses (nephrotoxicity, C. difficile), psychological burden, chemotherapy delays (dose reductions or cycle postponement to allow marrow recovery)
Prevention	G-CSF prophylaxis for regimens with ≥ 20% risk; consider dose reduction or alternative regimen if recurrent life-threatening episodes

Aspect	Detail
Why it matters	Neutropenic fever may necessitate postponement of the next chemotherapy cycle until the patient recovers → delays in treatment → potentially compromised oncological outcomes (reduced cure rates, higher relapse rates)
Balance	The oncologist must weigh the risk of treatment delay against the risk of another episode; G-CSF secondary prophylaxis or dose reduction may be employed to maintain treatment intensity

Category	Specific Complications	Key Mechanism	Mortality / Severity
Sepsis / Shock	Septic shock, DIC, MODS	Endotoxin → cytokine storm → vasodilation, capillary leak, organ damage	~50% mortality in septic shock ^[5]
Metastatic infection	Endocarditis, brain abscess, hepatosplenic candidiasis, osteomyelitis	Haematogenous seeding from primary bacteraemia / fungaemia	Variable; endocarditis and brain abscess carry high mortality
Site-specific	Typhlitis, IPA, fungal sinusitis, C. difficile colitis	Mucosal damage + neutropenia → local invasion; antibiotic-induced dysbiosis	Typhlitis: perforation → high mortality; IPA: 30–60% mortality
Drug-related	Nephrotoxicity, ototoxicity, hepatotoxicity, C. difficile, drug fever, bone marrow suppression, QT prolongation	Direct organ toxicity or hypersensitivity	Usually manageable if recognised early
Transfusion-related	FNHTR, TA-GVHD, TRALI, iron overload, bacterial contamination	Immune-mediated or infectious	TA-GVHD: almost universally fatal
Vascular access	CRBSI, catheter thrombosis	Biofilm, endothelial injury	CRBSI: significant morbidity; thrombosis: PE risk
Immune reconstitution	IRIS / Myeloid Reconstitution Syndrome, engraftment syndrome	Paradoxical inflammatory response at immune recovery	Variable; can be fatal if misdiagnosed as treatment failure
Antimicrobial resistance	MDR organisms	Selective pressure from prolonged antibiotics	Higher mortality in subsequent infections
Oncological	Delayed chemotherapy, dose reduction	Neutropenic fever necessitates treatment postponement	Potentially compromised cure rates

High Yield Summary — Complications of Neutropenic Fever

Infection-related:

Septic shock (mortality ~50%) — especially Gram-negative endotoxic shock
DIC — consumptive coagulopathy; bleeding + thrombosis simultaneously
MODS — kidneys, lungs, liver, CNS, heart
Metastatic infection — endocarditis, brain abscess, hepatosplenic candidiasis

Site-specific:

Neutropenic enterocolitis (typhlitis) — RIF pain, caecal wall thickening, risk of perforation
Invasive pulmonary aspergillosis — halo sign, angioinvasion, haemoptysis, high mortality
C. difficile colitis — antibiotic-induced; risk of toxic megacolon
Invasive fungal sinusitis — surgical emergency

Treatment-related:

Nephrotoxicity (aminoglycosides, amphotericin B, vancomycin)
TA-GVHD from non-irradiated blood products — almost universally fatal; irradiate all products for immunocompromised patients
C. difficile from broad-spectrum antibiotics

Immune reconstitution:

IRIS / Myeloid Reconstitution Syndrome — paradoxical worsening at ANC recovery; distinguish from treatment failure
Engraftment syndrome — non-infectious fever + rash + pulmonary oedema at HSCT engraftment; responds to steroids

Systemic:

Antimicrobial resistance from prolonged empirical antibiotics
Delayed chemotherapy → potentially compromised oncological outcomes

Active Recall - Complications of Neutropenic Fever

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 423, Complications of Leukemia — Neutropenic Fever) ^[5] Senior notes: Maksim Medicine Notes.pdf (p. 49, Clinical oncology — Neutropenic fever) ^[7] AOS material: AOS - Microbio.pdf (p. 5, Neutropenic fever pathogens) ^[9] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf (p. 8, Approach to Mx) ^[13] Senior notes: Learning_Points_All_Lectures.txt (Learning Point 2 — APML and DIC; Learning Point 3 — febrile neutropenia as medical emergency) ^[16] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (p. 5, 8, 22, Leukocytes / Buffy coat, TA-GVHD, Irradiated products) ^[17] Senior notes: Block A - Treatments for skin diseases (eczema, psoriasis and urticaria).pdf (p. 23, Azathioprine and neutropenic fever) ^[18] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts [Handout].pdf (p. 6, IRIS / Myeloid Reconstitution Syndrome, Prevention of infections)

High Yield Summary

Definition:

Neutropenic fever = ANC ≤ 0.5 × 10⁹/L (or ≤ 1.0 with predicted decline to ≤ 0.5 in 48h) + single oral temp ≥ 38.3°C or sustained ≥ 38.0°C for ≥ 1 hour

