What is the study of how diseases spread in populations called?

What is the study of how diseases spread in populations called? Epidemiology is the field.

Epidemiology examines the distribution, patterns, causes, and determinants of health conditions in defined populations. It asks who is affected, where and when cases occur, which exposures or behaviors may raise risk, and how prevention can reduce illness. Although often associated with outbreaks, epidemiology also studies chronic diseases such as cancer, diabetes, and cardiovascular disease.

Descriptive epidemiology measures patterns by person, place, and time. Analytic epidemiology tests possible explanations using methods such as cohort studies and case-control studies. During an outbreak, epidemiologists may combine surveillance, interviews, laboratory data, contact tracing, and statistical analysis to identify sources and interrupt transmission.

A common mix-up is treating epidemiology as the study of individual patients. Clinical medicine focuses primarily on diagnosing and treating a person; epidemiology focuses on patterns across groups. The term is also broader than infectious disease: it can examine injuries, mental illness, environmental exposures, treatments, and social determinants of health.