Epidemic describes disease spreading quickly through a large part of the population — and as a noun, an outbreak of a disease on that scale. Epidemiologists define it as cases clearly in excess of what is normally expected in a community or region: a foodborne outbreak that sickens hundreds across several cities is an epidemic, as is the seasonal surge of norovirus. The word’s food applications are concrete — cholera epidemics traced to water, E. coli epidemics traced to produce — and investigation follows the classic pattern: case definition, descriptive epidemiology, hypothesis, analytical study, control. Beyond infection, the term stretches to the “obesity epidemic” and the “diabetes epidemic,” using epidemic language for non-communicable conditions spreading through populations. Whether microbial or metabolic, an epidemic is disease moving faster than the systems meant to contain it.