Community Medicine
What candidates must know
Community medicine addresses health at population level: the determinants of health, disease surveillance, outbreak investigation, screening programme principles, and the organisation of primary care. Understand incidence versus prevalence, sensitivity/specificity/positive predictive value, and the criteria for a worthwhile screening programme (Wilson–Jungner). Know notifiable disease reporting, immunisation programme coverage, and the social determinants of health. Familiarity with the principles of outbreak investigation (case definition, line listing, hypothesis, control) and with health-system concepts - access, equity, and the role of the family physician as gatekeeper - is expected.
Traps in questions
- Incidence vs prevalence: incidence = new cases over time; prevalence = all cases at a point. A longer survival increases prevalence without changing incidence.
- PPV depends on prevalence - a highly specific test in a low-prevalence population still yields many false positives.
- Screening vs diagnosis: screening is for asymptomatic people; a positive screen needs confirmatory testing.
- Lead-time bias can make screening look effective when it merely advances diagnosis.
- Notifiable diseases must be reported; questions test the duty, not the treatment.
Rule of thumb
Think population, then person. Ask whether the question is about an individual's care or a community-level intervention; the correct answer differs sharply between the two.
Worked example
A new rapid test with 99% specificity is used in a population with 1% prevalence. Even with high specificity, the positive predictive value is modest because most positives are false positives - confirmatory testing is essential before acting.