Key Numbers:

Occurs in 10–50% of solid tumours; higher in haematological malignancies
Only 20–30% are culture-positive
Mortality ~11% overall, ~50% with septic shock
Nadir: Day 7–10 (Taxanes D4–5; post-HSCT D21)
Neutrophil lifespan: ~2–3 days

Risk Factors: Duration and depth of neutropenia are most important; prolonged ( ≥ 7 days) and profound ( < 0.1) = highest risk

Pathogens:

Gram-positive now most common (CoNS, S. aureus, viridans strep) — due to catheters
Gram-negative most dangerous (Pseudomonas, E. coli) — endotoxin → septic shock
Fungal (Candida, Aspergillus) — with prolonged neutropenia > 7 days
Viral reactivation (HSV, VZV, CMV)

Clinical Features:

Fever is often the ONLY sign
Pus is NOT formed (no neutrophils)
CXR may be normal despite pneumonia
Examine: skin, oral cavity, lungs, abdomen, perianal area, catheter sites, BM biopsy sites, sinuses — DAILY
Avoid DRE

Principle: Medical emergency — start empirical broad-spectrum anti-pseudomonal antibiotics within 1 hour of presentation

High Yield Summary — Differential Diagnosis of Neutropenic Fever

Primary concern is always INFECTION — treat empirically before the pathogen is identified.

Infectious causes:

Bacteria are most common; Gram-positive now more frequent (catheter-related), but Gram-negative most dangerous (endotoxic shock)
Fungi emerge with prolonged neutropenia > 7 days (Aspergillus, Candida)
Viruses — herpesvirus reactivation (HSV, VZV, CMV) and respiratory viruses
TB — always consider in HK (endemic); extrapulmonary presentations

Non-infectious causes (consider when fever persists despite adequate antibiotics):

Drug fever (temporal correlation, "looks well")
Tumour fever (positive naproxen test)
Transfusion reaction (exclude ABO incompatibility first)
GVHD (post-HSCT: rash + diarrhoea + liver dysfunction)
VTE / PE
Engraftment syndrome

Clinical approach by site: Examine skin, oral cavity, lungs, abdomen, perianal area, catheter sites, BM biopsy sites, and sinuses — DAILY

Temporal pattern: Day 7–14 = bacteria at nadir; > 7 days neutropenia = fungi; recovery phase = engraftment syndrome / unmasking

High Yield Summary — Diagnosis and Investigations

Diagnostic Criteria:

ANC ≤ 0.5 (or ≤ 1.0 with predicted decline to ≤ 0.5 in 48h) + Temp ≥ 38.3°C single or ≥ 38.0°C for ≥ 1h
Clinical diagnosis — does NOT require positive culture

Risk Stratification:

MASCC score ≥ 21 = low risk; < 21 = high risk
High risk if: prolonged neutropenia ≥ 7 days, profound ANC < 0.1, haemodynamic instability, organ dysfunction

Key Investigations:

Blood cultures FIRST (CVC two ports + peripheral) → then antibiotics within 1 hour
Baseline: CBP d/c, LRFT, CaPO₄, lactate, coag, ABG
CXR for all; CT thorax for high risk or symptomatic (look for halo sign)
CT abdomen for abdominal symptoms (typhlitis, C. diff colitis)
Stool C. difficile toxin/PCR if diarrhoea
Serial galactomannan + β-D-glucan if persistent fever > 4–7 days
Directed cultures: urine, sputum, skin swab, BAL, CSF as clinically indicated

Pitfalls:

Normal CXR does NOT exclude pneumonia (no neutrophils to form infiltrate)
Absent pyuria does NOT exclude UTI
Paucity of CSF pleocytosis does NOT exclude meningitis
Galactomannan falsely positive with piperacillin-tazocin

High Yield Summary — Management of Neutropenic Fever

Immediate:

Blood cultures (CVC + peripheral) → empirical IV anti-pseudomonal antibiotics WITHIN 1 HOUR
First-line: IV Tazocin 4.5g Q6–8h (HK practice)
Add aminoglycoside if haemodynamically unstable; add vancomycin only for specific indications (MRSA, line sepsis, skin infection, pneumonia)

At 48–72 hours:

Culture positive → targeted therapy
Culture negative + improving → continue
Culture negative + persistent fever → reassess; repeat cultures, CT thorax, fungal markers

Day 4–7 persistent fever:

Add empirical antifungal: caspofungin or L-AmB or voriconazole

Duration:

Known source: complete standard course (14 days)
Unknown source: continue until afebrile ≥ 48h AND ANC > 0.5 × 10⁹/L
Minimum 7 days

Supportive:

G-CSF: NOT routine; consider in septic shock, fungal infection, severe pneumonia
Buffy coat: ANC < 0.5 + documented infection not responding to Abx + antifungal for ≥ 48h; must be irradiated
Reverse isolation, hand hygiene, HEPA filtration for HSCT, no plants/flowers, low-bacterial diet

Prevention:

