• M/35, chronic smoker, good past health
• URTI symptoms (sore throat, running nose) 10 days ago ← the preceding viral illness
• Increasing cough and greenish sputum over past 5 days
• Progressive SOB with right pleuritic chest pain for 3 days
• High swinging fever with chills and rigor for 3 days
• Seen by GP → oral antibiotics + paracetamol → worsening → A&E

• Respiratory distress, mentally alert
• Chest: dullness, bronchial breath sound, and coarse inspiratory crackles over right lower chest
• BP 90/50 mmHg (hypotension → septic shock territory)
• SpO₂ 92% on room air (hypoxaemia)

Why this is CAP and not something else:

• Onset in the community (not hospitalised)
• Preceded by URTI → secondary bacterial infection is classic
• Consolidation signs (dullness + bronchial breath sounds + crackles) = lobar consolidation
• Systemic toxicity (high swinging fever, chills, rigor)

Why is he sick?

• Hypotension (BP 90/50) suggests sepsis/septic shock
• Hypoxaemia (SpO₂ 92%) suggests significant parenchymal involvement
• These features push him into the "severe CAP" category

Inflammation of lung parenchyma, commonly due to infective agents (bacteria, viruses or fungi). ^[1]

This is important: pneumonia = parenchymal inflammation. Bronchitis = airway inflammation. That's why you see consolidation on CXR in pneumonia but not in bronchitis.

Pneumonia: 2nd leading cause of death in HK since 2012; 17% of deaths in 2022; 42,403 hospital admissions (2.34% of total) in 2021.

This is HK-specific data the examiners love. Pneumonia overtook cancer as the 2nd leading cause of death in 2012 (it was 3rd from 2003-2011).

Cough, sputum, haemoptysis, dyspnoea, pleuritic chest pain; fever, chills, rigor; confusion, constitutional or systemic symptoms.

Why each symptom occurs:

• Cough + sputum: inflammatory exudate in alveoli stimulates cough reflex; purulent sputum = neutrophilic response to bacterial infection
• Haemoptysis: necrosis of alveolar tissue or inflamed bronchial mucosa
• Pleuritic chest pain: inflammation reaching the visceral/parietal pleura → sharp, stabbing pain worse with inspiration
• Fever/chills/rigor: systemic inflammatory response; rigor (uncontrollable shaking) suggests bacteraemia
• Confusion: especially in elderly; marker of severe disease (the "C" in CURB-65)

Chest: percussion dullness, bronchial breath sound, coarse crackles, increased vocal resonance. Vital signs: BP, SpO₂; mental state.

Why these signs occur — from first principles:

• Percussion dullness: consolidated (solid) lung transmits percussion energy poorly → dull note (vs resonant normal air-filled lung)
• Bronchial breath sounds: normally heard only over trachea. When lung is consolidated, it conducts sound from central airways to the chest wall without filtering → harsh, hollow quality heard peripherally
• Coarse crackles: secretions in airways "pop" open during inspiration
• Increased vocal resonance (including whispering pectoriloquy and aegophony): consolidated lung transmits voice sounds more efficiently than air-filled lung

Travel, Occupation, Contact, Clustering

This is crucial for identifying atypical pathogens and notifiable diseases:

• Travel: Legionella (contaminated water systems, hotels), TB (endemic areas), MERS (Middle East)
• Occupation: healthcare workers (TB, influenza), farmers (Q fever, melioidosis)
• Contact: household contacts with similar illness → viral, TB
• Clustering: outbreak → influenza, COVID-19, Legionella

Usually refers to M. pneumoniae, C. pneumoniae, L. pneumophila. Syndrome of pneumonitis, fever, and a relatively normal WBC, without identifiable bacterial pathogens. Prominent systemic complaints.

Why "atypical"?

• These organisms don't grow on standard blood agar/chocolate agar (hence "without identifiable bacterial pathogens")
• They cause interstitial rather than alveolar inflammation → less sputum production
• Systemic symptoms (headache, myalgia, malaise) are disproportionately prominent vs respiratory symptoms
• WBC is typically normal (unlike typical bacterial pneumonia where WBC is elevated)
• CXR often shows patchy/interstitial infiltrates rather than dense lobar consolidation

Compatible respiratory symptoms and signs + Chest X-ray: consolidations in lobar pneumonia; patchy infiltrates in bronchopneumonia.

CXR is the gold standard for diagnosis. You need BOTH clinical features AND radiographic evidence. A patient with cough and fever but a clear CXR does NOT have pneumonia (they have acute bronchitis or URTI).

