GC102 Fever After Chemotherapy Infections In Immunocompromised Hosts
Febrile neutropenia and opportunistic infections occurring in immunocompromised patients following chemotherapy, requiring urgent evaluation and empiric broad-spectrum antimicrobial therapy due to impaired host defenses.
Fever After Chemotherapy: Infections in Immunocompromised Hosts
This lecture centres on a single critical clinical scenario: a patient who develops fever during the neutropenic nadir following chemotherapy. From this anchor case, the lecture systematically expands outward to cover the entire landscape of infections in immunocompromised hosts — not just neutropenia, but every major immune defect (cellular, humoral, barrier, device-related, splenectomy, biologics) and the specific pathogen spectrum each defect predicts.
Why this matters: Febrile neutropenia is a medical emergency. Untreated, it progresses to septic shock and death within hours because neutropenic patients cannot mount an adequate inflammatory response. You must start empirical broad-spectrum antibiotics before culture results. The lecture teaches you to: (1) recognize the immune defect, (2) predict the pathogen, (3) investigate efficiently, (4) treat empirically, and (5) prevent infections proactively.
How it fits in exams: This topic is extremely high-yield. Past papers repeatedly test: definitions (ANC thresholds), pathogen prediction by immune defect, empirical management of febrile neutropenia, temporal timeline of infections post-HSCT, and prevention strategies. It connects to GC 096 (Why do I always get sick), GC 100 (Defence against microbes), GC 048 (Fever), GC 060 (High WCC), and the haematology/oncology clinical blocks.
Core Definitions
Definition: oral temperature > 37.6°C more than once within a day; or single oral temperature > 38.3°C; or sustained ≥ 38.0°C for > 1 hour [1]
Why these thresholds? Fever is generated by pro-inflammatory cytokines (IL-1, TNF, IL-4, IL-6) released by endothelial cells and macrophages acting on the hypothalamic thermoregulatory centre. In an immunosuppressed host, the febrile response is the body's alarm system — and it is often the only sign of infection.
Fever may be blunted by steroids, chemotherapy, and NSAIDs [1]
This is a crucial clinical trap: a patient on dexamethasone for brain metastases or on high-dose steroids post-transplant can have raging sepsis with only a low-grade temperature or even be normothermic. Never be reassured by the absence of high fever in an immunocompromised patient.
Absolute Neutrophil Count (ANC) thresholds: [1]
- ANC < 1.5 × 10⁹/L → Neutropenia
- ANC < 0.5 × 10⁹/L → Severe neutropenia
- ANC < 0.1 × 10⁹/L → Profound neutropenia
Neutropenic fever is defined as ANC ≤ 0.5 × 10⁹/L (or ANC ≤ 1.0 expected to decline to ≤ 0.5 within 48h) PLUS single oral temperature ≥ 38.3°C OR sustained ≥ 38.0°C for > 1 hour [1][2]
Why ANC 0.5? This is the threshold below which the risk of clinically significant infection rises sharply. At ANC < 0.1, most bacteraemia episodes occur. The relationship is inversely proportional — the lower the ANC and the longer the duration of neutropenia, the higher the infection risk.
Post-chemotherapy neutropenia nadir: 7–14 days; duration: 14–28 days. 100% of patients will develop fever if neutropenic for ≥ 3 weeks. [1]
High Yield – Past Paper Direct Hit
2024 4th Summative MCQ Q84 asked: "For fever after chemotherapy, the risk of infection or bacteraemia is MOST RELATED to…?" Answer: The degree and duration of neutropenia [4]. Although mucositis and Hickman catheters contribute, the lecture explicitly frames severity and duration of neutropenia as the primary determinant.