Levofloxacin prophylaxis for high-risk patients (reduces Gram-negative infections)
Posaconazole/fluconazole for antifungal prophylaxis
Aciclovir for antiviral prophylaxis
Co-trimoxazole for PJP prophylaxis (check G6PD first)
G-CSF primary prophylaxis if chemotherapy regimen has ≥ 20% risk of febrile neutropenia

High Yield Summary — Complications of Neutropenic Fever

Infection-related:

Septic shock (mortality ~50%) — especially Gram-negative endotoxic shock
DIC — consumptive coagulopathy; bleeding + thrombosis simultaneously
MODS — kidneys, lungs, liver, CNS, heart
Metastatic infection — endocarditis, brain abscess, hepatosplenic candidiasis

Site-specific:

Neutropenic enterocolitis (typhlitis) — RIF pain, caecal wall thickening, risk of perforation
Invasive pulmonary aspergillosis — halo sign, angioinvasion, haemoptysis, high mortality
C. difficile colitis — antibiotic-induced; risk of toxic megacolon
Invasive fungal sinusitis — surgical emergency

Treatment-related:

Nephrotoxicity (aminoglycosides, amphotericin B, vancomycin)
TA-GVHD from non-irradiated blood products — almost universally fatal; irradiate all products for immunocompromised patients
C. difficile from broad-spectrum antibiotics

Immune reconstitution:

IRIS / Myeloid Reconstitution Syndrome — paradoxical worsening at ANC recovery; distinguish from treatment failure
Engraftment syndrome — non-infectious fever + rash + pulmonary oedema at HSCT engraftment; responds to steroids

Systemic:

Antimicrobial resistance from prolonged empirical antibiotics
Delayed chemotherapy → potentially compromised oncological outcomes

Neutropenic Fever

1. Definition

2. Epidemiology

3. Risk Factors

3.1 Neutrophil-Related Factors

3.2 Treatment-Related Factors

3.3 Patient-Related Factors

4. Anatomy and Function: Why Neutrophils Are the Key Players

4.1 Neutrophil Biology

4.2 The Mucosal Barrier

4.3 Defence Against Microbes — Layers of Immune Defence

5. Aetiology

5.1 Bacterial Pathogens (Most Common Cause)

Gram-Positive Organisms (Now More Common)

Gram-Negative Bacilli (Traditionally Most Common; Most Dangerous)

5.2 Fungal Pathogens

5.3 Viral Pathogens

5.4 Other Pathogens

5.5 Common Sources of Infection

6. Pathophysiology

6.1 The Pathophysiological Cascade

6.2 Why Fever May Be the Only Sign

7. Classification

7.1 By Risk Category (IDSA / MASCC)

7.2 By Microbiological Documentation

8. Clinical Features

8.1 Symptoms

8.2 Signs

8.3 Special Clinical Scenarios

Neutropenic Enterocolitis (Typhlitis)

Ecthyma Gangrenosum

9. Approach to the Neutropenic Fever Patient — Pre-Diagnostic Framework

10. Summary of Key Pathophysiological Principles

Active Recall - Neutropenic Fever (Definition, Epidemiology, Aetiology, Pathophysiology, Clinical Features)

References

Framing the Problem

Approach to Differential Diagnosis — Overview Diagram

I. Infectious Causes (The Primary Concern)

A. Bacterial Infections

1. Gram-Positive Organisms

2. Gram-Negative Organisms

3. Anaerobic Bacteria

4. Other Bacteria

B. Fungal Infections

C. Viral Infections

D. Other Infectious Causes

II. Non-Infectious Causes of Fever in Neutropenic Patients

A. Drug Fever

B. Tumour Fever (Neoplastic Fever)

C. Transfusion Reactions

D. Graft-versus-Host Disease (GVHD)

E. Venous Thromboembolism (DVT / PE)

F. Adrenal Insufficiency

G. Other Non-Infectious Causes

III. Differential Diagnosis by Clinical Site

IV. Temporal Framework for Differential Diagnosis

V. Key Distinguishing Features — Infection vs. Non-Infectious Fever

VI. Summary Table of Differential Diagnosis

Active Recall - Differential Diagnosis of Neutropenic Fever

I. Diagnostic Criteria

The IDSA (Infectious Diseases Society of America) Diagnostic Criteria

Grading Severity for Risk Stratification

II. Diagnostic Algorithm

III. Investigation Modalities

A. Blood Investigations

1. Complete Blood Picture with Differential Count (CBP d/c)

2. Liver and Renal Function Tests (LRFT)

3. Electrolytes and Metabolic Panel

4. Inflammatory Markers

5. Coagulation Profile

6. Arterial Blood Gas (ABG)

B. Microbiological Investigations (The Centrepiece)

1. Blood Cultures — THE Most Important Investigation

2. Other Cultures (Directed by Clinical Findings)

3. Serological and Molecular Tests for Specific Pathogens

C. Imaging Investigations

1. Chest X-Ray (CXR)

2. CT Thorax (High Resolution)

3. CT Abdomen

4. CT Sinuses