Further investigations:

• Complete blood counts (total WBC and differential counts)
• Electrolytes, liver and renal function tests
• Arterial blood gases
• Atypical pneumonia serology
• Nasopharyngeal aspirate if influenza or atypical pneumonia suspected
• Urinary antigen test for Legionella and pneumococcus
• Sputum and blood cultures

Why each investigation matters:

Microbiological diagnosis is retrospective. Initial management is based on clinical setting and host factors.

This is a critical teaching point: you almost never know the pathogen when you start treatment. You must use clinical context to make your best guess and start empirical therapy.

Need to cover Streptococcus pneumoniae in ALL cases of CAP. Need to cover Legionella pneumophila in SEVERE cases of CAP.

Why cover Legionella in severe CAP?

• Legionella causes severe disease with multi-organ involvement
• It is an intracellular pathogen → beta-lactams alone won't work
• Requires macrolide (azithromycin/clarithromycin) or fluoroquinolone for coverage
• This is why severe CAP regimens always include a macrolide

CURB-65:

• C — Confusion
• U — Urea > 7 mmol/L
• R — Respiratory rate > 30/min
• B — Blood pressure (SBP < 90 mmHg OR DBP < 60 mmHg)
• 65 — Age > 65 ≥2 factors present → hospital admission

Apply to the case: The 35-year-old man has: BP 90/50 (✓B), SpO₂ 92% (implies RR likely elevated), no confusion mentioned. Score ≥2 → hospital admission. Given hypotension → consider ICU.

Poor prognostic factors: old age, hypoxaemia (PaO₂ < 8 kPa), high ( > 11 × 10⁹/L) or low WBC ( < 4 × 10⁹/L), high urea ( > 8 mmol/L), multilobar involvement, bacteraemia. ^[1]

Need to administer appropriate antibiotics timely (preferably within 6-8 hours).

Empirical regimen: Penicillin with beta-lactamase inhibitor +/- macrolide or tetracycline. E.g. Amoxicillin-clavulanate (Augmentin) +/- clarithromycin or azithromycin or doxycycline. Duration ~7-10 days.

Why this combination?

• Amoxicillin-clavulanate (Augmentin): covers S. pneumoniae, H. influenzae (including beta-lactamase producing strains), and many Gram-negatives. The clavulanate inhibits beta-lactamase enzymes that would otherwise destroy amoxicillin.
• Macrolide (clarithromycin/azithromycin) or doxycycline: covers atypical pathogens (Mycoplasma, Chlamydophila, Legionella) which are intracellular and not covered by beta-lactams. Added especially in severe CAP to cover Legionella.

Risk factors for multi-drug resistant pathogens: recent/frequent antibiotic use, recent/frequent hospitalization, nursing home residents, immunosuppressive disease or therapy. ^[1]

Why this matters: If MDR risk factors are present, you may need to escalate beyond standard Augmentin to broader-spectrum agents (e.g., respiratory fluoroquinolone or broader beta-lactam).

O₂ or mechanical ventilation for respiratory failure; chest physiotherapy; fluid rehydration; treat underlying COPD with bronchodilators; control cardiac arrhythmias (e.g. AF).

Why AF in pneumonia?

• Infection → systemic inflammation → autonomic imbalance + hypoxia + fever → triggers atrial fibrillation, especially in elderly patients
• AF with rapid ventricular response can worsen haemodynamic status
• Usually reverts with treatment of the underlying infection

Pneumonia occurring > 48 hours after hospitalization.

This time threshold is critical — it distinguishes HAP from CAP that was incubating at the time of admission.

Mostly related to aspiration of oropharyngeal secretions colonized by hospital-acquired organisms.

Why hospitals are different: The oropharynx becomes colonized with Gram-negative bacilli and resistant organisms within 48 hours of hospital admission (due to altered mucosal defences, exposure to antibiotics, supine positioning, and invasive devices).

General debility and old age, cigarette smoking, COPD, aspiration, post-GA, H₂ blockers or antacids, nasogastric tube, mechanical ventilation (VAP).

Why H₂ blockers/antacids? They raise gastric pH → allow bacterial colonization of the stomach → retrograde colonization of the oropharynx → aspiration. This is a classic exam question.

Cover Strep. pneumoniae, resistant Gram +ve (may include MRSA), Gram -ve (Klebsiella, Pseudomonas, ESBL-producing organisms), anaerobes. Extended spectrum penicillin or third-generation cephalosporin or carbapenem. E.g. piperacillin-tazobactam (Tazocin) or meropenem.

Why broader spectrum than CAP?

