Epidemiology and Public Health: Key Concepts and Historical Figures

Father of modern medicine

Hippocrates

Dr. Semmelweis's contribution

Introduced handwashing to prevent childbed fever

Disease studied by Semmelweis

Childbed fever, linked to bacteria on physicians' tools

John Snow's contribution to epidemiology

Traced a cholera outbreak to contaminated water in London

Robert Koch's contribution

Developed germ theory, identified TB and cholera agents, proposed Koch's postulates

Doll & Hill experiment

Study linking smoking to lung cancer

Three levels of prevention in epidemiology

Primary, secondary, tertiary

Active vs passive primary prevention

Active requires personal effort (vaccination), passive does not (fluoridated water)

Example of primary prevention

Vaccination

Example of secondary prevention

Screening (e.g., echocardiography, Pap test)

Example of tertiary prevention

Rehabilitation, preventing complications

Prevention phase associated with pathogenesis

Secondary prevention (subclinical stage)

Active immunity

Exposure to antigen (long-lasting)

Passive immunity

Antibodies from another source (short-term)

Immunity provided by DTaP and Tdap vaccines

Active immunity

Herd immunity

Population-level protection when enough individuals are immune

Incidence

New cases of disease

Cumulative incidence

New cases ÷ total population at risk over a time period

Incidence density

New cases ÷ person-time at risk (used for open populations)

Prevalence

Total cases (point or period) ÷ population

Crude death rate formula

Deaths ÷ population × 1,000

Case fatality rate

Deaths from a disease ÷ diagnosed cases

Infant mortality rate

Deaths in children under 1 year ÷ live births in same time period

Maternal mortality rate

Maternal deaths from pregnancy-related causes ÷ live births

Disease-specific mortality rate

Deaths from a specific cause ÷ population

Attack rate

New cases ÷ population at risk (often for outbreaks, e.g., foodborne illness)

Sensitivity

Proportion of true positives identified

Specificity

Proportion of true negatives identified

Positive predictive value (PPV)

Probability that a positive test is truly positive

Negative predictive value (NPV)

Probability that a negative test is truly negative

False positive vs false negative

FP: test positive but no disease; FN: test negative but disease present

Lead time bias

Early detection appears to improve survival but does not change outcome

Advantages of mass screening

Detects disease early but expensive, may cause overdiagnosis

Advantages of selective screening

Focuses on high-risk groups, but misses cases in general population

Fomite

Inanimate object that transmits pathogens (e.g., phone, doorknob)

Main modes of transmission

Direct (person-to-person) and indirect (fomite, airborne, vehicle, vector)

Vector-borne disease

Illness transmitted by organisms like mosquitoes or ticks (e.g., malaria, leishmaniasis)

Carriers

Individuals who harbor pathogens without symptoms (asymptomatic, incubatory, convalescent, chronic)

Epidemiologic triad

Agent, host, environment. Example: host factor = vaccination status

Epidemiology

Study of the distribution and determinants of health-related events in populations

Difference between morbidity and mortality

Morbidity = illness; Mortality = death

Endemic, epidemic, and pandemic

Endemic = constant in region; Epidemic = above expected; Pandemic = worldwide spread

Surveillance

Ongoing collection, analysis, and dissemination of health data (active vs passive)

Survival analysis

Method to study time until an event occurs (death, recurrence)

Stages of disease

Prepathogenesis (before onset), pathogenesis (disease development), late pathogenesis (outcomes)