M/25, AML-M2. Induction chemotherapy (Ara-C + daunorubicin). Day 7: 37.4°C, nausea, WBC 1.3, ANC 0.7. Day 10: sudden rigor, 39.2°C, sore throat/mouth, retrosternal pain on swallowing, watery diarrhoea 4×/day. P/E: diffuse oral erythema & ulcerations. Hb 7.2, WBC 0.1, Plt 30. [1]
Unpacking the case:
- By Day 10, ANC has crashed from 0.7 to effectively 0.1 (total WBC 0.1) = profound neutropenia at the expected nadir
- Rigor + 39.2°C = significant bacteraemia until proven otherwise
- Oral erythema/ulceration = chemotherapy-induced mucositis → the broken mucosal barrier allows translocation of oral/GI flora into the bloodstream
- Retrosternal pain on swallowing = likely oesophageal mucositis ± Candida oesophagitis or HSV oesophagitis
- Watery diarrhoea = GI mucosal damage ± C. difficile ± viral enteritis
- Hb 7.2, Plt 30 = pancytopenia from marrow aplasia post-chemotherapy (Plt < 50 → bleeding risk, also Plt dysfunction impairs immune defence)
This case perfectly illustrates the convergence of multiple risk factors: neutropenia + mucositis + indwelling catheter (likely Hickman) + thrombocytopenia.
An individual with alterations in innate & adaptive immunity as a result of underlying diseases & their therapy, which predispose the host to infections and/or neoplasia [1]
The Virulence–Immunity Spectrum
Outcome of infection determined by interplay between microbial virulence and host immunocompetence [1]
| Organism | Virulence | Causes Disease in Normal Host? | Significance in Immunocompromised |
|---|---|---|---|
| Rabies virus, Bacillus anthracis | Very high | Yes — always | Still pathogenic, same or worse |
| Dimorphic fungi (Histoplasma, etc.) | Moderate | Sometimes (geography-dependent) | Much more likely to cause disseminated disease |
| CMV, Candida albicans, Bacillus cereus | Low | Rarely (self-limiting or commensal) | Can cause life-threatening invasive disease |
Key principle: In the immunocompromised host, organisms that would normally be harmless commensals or environmental contaminants become lethal pathogens. This is why you must think of a completely different pathogen list.
Classification [1]:
- HIV vs Non-HIV
- Transplantation vs Non-transplantation
- BMT vs Solid organ (heart/lungs, liver, kidneys)
- Malignancy vs Non-malignancy
- Haematological vs Solid tumour
- Autoimmune disease
- Chronic diseases
- Splenectomy
- Congenital immunodeficiency
Why this classification matters: Different categories have different dominant immune defects. A patient with CLL has humoral immune dysfunction. A patient post-allogeneic HSCT has neutropenia early, then cellular immune dysfunction late. An HIV patient with CD4 < 50 has severe T-cell depletion. Each predicts a different pathogen profile.
| # | Mechanism | Examples | Pathogen Implications |
|---|---|---|---|
| 1 | Granulocytopenia (Neutropenia) | Chemo, AML, aplastic anaemia, BMT | Bacteria (GNR, GPC), Candida, Aspergillus |
| 2 | Cellular immune dysfunction (T lymphocytes) | HIV/AIDS, post-transplant IS, lymphoma | Intracellular bacteria, fungi, viruses, protozoa, helminths |
| 3 | Humoral immune dysfunction (B lymphocytes/Antibody) | CLL, myeloma, post-splenectomy, CVID | Encapsulated bacteria |
| 4 | Skin/mucosal barrier damage | Burns, chemo/RT mucositis | Skin and gut flora translocation |
| 5 | Medical/surgical procedures, indwelling devices, antimicrobial therapy | Hickman catheter, urinary catheter, broad-spectrum antibiotics | Catheter-related BSI, resistant organisms, C. difficile |
| 6 | Major organ dysfunction | Tumour obstruction, neurological dysfunction (loss of gag reflex → aspiration), splenectomy, cirrhosis, uraemia, heart failure, COPD, gastric hypochlorhydria | Site-specific infections |
| 7 | Miscellaneous | Thrombocytopenia, complement deficiency, iron overload, malnutrition ( < 75% IBW), autoantibodies vs cytokines (e.g. anti-IFN-γ) | Variable |
| 8 | Biologics | MnAb vs TNF, IL-2, IL-6R, IL-12, IL-23; JAK/STAT kinase inhibitors | TB reactivation (anti-TNF), opportunistic infections |
Why Biologics Matter – Exam Trend
The lecture specifically highlights monoclonal antibodies against cytokines/receptors (e.g. anti-TNF, anti-IL-2, anti-IL-6R, anti-IL-12, anti-IL-23) and JAK/STAT kinase inhibitors as modern causes of immunosuppression [1]. Anti-TNF agents (infliximab, adalimumab) are notorious for reactivating latent TB — this is a classic exam question. JAK inhibitors (tofacitinib, baricitinib) disrupt multiple cytokine signalling pathways and predispose to herpes zoster reactivation, opportunistic infections, and TB.