• HAP pathogens are more resistant (hospital environment selects for resistance)
• Must cover Pseudomonas (which is inherently resistant to many antibiotics)
• ESBL-producers are not covered by standard cephalosporins → need carbapenems
• May add vancomycin if MRSA is suspected

Altered consciousness, alcoholism, vomiting, dysphagia and oesophageal diseases, neurological disorders (bulbar palsy), nasogastric tube feeding, severe dental or URTI, terminal illness, drowning.

Common thread: All these conditions impair airway protective reflexes (gag, cough, swallowing coordination) → aspiration of oropharyngeal or gastric contents into the lower respiratory tract.

Usually affects dependent parts of lungs:

• Lower lobes (especially on the right)
• Posterior segments of upper lobes (in those mostly recumbent)

Why right lower lobe? The right main bronchus is wider, shorter, and more vertical than the left → aspirated material preferentially flows to the right lung.

Videofluoroscopic swallowing test (VFSS) — to confirm swallowing dysfunction and guide feeding strategy.

Antibiotics covering oropharyngeal flora especially anaerobes → Penicillins → e.g. amoxicillin-clavulanate (Augmentin). Treatment of underlying conditions. Prevention of further aspiration → non-oral feeding (e.g. via percutaneous endoscopic gastrostomy [PEG]).

• Severe pneumonia → widespread alveolar consolidation → V/Q mismatch → hypoxaemia
• May progress to ARDS if overwhelming inflammation

• Bacteraemia → sepsis → septic shock → organ dysfunction (renal, hepatic, coagulopathy)

Air-fluid level, cavity. Could be polymicrobial. Needs prolonged (4-6 weeks) antibiotics. No need for percutaneous drainage in most cases.

Why 4-6 weeks? The abscess cavity has poor blood supply (surrounded by necrotic tissue) → antibiotics penetrate poorly → need prolonged course for sterilization.

Why no drainage usually? Most lung abscesses drain spontaneously via the bronchial tree (the patient coughs up the pus). Percutaneous drainage risks bronchopleural fistula and empyema. Surgery/drainage reserved for failure to respond.

• Reactive pleural effusion adjacent to pneumonia
• Initially sterile (simple parapneumonic effusion) → may become infected → complicated effusion → empyema

Pus in pleural cavity (gross appearance, Gram's staining or culture). Needs prolonged (4-6 weeks) antibiotics. Pleural drainage (e.g. intercostal tube) is needed.

Key difference from lung abscess: Empyema = pus in the pleural space (needs drainage). Lung abscess = pus in the lung parenchyma (usually drains via bronchi, no external drainage needed).

Electrolyte abnormalities e.g. hypoNa due to SIADH; acute myocardial infarction; cardiac arrhythmia (AF).

Why SIADH in pneumonia? Inflamed lung tissue can produce ADH ectopically → inappropriate water retention → dilutional hyponatraemia. This is especially common with Legionella pneumonia.

Influenza A and B. Immunogenic surface antigens: Haemagglutinin (H) and Neuraminidase (N).

Why H and N matter:

• Haemagglutinin (H): binds sialic acid on host respiratory epithelial cells → mediates viral entry
• Neuraminidase (N): cleaves sialic acid → releases progeny virus from infected cells → allows spread

Antigenic shift: major changes in antigens (e.g. H3N2 to H1N1). Antigenic drift: minor changes in antigens. Worldwide pandemics due to antigenic shift resulting in a new highly pathogenic virus, without specific natural immunity. ^[1]

Why does shift cause pandemics but drift doesn't? Drift causes small changes → most people have partial immunity from prior exposure → seasonal outbreaks. Shift creates an entirely new H or N subtype → nobody has immunity → explosive global spread.

In Hong Kong, influenza is more common from January to March and from July to August.

This is HK-specific and testable — two peaks per year, unlike temperate countries with one winter peak.

URTI symptoms: running nose, sore throat, cough and sputum. Fever, myalgia, arthralgia. Lower respiratory tract or systemic involvement.

Distinguishing influenza from common cold: Influenza has prominent systemic symptoms (high fever, myalgia, prostration) that are disproportionate to respiratory symptoms. Common colds have predominant nasal symptoms with mild or no systemic upset.

Rapid antigen test on NPA, RT-PCR, viral cultures, serology.

• Rapid antigen test: results in 15-30 minutes; moderate sensitivity (~60-70%), high specificity
• RT-PCR: gold standard; high sensitivity and specificity; results in hours
• Viral culture: takes days; mainly for epidemiological surveillance
• Serology: retrospective (paired sera); not useful for acute management

Personal hygiene, symptomatic treatment, specific antivirals.

Pathological dilatation of bronchi. Generalized or localized. Cause: mostly idiopathic (needs to exclude other causes e.g. post-infection, TB).

