Infectious Diseases, Epidemiology, and Immunoprophylaxis
What candidates must know
This domain combines clinical infectiology with population-level prevention. Know the presentation and management of common infections: respiratory (influenza, pneumonia, tuberculosis), enteric (hepatitis A and B, salmonellosis), vector-borne, and bloodborne (HIV, hepatitis B and C). Understand isolation precautions - contact, droplet, airborne - and when each applies. Epidemiology requires incidence versus prevalence, attack rate, relative and attributable risk, sensitivity and specificity, and outbreak investigation steps. Immunoprophylaxis covers the national immunization schedule, vaccine types (live attenuated versus inactivated), cold chain, contraindications, and adverse event reporting.
Traps in questions
Incidence and prevalence are frequently confused: incidence measures new cases over time, prevalence measures all existing cases at a point. Sensitivity and specificity questions often ask about a screening test in a low-prevalence population, where positive predictive value falls despite high specificity. Vaccine traps include giving live vaccines to immunocompromised patients or during pregnancy, and misidentifying a true contraindication versus a precaution. Tuberculosis questions may test the difference between latent infection and active disease.
Worked example: rule of thumb
A test with 95% sensitivity and 90% specificity used in a population with 1% prevalence will yield many false positives; the positive predictive value is low. Rule of thumb: high sensitivity rules out disease (SnNout), high specificity rules in (SpPin). For isolation: airborne precautions for tuberculosis, measles, and varicella; droplet for influenza and meningococcus; contact for multidrug-resistant organisms and Clostridioides difficile.