What does epidemic mean?
An epidemic is a sudden increase in the number of cases of an infectious disease above what is normally expected in a particular community or region, occurring at the same time and spreading quickly from person to person. The term is central to public health: authorities monitor case counts to decide when an outbreak has crossed the threshold into an epidemic, triggering measures such as vaccination campaigns, quarantines, and travel restrictions. Beyond medicine, the word is widely used figuratively to describe any undesirable phenomenon that spreads rapidly through a population, as in 'an epidemic of gun violence' or 'an obesity epidemic'. It should be distinguished from related terms: an endemic disease is persistently present at low levels in a region, while a pandemic is an epidemic that has spread across countries or continents to affect much of the world. Derived forms such as epidemiology — the study of how diseases spread — show how deeply this word shapes modern health science.
A rapid and widespread outbreak of an infectious disease affecting many individuals in a community or region at the same time.
"The 1918 influenza epidemic killed millions worldwide before it subsided."
Strictly, an epidemic refers to a regional or local surge in cases; a global, multi-continent spread is termed a pandemic.
(Of a disease) prevalent and spreading rapidly among many people in a community at the same time.
"Cholera was epidemic throughout the crowded port city that summer."
Standard regular plural. Often used when discussing historical outbreaks across different times or places.
"History records several devastating epidemics, from the Black Death to smallpox in colonial America."
The word 'epidemic' comes from the Greek for 'upon the people' — literally a disease landing on a population — which is why epidemiologists are, etymologically speaking, people who study what falls upon us all.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of epidemic
Epidemic derives from Greek epidēmos, meaning 'upon the people' or 'prevalent among the people', formed from epi ('upon') and dēmos ('people'). It entered English via Latin and French in the early 17th century, initially as an adjective describing diseases prevalent in a population before settling into its familiar noun use. The same Greek root dēmos gives English words such as demography, demotic, and democracy, while epidemiology — the scientific study of disease distribution — is its most prominent modern descendant.
Related word forms
How epidemic is actually used
Epidemic is neutral in register and appears in both formal medical writing and everyday journalism. In figurative use it often carries a negative connotation, framing a problem as out of control. It is typically applied to diseases affecting many people in one area; once spread becomes global, 'pandemic' is preferred.
Easily confused with epidemic
An epidemic is confined to a particular community or region, whereas a pandemic spreads across multiple countries or continents and affects a very large proportion of the world's population.
An epidemic is a sudden surge in disease cases, while endemic describes a disease that is constantly present at a baseline level in a particular population or region.