Why does bronchiectasis develop? The "vicious cycle" hypothesis: infection → inflammation → structural damage to bronchial walls → impaired mucociliary clearance → mucus pooling → further infection → more damage. The end result is irreversible dilation of bronchi.

Causes to exclude:

• Post-infectious: childhood measles/pertussis/severe pneumonia, TB
• Immunodeficiency: hypogammaglobulinaemia, HIV
• Cystic fibrosis (sweat test)
• Primary ciliary dyskinesia (ciliary + sperm analysis)
• Aspiration/GORD (barium studies/pH monitoring)
• Allergic bronchopulmonary aspergillosis (ABPA)
• Autoimmune: RA, SLE

Symptoms:

Chronic sputum production and cough, infective exacerbations, haemoptysis (usually infective), weight loss, fatigue, chest pain, dyspnoea.

Signs:

Cachexia, clubbing, coarse crackles, associated COPD, respiratory failure.

Why clubbing? Chronic suppurative lung disease → likely related to circulating growth factors (VEGF, PDGF) from chronically inflamed tissue → nail bed vasodilation and connective tissue proliferation.

Progressive lung damage, lung abscesses, empyema, brain abscesses.

Why brain abscesses? Right-to-left shunting through the pulmonary circulation (from damaged lung with AV shunting or hypoxia-induced pulmonary hypertension → patent foramen ovale) allows septic emboli to bypass the pulmonary filter → seed the brain. This is a classic exam discriminator.

CXR may be normal or show tramline shadows. HRCT thorax [gold standard]. Immunoglobulins. Auto-antibodies. Barium studies or 24h oesophageal pH monitoring. Ciliary and sperm analysis. Sputum culture and AFB. Neutrophil functions. Sweat test.

• Sputum Gram stain and culture: a good quality specimen should have > 25 PMNs and < 10 squamous epithelial cells per low-power field
• Blood cultures: always two sets (aerobic + anaerobic) from different sites before antibiotics
• MALDI-TOF mass spectrometry increasingly replacing traditional culture for rapid pathogen identification

• Fever = core temperature ≥38.0°C (oral ≥37.5°C)
• Swinging/hectic fever pattern: suggestive of abscess or empyema (wide temperature fluctuations)

• CXR for pneumonia: look for consolidation, air bronchograms, pleural effusion, cavity/air-fluid level
• CT thorax: for complications (abscess, empyema, underlying tumour) and for bronchiectasis diagnosis (HRCT)

• From respiratory DI sessions ^[8]: Interpreting ABG in the context of pneumonia:
  • Type 1 respiratory failure: low PaO₂, normal/low PaCO₂ (pneumonia)
  • Type 2 respiratory failure: low PaO₂, high PaCO₂ (severe pneumonia with exhaustion, or underlying COPD)

1. A 45-year-old diabetic presents with high fever, cough with currant-jelly sputum, and RUL consolidation. Most likely pathogen?

   • Answer: Klebsiella pneumoniae (currant-jelly sputum + diabetic/alcoholic + upper lobe predilection)

2. A 70-year-old nursing home resident develops fever 5 days after hospital admission. Which antibiotic is most appropriate?

   • Answer: Piperacillin-tazobactam (Tazocin) — HAP requires coverage of Gram-negatives including Pseudomonas

3. Which influenza antiviral is effective against both influenza A and B?

   • Answer: Neuraminidase inhibitors (oseltamivir, zanamivir)

4. What is the CURB-65 threshold for hospital admission?

   • Answer: Score ≥2

5. List 5 complications of pneumonia. (10 marks)

   • Respiratory failure, septicaemia/multi-organ failure, lung abscess, parapneumonic effusion/empyema, SIADH with hyponatraemia, AF, acute MI

6. A patient with bronchiectasis has recurrent exacerbations despite standard treatment. Name two long-term pharmacological strategies.

   • Long-term macrolides (azithromycin) for immunomodulation; inhaled anti-pseudomonal antibiotics (if colonized)

7. List 5 predisposing factors for aspiration pneumonia. (10 marks)

   • Altered consciousness, alcoholism, dysphagia/oesophageal disease, bulbar palsy, nasogastric tube feeding, vomiting, severe dental infection, drowning, terminal illness

8. A 61-year-old chronic smoker with previous TB presents with acute greenish sputum and haemoptysis. Name 5 physical examination findings suggesting respiratory failure.
   • Tachypnoea, use of accessory muscles, cyanosis (central), tachycardia, confusion/altered consciousness, oxygen desaturation (SpO₂ < 92%), asterixis (CO₂ retention flap), inability to speak in full sentences ^[3]