Spectrum of Pathogens by Specific Immune Defect
This is the conceptual backbone of the entire lecture: know the defect → predict the pathogen.
1. Neutropenia
Pathogens in neutropenia [1]:
| Category | Organisms | Source |
|---|---|---|
| Gram-negative rods (gut) | Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa | GI translocation through damaged mucosa |
| Gram-positive cocci (skin) | Staphylococcus epidermidis, Staphylococcus aureus, Viridans streptococci (S. mitis), Enterococcus spp. | Skin flora, catheter, oral mucosa |
| Yeasts | Candida spp., Trichosporon spp. | GI/GU mucosal translocation |
| Moulds | Aspergillus, Mucoraceae, Fusarium spp. | Air spores (inhalation) |
The temporal progression is critical:
- Bacteria appear first (within days of neutropenia onset)
- Yeasts (Candida) appear next (after ~1 week of persistent neutropenia, especially with broad-spectrum antibiotics)
- Moulds (Aspergillus) appear last (after ~2 weeks of prolonged neutropenia)
The severity and duration of neutropenia determine the pathogen spectrum [1]
Why this sequence? Bacteria are fast-growing and exploit mucosal breaches immediately. Yeasts like Candida are slower-growing but become dominant when antibacterial agents suppress bacterial competition. Moulds like Aspergillus require prolonged immune failure to germinate from inhaled spores and invade tissue.
Chemotherapy-induced mucositis causes damage to mucosa throughout the alimentary system. The endogenous bacterial/fungal flora seeds the bloodstream and causes the majority of neutropenic fever cases. [2]
The lecture slides show a model with three key anatomical junctions where microbial translocation occurs:
- CPJ (Cardiopharyngeal junction / throat)
- GEJ (Gastroesophageal junction)
- ICJ (Ileocaecal junction)
These are sites of high microbial biomass where chemotherapy-damaged mucosa allows organisms to cross into the bloodstream. The skin (especially around Hickman catheter sites) and the respiratory tract (inhalation of airborne mould spores) are the other major portals of entry.
Bacterial biofilm on intravascular catheters leads to persistence [1]
This explains why catheter-related bloodstream infections (CRBSI) are so difficult to eradicate — the biofilm protects organisms from antibiotics and immune cells. Removal of the catheter is often necessary.
In 968 episodes of fever and neutropenia (Ann Intern Med 1994) [1]:
- Microbiologically documented infection: ~30%
- Clinically documented infection (clinical focus but no organism): ~20-30%
- Fever of unknown origin / unexplained fever: ~40-50%
This is a landmark statistic: in the majority of febrile neutropenic episodes, no pathogen is ever identified. That is precisely why empirical therapy is mandatory — you cannot afford to wait for cultures because most will be negative, and the patient may die waiting.
Pathogens in cellular immune dysfunction [1]:
| Category | Organisms | Key Features |
|---|---|---|
| Bacteria | Listeria, Salmonella, Legionella, Mycobacteria (TB & NTM), Nocardia | Usually intracellular pathogens of the RES |
| Fungi | Cryptococcus neoformans, Dimorphic fungi, Pneumocystis jirovecii, Microsporidia | PCP is the hallmark AIDS-defining illness |
| Viruses | VZV, CMV, HSV, EBV, HHV-6, Respiratory viruses, HPV | Reactivation of latent herpesviruses |
| Protozoa | Toxoplasma, Cryptosporidium | Toxoplasma brain abscess in AIDS |
| Helminths | Strongyloides stercoralis | Hyperinfection syndrome |
Why intracellular pathogens? T-helper cells (CD4+) are essential for activating macrophages to kill intracellular organisms. Without functional CD4+ T cells, organisms that hide inside macrophages (Listeria, Salmonella, Mycobacteria) or inside other cells (CMV, Toxoplasma) replicate unchecked.
Classic clinical context: HIV with CD4 < 200 → PCP; CD4 < 100 → Toxoplasma brain abscess, Cryptosporidium; CD4 < 50 → CMV retinitis, disseminated MAC, disseminated Talaromyces (Penicillium) marneffei [1][5].
