Infectious Diseases
This block tests time-critical sepsis care, central nervous system infection, and infections with strong regional epidemiology, including brucellosis and tuberculosis.
Sepsis
The hour-1 bundle: measure lactate, draw blood cultures before antibiotics, give broad-spectrum antibiotics within one hour in septic shock, give 30 mL/kg crystalloid for hypotension or lactate ≥4, and start norepinephrine to keep MAP ≥65 mmHg.
Bacterial meningitis
Give dexamethasone 10 mg IV with or just before the first antibiotic dose, and do not delay antibiotics for lumbar puncture. Empiric therapy: vancomycin plus ceftriaxone, adding ampicillin when the patient is over 50 or immunocompromised. Lumbar puncture is deferred for papilloedema, focal deficit, seizures, coagulopathy, or local skin infection.
Regionally important infections
- Brucellosis: undulant fever, sacroiliitis, hepatosplenomegaly, unpasteurised dairy exposure. Treat with doxycycline plus rifampin or streptomycin for at least 6 weeks; relapse is common.
- Tuberculosis: sputum AFB, culture, and PCR; standard regimen 2 months of rifampin, isoniazid, pyrazinamide, ethambutol, then 4 months of rifampin and isoniazid.
- Infective endocarditis: Duke criteria; three blood cultures from separate sites before antibiotics; surgery for heart failure, uncontrolled infection, or large vegetation.
- HIV post-exposure prophylaxis: start within 72 h and continue 28 days.
Worked example
A 28-year-old farmer has three weeks of undulant fever and low back pain, and Rose Bengal is positive. Start doxycycline plus streptomycin for 6 weeks rather than a short course, because intracellular organisms and osteoarticular foci drive relapse. Reasoning: exposure history plus focal bone pain defines the treatment duration, not the culture turnaround.
Traps that cost marks
- Performing lumbar puncture before antibiotics in a patient with papilloedema.
- Treating brucellosis with a single agent or a short course.
- Missing that Staphylococcus aureus bacteraemia requires source control.