Community Health and Public Health
Community Health and Public Health in the UP NHM CHO paper checks whether you can think in populations, not just patients: measuring disease, preventing it before it starts, and reading a village's water, sanitation and vital statistics.
Levels of prevention
- Primordial - stop risk factors forming in the population (tobacco-free schools, breastfeeding promotion).
- Primary - act before disease in a susceptible person (immunisation, chlorination, condoms, bed nets).
- Secondary - early detection and prompt treatment (screening, VIA, sputum NAAT).
- Tertiary - limit disability and rehabilitate (physiotherapy after stroke, insulin titration).
Core measures
- Incidence = new cases divided by population at risk per unit time. Prevalence = all existing cases divided by total population at a point.
- IMR = infant deaths under 1 year per 1,000 live births in the same year; MMR = maternal deaths per 1,00,000 live births.
- Sensitivity = TP/(TP+FN); specificity = TN/(TN+FP); PPV depends heavily on prevalence.
Worked example
2,000 women are screened; 100 truly have the condition; the test is positive in 90 of them, and falsely positive in 95 of the 1,900 healthy women. Sensitivity = 90/100 = 90%. Specificity = 1,805/1,900 = 95%. PPV = 90/185 ≈ 48.6%. So even a good test produces a positive result that is wrong more than half the time when prevalence is only 5%; screening works because it is followed by a confirmatory test.
Traps
- Using the whole population instead of the population at risk for incidence.
- Reversing numerator and denominator in IMR and MMR - the denominator is always live births.
- Calling screening "primary prevention"; it is secondary.
- Forgetting SnNout and SpPin: a highly sensitive test rules out, a highly specific test rules in.