Pathogens in humoral immune dysfunction and post-splenectomy [1]:
| Category | Organisms | Mechanism |
|---|---|---|
| Encapsulated bacteria | Streptococcus pneumoniae, Haemophilus influenzae, Capnocytophaga canimorsus | Need antibody + complement for opsonization; spleen provides IgM, tuftsin, properdin, and filters poorly opsonized organisms |
| Protozoa | Babesia microti | Intra-erythrocytic parasite filtered by spleen |
| Others | Salmonella, Neisseria, Plasmodium | Also require splenic clearance |
Why encapsulated bacteria? Their polysaccharide capsules resist phagocytosis unless opsonized by specific antibodies (IgG, IgM) and complement. Without B-cell function (e.g. CLL, CVID, myeloma) or without a spleen (which is the major site of IgM production and filtration of poorly opsonized organisms), these bacteria cause overwhelming post-splenectomy infection (OPSI) — fulminant sepsis with DIC, purpura fulminans, and death within 24 hours.
High Yield – Past Paper: 2021 SAQ Q12c
The scenario of a patient 4 years post-BMT who did not return for routine vaccination, presenting with sudden high fever, hypotension, purpuric rash, and death within 24 hours (with Howell-Jolly bodies on blood film indicating functional asplenia) asks for 3 organisms: S. pneumoniae, H. influenzae, N. meningitidis (encapsulated bacteria causing OPSI) [6].
Temporal Relationship of Infections Post-HSCT
This is one of the most commonly tested frameworks from this lecture.
Timeline of opportunistic infections after haematopoietic stem cell transplant [1]:
- Dominant defect: Neutropenia + mucosal barrier damage (from conditioning chemotherapy ± TBI)
- Risk factors: Cytotoxic conditioning, TBI, blood products, Hickman catheter
- Pathogens:
- Bacteria (gut/oral/skin flora): E. coli, Klebsiella, Pseudomonas, Staph, Strep
- HSV-1 & HSV-2 reactivation (Day 0–14) — from orolabial/genital latent infection
- HHV-6 & HHV-7 (Day 20–27)
- Candida → Moulds (Aspergillus) as duration increases
- Dominant defect: Cellular immune dysfunction from acute GVHD and its treatment (intense immunosuppression with steroids and other agents)
- Pathogens:
- CMV (classically Day 36 — the most important virus in this phase), Adenovirus, BK virus, JC virus
- EBV-related PTLD (post-transplant lymphoproliferative disorder)
- Aspergillus + PCP (if prophylaxis not taken)
- Reactivation of HBV, HCV, HEV, VZV
- Children: RSV, parainfluenza (for shedders)
- Dominant defect: Chronic GVHD (if immunosuppression not tapered) → functional asplenia + ongoing cellular immune dysfunction
- Pathogens:
- Encapsulated bacteria (S. pneumoniae, H. influenzae) — especially if no revaccination
- Late CMV disease with antiviral resistance
- VZV reactivation
High Yield – Past Paper: 2021 SAQ Q12
Part (a): Day 10 post-conditioning, ANC < 0.1 — name common blood culture organisms → GNR (E. coli, Klebsiella, Pseudomonas) + GPC (S. epidermidis, Viridans streptococci) [6]
Part (b): Day 28 post-engraftment, fever + impaired LFT + diarrhoea + CXR infiltrates, didn't take prophylaxis → CMV (hepatitis + colitis + pneumonitis), PCP (CXR infiltrates), Aspergillus (lung infiltrates) [6]
Part (c): 4 years post-transplant, fulminant sepsis with purpura, Howell-Jolly bodies → S. pneumoniae, H. influenzae, N. meningitidis (OPSI) [6]
2022 4th Summative MCQ Q19-21 [7]:
- Q19: HIV, CD4 60, disseminated skin papules, bilateral infiltrates, hepatosplenomegaly → Talaromyces marneffei (dimorphic fungus, endemic in SE Asia, CD4 < 100)
- Q20: AML, severe prolonged neutropenia, on meropenem, breakthrough fever + worsening oral mucositis, blood culture positive → Streptococcus mitis (Viridans streptococcus — breakthrough bacteraemia during meropenem, associated with severe mucositis)
- Q21: Post-liver transplant, on prednisolone + tacrolimus + MMF, low-grade fever + diarrhoea + abdominal pain, endoscopic biopsy shows inclusion bodies → CMV (CMV colitis with characteristic "owl's eye" inclusion bodies)
Exam Trap – S. mitis vs E. coli
When a neutropenic patient on broad-spectrum antibiotics (especially meropenem which covers GNR) develops breakthrough fever with oral mucositis, think Viridans streptococci (S. mitis) — these are part of the oral flora and are NOT well covered by carbapenems. This is a classic exam discriminator [7].
