1: Definition/history of epidemiology

Section 1: Foundations - Definition/History of Epidemiology

Definition:

Epidemiology is the foundational science of public health, defined as the study of the distribution (who, when, and where) and determinants (why and how) of health-related states or events (including diseases, injuries, and wellness) in specified populations. Its core purpose is to apply findings to control health problems. Key elements include:

• Exposure: Any factor (biological, chemical, behavioral) potentially influencing health.
• Outcome: The health event being studied (e.g., disease onset).
• Population focus: Analyzing patterns across groups, not individuals.

Historical Evolution:

Ancient Foundations (5th Century BCE–17th Century):

• Hippocrates (Greece, 400 BCE) first linked disease to environmental factors in "On Airs, Waters, and Places", rejecting supernatural causes.
• Thucydides documented the Athenian plague (430 BCE), noting immunity in survivors—an early observation of natural immunity.

Quantitative Beginnings (17th–18th Century):

• John Graunt (England, 1662) analyzed London mortality bills, creating the first life tables and noting sex/age disparities in death rates—pioneering vital statistics.
• James Lind (1747) conducted a controlled trial on scurvy in sailors, comparing treatments (e.g., citrus vs. vinegar) and establishing early experimental principles.

Modern Foundations (19th Century):

• John Snow (London, 1854) investigated cholera as a "natural experiment." By mapping cases and water pump use, he implicated the Broad Street pump, demonstrating disease transmission via contaminated water—fundamental to environmental epidemiology.
• William Farr systematized death registration, developing early surveillance systems and statistical analyses of mortality data.

Germ Theory & Chronic Disease Shift (Late 19th–Mid-20th Century):

• Robert Koch and Louis Pasteur’s germ theory (1870s–1880s) shifted focus to infectious agents. Koch’s postulates (criteria for causation) became vital tools.
• Mid-20th century saw epidemiology expand beyond infections. The Framingham Heart Study (1948) identified risk factors (e.g., hypertension, smoking) for cardiovascular disease. Richard Doll and Austin Bradford Hill (1950s) linked smoking to lung cancer using cohort studies, cementing analytical methods for chronic diseases.

Modern Scope:

Today, epidemiology spans infectious outbreaks (COVID-19), chronic diseases (cancer), genetic/environmental interactions, social determinants of health, and global health equity. Its methods underpin evidence-based medicine and health policy, evolving continuously through technological advances (e.g., genomic sequencing, big data).