Core Curriculum
Module 1: Epidemiology & Population Health
Core Topics
Foundational concepts: disease frequency, health status metrics, survival analysis, population pyramids, outbreak investigation, herd immunity, and prevention levels. Essential for understanding disease distribution and public health interventions.
📊 1.1 Measures of Disease Frequency
Incidence & Prevalence
Incidence measures new cases over time; prevalence measures existing cases at a point or period. Key relationship: Prevalence ≈ Incidence × Average Disease Duration (stable conditions).
Cumulative incidence = (Number of new cases) / (Population at risk at start) × time period
Incidence rate (density) = (Number of new cases) / (Person‑time at risk)
Point prevalence = Total existing cases / Total population at one time
Period prevalence = Cases during time interval / Average population during interval
📌 Clinical pearl: Chronic diseases (e.g., diabetes) have high prevalence despite low incidence due to long duration; acute diseases (e.g., common cold) have low prevalence despite high incidence because they resolve quickly.
📈 1.2 Measures of Health Status
Mortality, Morbidity & Reproductive Rates
Mortality measures
Crude death rate = (Total deaths / Total pop) × multiplier
Case fatality rate = (Deaths from disease / Total cases) × 100
Age‑specific / cause‑specific rates
Reproductive rates
Maternal mortality ratio = (Maternal deaths / Live births) × 100,000
Infant mortality rate = (Deaths <1 year / Live births) × 1,000
Neonatal, perinatal, under‑5 mortality
Standardization & Life Expectancy
Direct standardization applies age‑specific rates to a standard population. Indirect standardization calculates SMR = Observed deaths / Expected deaths × 100.
SMR > 100 → excess mortality; SMR < 100 → lower mortality than standard.
Health‑Adjusted Life Expectancy (HALE): years lived in full health. Disability‑free life expectancy also used.
⚠️ 1.3 Population Impact Measures
PAR, YPLL, QALYs, DALYs
Population Attributable Risk (PAR) = Incidencetotal – Incidenceunexposed (excess burden due to exposure).
Years of Potential Life Lost (YPLL) = Σ (reference age – age at death) for premature deaths; prioritizes conditions affecting younger populations.
Quality‑Adjusted Life Years (QALYs) = Years of life × utility weight (0=death, 1=perfect health); used in cost‑effectiveness.
Disability‑Adjusted Life Years (DALYs) = Years of Life Lost (YLL) + Years Lived with Disability (YLD); measures total burden of disease.
📊 Global burden: DALYs combine mortality and morbidity into a single metric, guiding WHO priorities.
📉 1.4 Survival Analysis
Kaplan‑Meier & Hazard Ratio
Kaplan‑Meier curves estimate survival probability over time, handling censored data (tick marks). Log‑rank test compares survival distributions between groups.
Hazard Ratio (HR) = instantaneous risk in one group / risk in another. HR < 1 indicates lower hazard (protective).
📌 Clinical applications: cancer survival, graft survival, time to cardiovascular events. Curves crossing suggest time‑dependent effect.
👥 1.5 Population Pyramids & Demographic Changes
Expansive (pyramid)
Wide base, high birth/death rates → young population. Healthcare: maternal‑child, infectious diseases, vaccines.
Constrictive (inverted)
Narrow base, aging population → low birth rate, low mortality. Healthcare: chronic diseases, geriatrics.
Stationary (column)
Stable, low birth & death rates → mixed needs transitioning to chronic disease focus.
Demographic transition: Stages from high birth/death rates (pre‑industrial) to very low rates (post‑industrial). Dependency ratio = (population <15 + ≥65) / (population 15‑64). Aging populations increase chronic disease burden.
🕵️ 1.6 Disease Surveillance & Outbreak Investigation
Surveillance Types
Passive: routine provider reporting (underreporting common). Active: health officials seek cases (more complete). Sentinel: selected sites report trends. Syndromic: pre‑diagnosis symptoms (early warning).
Outbreak Investigation Steps
- Verify diagnosis & existence
- Define & identify cases (case definition)
- Describe by person, place, time (epidemic curve)
- Develop hypotheses
- Test hypotheses (analytical studies)
- Implement control measures
- Communicate findings
Epidemic curves: Point source → sharp peak; Continuous common source → plateau; Propagated → progressive peaks (person‑to‑person).
🦠 1.7 Communicable Disease Transmission
Attack rate = (Number ill / Number at risk) × 100
Secondary attack rate = (Cases among contacts / Total contacts) × 100
Herd immunity threshold = 1 – (1 / R₀), where R₀ = basic reproduction number.
Example: Measles (R₀ = 12–18) → threshold 92–95%; COVID‑19 (R₀ ≈ 2–3) → 50–67%.
Vaccine effectiveness (VE) = [(ARunvacc – ARvacc) / ARunvacc] × 100
📌 Reportable diseases: Immediately reportable: anthrax, plague; within 24h: measles, pertussis; routine: HIV, TB, hepatitis.
🛡️ 1.8 Points of Intervention & Prevention
Primary prevention
Prevent disease before onset: vaccination, health education, smoke‑free laws, chemoprophylaxis (PrEP).
Secondary prevention
Early detection: screening (mammography, colonoscopy), contact tracing, surveillance.
Tertiary prevention
Reduce complications: rehabilitation, cardiac rehab, disease management programs.
Community‑Level Interventions
- Policy: cigarette taxes, soda taxes, smoke‑free public places, alcohol pricing.
- Environmental: farmers markets, bike lanes, clean air regulations, safe playgrounds.
- School: PE requirements, healthy lunch programs, mental health services.
⚖️ Effectiveness: Population reach vs. individual impact; health equity; cost‑effectiveness; political feasibility; unintended consequences.