Special features of infection in immunocompromised hosts [1]:
| Feature | Explanation |
|---|---|
| 1. Spectrum predicted by specific defect | Know the defect → know the pathogen |
| 2. Unusual pathogens | (a) Environmental organisms or normal commensals become pathogenic; (b) Reactivation of latent organisms (old TB foci, herpesviruses) |
| 3. Rapid clinical deterioration | Without adequate immune response, infection spreads unchecked → fulminant sepsis |
| 4. Subtle clinical presentation | Minimal inflammation → no pus, no consolidation on CXR, no meningism despite meningitis → fever may be the ONLY sign |
| 5. Multiple organisms | Co-infection is common (e.g. bacterial + fungal, CMV + PCP) |
| 6. Virus-associated cancers | Prolonged immunosuppression → oncogenic virus-driven neoplasia: EBV-related PTLD, HHV-8 Kaposi's sarcoma, HPV-related anogenital cancers |
Why subtle presentation? Pus formation requires neutrophil accumulation. Without neutrophils, an abscess cannot form, a pneumonia cannot consolidate, and meningitis may not cause CSF pleocytosis. This is why you must have a high index of suspicion and investigate aggressively even with minimal symptoms.
Clinical Approach to Neutropenic Fever
Full Hx & P/E (daily): [1]
- Skin (including catheter exit sites, bone marrow biopsy sites)
- Oral cavity (mucositis, oral candidiasis, HSV ulcers)
- Lungs (subtle crackles, even normal examination doesn't exclude pneumonia)
- Abdomen (tenderness — may indicate typhlitis/neutropenic enterocolitis)
- Perianal area (abscess — DO NOT do digital rectal examination in neutropenic patients as this can cause bacteraemia)
- Hickman catheter exit site (erythema, discharge, tunnel tenderness)
- Bone marrow biopsy site
- Over nasal sinuses (sinusitis — especially Aspergillus)
Approach to investigation of neutropenic fever [1]:
| Investigation | Indication | What You're Looking For |
|---|---|---|
| CBP, LFT, RFT | All patients | Baseline; trends in counts; organ dysfunction |
| Blood cultures | All patients — from central venous catheter through 2 different ports (+ peripheral venipuncture if infected catheter suspected) | Identify causative organism; differential time to positivity helps diagnose CRBSI |
| CXR | Low-risk patients; CT lung for high-risk or symptomatic | Infiltrates, nodules (may be absent due to neutropenia) |
| CT chest | High-risk or symptomatic (cough, SOB, pleuritic pain) | Halo sign (ground-glass halo around a nodule = angioinvasive aspergillosis) |
| CT abdomen | Abdominal pain, tenderness, diarrhoea | Typhlitis (caecal wall thickening), hepatosplenic candidiasis |
| Stool for C. difficile | Diarrhoea | C. difficile cytotoxin and culture |
| Urine, skin swab, sputum | If symptoms or clinical/radiological lesions present | Culture + sensitivity |
| BAL (bronchoalveolar lavage) | Pulmonary infiltrates not responding to empirical therapy | PCP, Aspergillus, CMV, other fungi |
| Serial serum galactomannan | High-risk patients / suspected invasive aspergillosis | Galactomannan is a cell wall component of Aspergillus — serum levels rise during invasive disease |
| 1,3 β-D-glucan | Broad fungal screening | β-D-glucan is a cell wall component common to most pathogenic fungi (not Mucor/Crypto) |
Why Blood Cultures From 2 Ports?
Drawing blood cultures from two different lumens of a multi-lumen central venous catheter (or one central + one peripheral) serves two purposes: (1) increases sensitivity of detection; (2) allows differential time to positivity (DTP) — if the central line culture becomes positive ≥ 2 hours before the peripheral culture, this suggests the catheter is the source (catheter-related bloodstream infection, CRBSI).
