Respiratory Infections

Pneumonia

Community-Acquired Pneumonia (CAP)

•    Common pathogens:

o    Streptococcus pneumoniae (most common)

o    Haemophilus influenzae

o    Atypicals: Mycoplasma pneumoniae, Legionella pneumophila, Chlamydophila pneumoniae

•    Investigations:

o    CXR (lobar consolidation)

o    Sputum culture, blood cultures

o    Urine antigen: Legionella, S. pneumoniae

•    Severity assessment — CURB-65:

o    Confusion (AMT <8)

o    Urea >7 mmol/L

o    Respiratory rate ≥30

o    BP <90 systolic or ≤60 diastolic

o    Age ≥65

o    Score ≥2 → consider hospital admission

•    Treatment (based on severity/local guidelines):

o    Mild: amoxicillin ± clarithromycin/doxycycline

o    Moderate/severe: IV co-amoxiclav + clarithromycin

Hospital-Acquired Pneumonia (HAP)

•    Occurs ≥48 hours after hospital admission

•    Common organisms:

o    Gram-negatives: E. coli, Klebsiella, Pseudomonas

o    MRSA

•    Treatment:

o    Early onset (<5 days): co-amoxiclav

o    Late onset or risk of resistance: piperacillin–tazobactam, meropenem ± vancomycin

Empyema

•    Pus in pleural space, often complication of pneumonia

•    Diagnostic features (pleural fluid):

o    pH <7.2

o    ↓ glucose

o    ↑ LDH

o    Positive Gram stain or culture

•    Management:

o    Chest tube drainage

o    Prolonged antibiotics (2–4 weeks)

o    Surgical referral if loculated

Tuberculosis (TB)

•    Clinical features:

o    Cough >3 weeks, haemoptysis, weight loss, fever, night sweats

o    Risk: immunosuppressed, close contacts, migrants from endemic areas

•    Imaging:

o    CXR: apical infiltrates, cavitation, hilar lymphadenopathy, miliary pattern

•    Diagnosis:

o    Sputum: Ziehl–Neelsen stain (acid-fast bacilli), culture (Lowenstein–Jensen), NAAT

o    IGRA (Interferon Gamma Release Assay): screen latent TB

•    Treatment (RIPE):

o    Rifampicin: orange secretions, enzyme inducer

o    Isoniazid: neurotoxicity → give pyridoxine (B6)

o    Pyrazinamide: hepatotoxicity, hyperuricaemia

o    Ethambutol: optic neuritis

o    Duration: 6 months (2 months RIPE, then 4 months R + I)

Bronchiectasis

•    Permanent dilation of bronchi → chronic productive cough, recurrent infections

•    Causes:

o    Cystic fibrosis

o    Post-infectious (e.g., measles, pertussis, TB)

o    Primary ciliary dyskinesia (Kartagener’s syndrome)

o    Hypogammaglobulinaemia

•    Diagnosis:

o    HRCT: "tram-track" or "signet-ring" appearance

o    Sputum cultures

•    Management:

o    Chest physiotherapy (postural drainage)

o    Antibiotics (guided by cultures; azithromycin prophylaxis if frequent exacerbations)

o    Bronchodilators if coexisting airflow obstruction

Cystic Fibrosis (CF)

•    Autosomal recessive mutation in CFTR gene (ΔF508 most common)

•    Defective chloride channel → thick mucus → recurrent infections, pancreatic enzyme insufficiency, male infertility

•    Respiratory: Pseudomonas aeruginosa, S. aureus, bronchiectasis

•    GI: pancreatic insufficiency (fatty stools), CF-related diabetes, meconium ileus in neonates

•    Other: nasal polyps, infertility (bilateral absence of vas deferens)

•    Diagnosis:

o    Newborn screening

o    Sweat chloride test >60 mmol/L

•    Management:

o    Chest physiotherapy, mucolytics (dornase alfa)

o    Antibiotics (oral/inhaled/IV for exacerbations)

o    Pancreatic enzyme replacement

o    CFTR modulators (e.g., ivacaftor, lumacaftor)

Aspergillus-Related Lung Disease

Allergic Bronchopulmonary Aspergillosis (ABPA)

•    Asthma or CF patients

•    Features: wheeze, cough, eosinophilia, fleeting infiltrates, central bronchiectasis

•    Diagnosis:

o    ↑ total IgE

o    Positive Aspergillus skin test/IgE/IgG

•    Treatment: steroids ± itraconazole

Aspergilloma

•    Fungal ball in pre-existing cavity (e.g., post-TB)

•    Often asymptomatic but can cause haemoptysis

•    CXR: "air crescent" sign

•    Treatment: surgery if severe haemoptysis

Invasive Aspergillosis

•    Occurs in immunocompromised (e.g., neutropenia, transplant)

•    Features: fever, cough, haemoptysis, pleuritic pain, may disseminate

•    Imaging: halo sign or cavitating nodules on CT

•    Treatment: voriconazole, amphotericin B (severe)

Extra Revision Pearls

•    Rust-coloured sputum → S. pneumoniae

•    Dry cough + autoimmune haemolysis → Mycoplasma pneumoniae

•    Diarrhoea + hyponatraemia + confusion → Legionella

•    CF patients → chronic Pseudomonas infection risk, nasal polyps clue

•    Clubbing in bronchiectasis, TB, and lung abscess; uncommon in COPD or asthma

•    Miliary TB → think immunosuppression, HIV

•    Empyema pleural fluid glucose often <3.3 mmol/L

•    ABPA clue: asthma patient with fleeting infiltrates + eosinophilia + high IgE