Pulmonary Infections (Tuberculosis, Pneumonia, Fungal and Parasitic Disease)
Domain 4 - Pulmonary Infections
This domain covers tuberculosis, community- and hospital-acquired pneumonia, fungal disease and parasitic pulmonary infections. The exam tests pragmatic diagnosis: which specimen to send, when imaging is enough, how to choose empirical antibiotics, and how to recognise treatment failure or drug resistance.
Core rules
- Active pulmonary TB: sputum AFB smear, Xpert MTB/RIF or Ultra, and culture. Xpert detects TB and rifampicin resistance; culture confirms viability and susceptibility. IGRA and tuberculin skin test cannot distinguish latent from active disease.
- Drug-susceptible TB: 2 months isoniazid, rifampicin, pyrazinamide and ethambutol, then 4 months isoniazid and rifampicin (2HRZE/4HR). Adherence support and contact tracing are mandatory.
- CAP severity: CURB-65 (confusion, urea >7 mmol/L, respiratory rate ≥30, systolic BP <90 or diastolic ≤60, age ≥65). Score 0–1 outpatient; 2 short admission or supervised outpatient; ≥3 inpatient, consider ICU.
- Empirical CAP therapy: healthy outpatient amoxicillin or doxycycline; comorbidity beta-lactam plus macrolide or respiratory fluoroquinolone; severe beta-lactam plus macrolide or beta-lactam plus fluoroquinolone.
- Fungal disease: aspergilloma in a pre-existing cavity; ABPA in asthma with eosinophilia, high IgE and central bronchiectasis; invasive aspergillosis in prolonged neutropenia. Pulmonary hydatid cysts require careful surgery or PAIR, not simple aspiration.
Worked example
A 70-year-old man has fever, cough and confusion. Urea is 10 mmol/L, respiratory rate 32/min, BP 88/60 mmHg, and age 70. CURB-65 score is 5 (confusion, urea, respiratory rate, blood pressure, age), predicting high mortality. Admit to hospital, assess for ICU, take blood and sputum cultures, and start empirical ceftriaxone plus azithromycin, adjusting to local resistance and severity. Add influenza testing and oxygen. Do not delay antibiotics for a procalcitonin result.
Traps that cost marks
- Using a positive IGRA to diagnose active TB.
- Sending only one sputum sample or accepting smear negativity as exclusion of TB.
- Treating a CURB-65 score of 2 as automatically outpatient without clinical judgement.
- Missing rifampicin resistance on Xpert and starting standard therapy in a high-risk patient.
- Aspirating a suspected hydatid cyst without precautions because of anaphylaxis risk.
Key points
- Xpert MTB/RIF detects TB and rifampicin resistance; culture confirms susceptibility.
- Standard TB regimen is 2HRZE/4HR.
- CURB-65 ≥3 means inpatient care; score 5 needs ICU assessment.
- Severe CAP: beta-lactam plus macrolide or beta-lactam plus fluoroquinolone.
- ABPA: asthma, eosinophilia, high IgE, central bronchiectasis.