6-Step Management Framework (RECOGNITION to MONITORING)
The lecture presents a 6-step management framework [1]:
| Step | Action | Details |
|---|---|---|
| 1. RECOGNITION | Identify the specific immune defect | Neutropenia? T-cell dysfunction? Humoral? Barrier? |
| 2. SUSPICION | Maintain high suspicion for infection from minimal symptoms | Low-grade fever, mental dullness may be the ONLY signs |
| 3. TAKING | Collect appropriate clinical specimens | Blood cultures, BAL, etc. for direct microscopy, antigen detection, culture |
| 4. COOPERATION | Collaborate with clinical microbiologist | Request unusual pathogens (PCP, fungi, Nocardia) — don't just request "routine culture" |
| 5. THERAPY | (a) Early aggressive empirical antimicrobial therapy BEFORE definitive culture results; (b) Temporary replacement: buffy coat (neutrophil) transfusion; (c) Ex-vivo expanded T lymphocytes: adoptive transfer of virus-specific immunity vs EBV, CMV, or adenovirus | This is a MEDICAL EMERGENCY |
| 6. MONITORING | Monitor for efficacy and side effects | Drug assays (e.g. vancomycin levels, voriconazole levels) |
The handout specifically mentions intravenous imipenem as an example of empirical therapy in febrile neutropenia [2]. In current practice, any antipseudomonal beta-lactam (piperacillin-tazobactam, cefepime, meropenem, or imipenem) is acceptable as first-line monotherapy.
Why antipseudomonal coverage? Pseudomonas aeruginosa bacteraemia in a neutropenic patient carries extremely high mortality if not covered from the start. Even though GPC (S. epidermidis) are now the most commonly isolated organisms, Pseudomonas remains the most dangerous, so empirical regimens must cover it.
When to add vancomycin: Suspected catheter-related infection, severe mucositis (Viridans streptococci), skin/soft tissue infection, known MRSA colonization, hemodynamic instability.
When to add antifungals: Persistent fever after 4-7 days of broad-spectrum antibiotics despite neutropenia → escalate to empirical antifungal therapy (e.g. caspofungin, liposomal amphotericin B, or voriconazole).
Buffy coat (neutrophil) transfusion: for bacterial infection not responding to antibiotics in patients with persistent neutropenia [2]
Adoptive transfer of ex-vivo expanded virus-specific T lymphocytes: for drug-resistant CMV, disseminated adenovirus, EBV-related PTLD [1][2]
Paradoxical deterioration: Immune Reconstitution Inflammatory Syndrome (IRIS) — can occur with recovery of CD4 count after antiretroviral therapy; or Myeloid Reconstitution Syndrome — can occur with ANC recovery after chemotherapy [2]
Why IRIS? When the immune system recovers (e.g. after starting ART or after neutrophil engraftment post-HSCT), it can mount an exuberant inflammatory response against previously subclinical infections, causing paradoxical worsening (new fever, new inflammatory foci, progression of existing lesions). This is not treatment failure — it is a sign of immune recovery, but it can be life-threatening.
| Strategy | Details | Why |
|---|---|---|
| 1. Avoid unnecessary invasive procedures or antimicrobials | Don't disturb the ecological balance of microbial flora | Broad-spectrum antibiotics → C. difficile, resistant organisms, fungal overgrowth |
| 2. Treat established foci BEFORE immunosuppression | Carious teeth, chronic sinusitis, asymptomatic bacteriuria, anal fissures, recurrent boils, ingrown toenails, chronic Salmonella carriage | These become sources of life-threatening infection once immune defences are suppressed |
| 3a. Protective isolation + low-microbe food | HEPA-filtered rooms for HSCT patients | Prevents inhalation of Aspergillus spores |
| 3b. Prophylactic antibiotics | Fluoroquinolone prophylaxis in high-risk neutropenia (varies by institution) | Reduces GNR bacteraemia |
| 3c. Prophylactic antivirals | Acyclovir (HSV/VZV), Ganciclovir (CMV), Entecavir (HBV) | Prevents reactivation of latent viruses |
| 3d. Prophylactic antifungals | Fluconazole (Candida), Voriconazole/Posaconazole (yeasts + moulds), Septrin/Co-trimoxazole (PCP/Pneumocystis jirovecii) | PCP prophylaxis is critically important in T-cell dysfunction |
| 3e. Prophylactic antiparasitic | Septrin (Toxoplasma gondii) | Septrin does double duty: PCP + Toxoplasma |
| 3f. Active immunisation | Post-transplant revaccination schedule | Immune memory lost after HSCT; revaccination prevents late infections |
| 3g. Passive immunisation | IVIG (intravenous immunoglobulin) | Replaces deficient antibodies in hypogammaglobulinaemia |
| 3h. Acceleration of immune recovery | G-CSF (granulocyte colony-stimulating factor) | Shortens duration of neutropenia → reduces infection risk |
| 3i. Adoptive T-cell transfer | Ex-vivo expanded virus-specific T lymphocytes | Prevention of PTLD, CMV, adenovirus in high-risk transplant recipients |
Septrin Does Triple Duty
Co-trimoxazole (Septrin) is used for prophylaxis against: (1) Pneumocystis jirovecii, (2) Toxoplasma gondii, and (3) has some activity against Nocardia. It is one of the most important prophylactic agents in immunocompromised patients [1].
