Infectious Diseases
The exam focuses on sepsis recognition, empiric antibiotic choice, cerebrospinal fluid interpretation, tuberculosis and HIV-related opportunistic infection.
Sepsis
Sepsis is life-threatening organ dysfunction from infection, defined by a SOFA rise of 2 or more. Septic shock is vasopressor-requiring hypotension with lactate above 2 mmol/L despite adequate fluid. The first hour should include blood cultures, lactate, broad-spectrum antibiotics and 30 mL/kg crystalloid for hypotension or lactate of 4 mmol/L or more.
Meningitis
Bacterial cerebrospinal fluid shows a glucose ratio below 0.4, protein above 200 mg/dL and neutrophil predominance; viral shows lymphocytosis with normal glucose; tuberculous shows lymphocytosis, low glucose and very high protein. Give dexamethasone with or just before the first antibiotic dose in suspected pneumococcal meningitis. Do not delay antibiotics for lumbar puncture when the patient is unstable.
Tuberculosis
Interferon-gamma release assays cannot distinguish latent from active disease; use sputum Xpert MTB/RIF as the initial test for suspected pulmonary TB.
HIV
Screen opportunistically. Pneumocystis pneumonia is treated with high-dose trimethoprim-sulfamethoxazole; start antiretroviral therapy early, within two weeks of most opportunistic infections.
Worked example
A patient with fever, neck stiffness and CSF glucose 28 mg/dL against a serum glucose of 110 mg/dL, protein 240 mg/dL and 90% neutrophils has bacterial meningitis. Give dexamethasone and empiric ceftriaxone plus vancomycin immediately, before imaging if there are no focal signs.
Traps that cost marks
- Delaying antibiotics while awaiting lumbar puncture or CT.
- Treating asymptomatic bacteriuria in a catheterised patient.
- Missing that IGRA positivity does not prove active TB.