Infectious Diseases
Core framework
Build answers around syndrome, host, and organism - then apply antimicrobial stewardship. Know the sepsis bundle (cultures before antibiotics, lactate, fluids, vasopressors for refractory hypotension) and the principles of source control. For each major syndrome (meningitis, pneumonia, urinary sepsis, endocarditis, bone and joint infection, HIV-related opportunistic disease), know the common organisms and first-line empiric therapy.
Concepts examiners test
Meningitis: immediate empiric therapy with dexamethasone timing, and cerebrospinal fluid interpretation (bacterial versus viral versus tuberculous patterns). Endocarditis: blood culture technique and echocardiography. Tuberculosis: diagnosis, isolation, and drug interactions. HIV: when to start antiretroviral therapy, prophylaxis thresholds (CD4 counts for Pneumocystis, toxoplasmosis, Mycobacterium avium complex), and immune reconstitution inflammatory syndrome. Also: malaria diagnosis and treatment, dengue warning signs, brucellosis, and antimicrobial resistance mechanisms.
Traps
- Do not delay antibiotics for lumbar puncture in suspected bacterial meningitis; draw blood cultures and treat.
- Dexamethasone before or with the first antibiotic dose in suspected pneumococcal meningitis.
- Rifampicin is a potent enzyme inducer - check interactions with oral contraceptives and antiretrovirals.
- Immune reconstitution inflammatory syndrome can mimic treatment failure; do not stop antiretroviral therapy reflexively.
- Prophylaxis thresholds for opportunistic infection depend on CD4 count, not viral load alone.
Worked rule of thumb
A patient with fever, neck stiffness and altered consciousness: start empiric ceftriaxone plus vancomycin (plus ampicillin if listeria risk) and dexamethasone, take blood cultures, and proceed to lumbar puncture when safe. Do not delay treatment for imaging unless focal signs or immunosuppression demand it.