The lecture shows CT images at Day 10 and Day 13 [1] demonstrating pulmonary infiltrates consistent with invasive fungal infection (likely invasive pulmonary aspergillosis). The halo sign on CT (ground-glass opacity surrounding a pulmonary nodule) is the classic early finding of angioinvasive aspergillosis — it represents haemorrhage around the fungal nodule due to vascular invasion.
Culture of Aspergillus fumigatus [1] — the lecture shows the classic appearance of A. fumigatus on culture with characteristic conidiophores.
Clinical correlation: In a profoundly neutropenic patient with persistent fever despite broad-spectrum antibiotics, new pulmonary nodules on CT with a halo sign + positive serum galactomannan → diagnose invasive pulmonary aspergillosis and start voriconazole (drug of choice).
Low CD4 lymphocyte count < 50/mm³ in HIV [1]
The lecture slide references the correlation between CD4 count and opportunistic infections:
| CD4 Count | Opportunistic Infections |
|---|---|
| < 500 | Candidal vaginitis, Kaposi sarcoma, TB |
| < 200 | PCP, Toxoplasmosis (cerebral), Cryptococcosis |
| < 100 | Disseminated MAC, CMV retinitis |
| < 50 | Disseminated Talaromyces marneffei (SE Asia), progressive multifocal leukoencephalopathy (JC virus) |
Monoclonal antibodies (MnAbs) against interconnecting cytokine/chemokine & receptors [1]
The lecture specifically highlights that modern biological therapies used in autoimmune diseases, inflammatory conditions, and transplant medicine create new patterns of immunosuppression:
- Anti-TNF (infliximab, adalimumab, etanercept) → TB reactivation, invasive fungal infections, Listeria
- Anti-IL-6R (tocilizumab) → blunts fever response (masks infections!), TB
- Anti-IL-12/IL-23 (ustekinumab) → mycobacterial infections
- Anti-CD20 (rituximab) → B-cell depletion → hypogammaglobulinaemia → progressive multifocal leukoencephalopathy
JAK-STAT kinase inhibitors [1] (tofacitinib, baricitinib, ruxolitinib) → disrupt signalling of multiple cytokines simultaneously → increased risk of herpes zoster, opportunistic infections, TB
| Related Lecture | Connection |
|---|---|
| GC 048 (Fever) | General fever definitions and mechanisms; this lecture applies them to the immunocompromised setting |
| GC 060 (High WCC) | AML diagnosis, chemotherapy complications, neutropenic fever as a haematological emergency |
| GC 096 (Why do I always get sick) | Primary immunodeficiencies — congenital counterpart to acquired immunodeficiency |
| GC 100 (Defence against microbes) | Innate and adaptive immunity basics that underpin understanding of each immune defect |
| GC 101 (Diagnosis of infections) | How to investigate infections (cultures, serology, molecular); applies directly to specimens in febrile neutropenia |
| GC 106 (Practical issues in antibiotic use) | Empirical vs targeted therapy, de-escalation, drug levels |
| GC 144 (Recurrent infections in children) | Primary immunodeficiencies — overlap with phagocytic defects (CGD), complement deficiency |
Likely Exam Questions
-
A 35-year-old man with AML is Day 12 post-induction chemotherapy. He develops fever 39°C. ANC is 0.08 × 10⁹/L. Describe your approach to management. [Expected: definition of neutropenic fever; septic workup (blood cultures from 2 ports, CBP, LFT, RFT, CXR); empirical antipseudomonal antibiotics within 1 hour; daily examination of skin, oral cavity, perianal, catheter site, lungs, abdomen; consider antifungal escalation if fever persists]
-
List the common pathogens causing neutropenic fever at Day 10 post-chemotherapy. [Expected: GNR — E. coli, Klebsiella, Pseudomonas; GPC — S. epidermidis, S. aureus, Viridans streptococci (S. mitis), Enterococcus; Yeasts — Candida spp.]
