Community Health, Public Health and Epidemiology Basics
This domain tests how disease is measured in populations and how national programmes use that information.
Epidemiology defined
Epidemiology is the study of the distribution and determinants of health-related states in populations, and the application of that study to control health problems.
Incidence and prevalence
Incidence counts new cases arising in a population at risk during a defined period; it measures risk. Prevalence counts all existing cases at a point or over a period; it measures burden and depends on how long the disease lasts.
Standard rates
Crude birth rate and crude death rate are per 1,000 population per year. Infant mortality rate = infant deaths under one year ÷ live births × 1,000. Maternal mortality ratio = maternal deaths ÷ 100,000 live births. Total fertility rate is the average number of children per woman.
Occurrence patterns
Endemic (constant presence), epidemic (clear excess in a area or time), pandemic (global spread), sporadic (occasional isolated cases).
Screening tests
Sensitivity = true positives ÷ (true positives + false negatives) - the ability to detect disease. Specificity = true negatives ÷ (true negatives + false positives) - the ability to exclude it. Positive predictive value depends heavily on prevalence.
Worked example
A village of 1,000 people has 20 known diabetics on 1 January and 50 people newly diagnosed during the year. Point prevalence on 1 January = 20 ÷ 1,000 = 2%. Incidence during the year = 50 ÷ 980 population at risk = about 5.1%. Reasoning: prevalence uses all existing cases; incidence uses only new cases and excludes those already diseased from the denominator.
Programmes to name
NTEP for TB, NACP for HIV, NPCDCS for non-communicable diseases, Universal Immunisation Programme; ASHA, VHSNC and Rogi Kalyan Samiti at community level.
Traps that cost marks
Calling prevalence a measure of risk; using total population as the incidence denominator; placing maternal deaths over total population instead of live births.