-
For each immune defect, list 3 predicted pathogens: (a) Neutropenia, (b) T-cell dysfunction, (c) Humoral/post-splenectomy. [Expected: as per tables above]
-
A patient is Day 28 post-HSCT, not compliant with prophylaxis, with fever + CXR infiltrates + diarrhoea + deranged LFT. What organisms might account for this? [Expected: CMV, PCP, Aspergillus]
-
List 4 preventive measures against infection in immunocompromised hosts. [Expected: protective isolation/HEPA, prophylactic antivirals, prophylactic antifungals/Septrin, active immunisation, G-CSF, avoid unnecessary invasive procedures]
-
Which factor is MOST related to the risk of bacteraemia in febrile neutropenia? → Degree and duration of neutropenia [4]
-
A neutropenic patient on meropenem develops breakthrough fever and worsening oral mucositis. The most likely organism in blood culture is? → Streptococcus mitis (Viridans streptococcus) [7]
-
Which investigation is most useful for diagnosing invasive aspergillosis? → Serial serum galactomannan + CT chest (halo sign)
High Yield Summary
Neutropenic fever = ANC ≤ 0.5 + fever ≥ 38.3°C (single) or ≥ 38.0°C sustained > 1h → MEDICAL EMERGENCY → empirical antipseudomonal antibiotics WITHIN 1 HOUR.
Know the immune defect → predict the pathogen:
- Neutropenia → bacteria (GNR/GPC), then Candida, then Aspergillus (temporal sequence)
- T-cell dysfunction → intracellular bacteria, PCP, CMV, Toxoplasma, Strongyloides
- Humoral/Splenectomy → encapsulated bacteria (S. pneumoniae, H. influenzae, N. meningitidis)
Post-HSCT timeline: Phase 1 (0-30d) = bacteria + HSV + Candida/Aspergillus; Phase 2 (30-120d) = CMV + PTLD + PCP; Phase 3 ( > 120d) = encapsulated bacteria + late CMV.
Prevention: avoid unnecessary procedures, treat foci before immunosuppression, HEPA rooms, prophylactic acyclovir/fluconazole/Septrin, G-CSF, revaccination.
Biologics (anti-TNF, JAK inhibitors) create new patterns of immunosuppression — screen for latent TB before starting.
Fever may be blunted by steroids/chemo/NSAIDs — maintain HIGH index of suspicion.
Active Recall - Fever After Chemotherapy & Infections in Immunocompromised Hosts
[1] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts.pdf [2] Lecture slides: GC 102. Fever after chemotherapy infections in immunocompromised hosts [Handout].pdf [3] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1329-1332) [4] Past papers: 2024 Fourth Summative MCQ.pdf (Q84) [5] Senior notes: Block A - HIV positive_ HIV related diseases, accidental needle prick injury.pdf [6] Past papers: 2021 Fourth Summative SAQ.pdf (Q12) [7] Past papers: 2022 Fourth Summative MCQ.pdf (Q19-21) [8] Senior notes: Adrian Lui Pediatrics Notes.pdf (p423) [9] Senior notes: Ryan Ho Haemtology.pdf (p70) [10] Past papers: 2020 Fourth Summative Assessment MCQ paper.pdf (Q82)
GC101 Diagnosis Of Infections
Diagnosis of infections is the systematic process of identifying causative pathogens through clinical assessment, microbiological techniques (culture, microscopy, serology, molecular methods), and laboratory markers to guide appropriate antimicrobial therapy.
GC103 Fever After Travelling
Fever occurring in a patient who has recently traveled, particularly to tropical or endemic regions, requiring systematic evaluation for infections such as malaria, dengue, typhoid, and other travel-related diseases.