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JAMA Patient Page
March 5, 2019

What Is a Pandemic?

JAMA. 2019;321(9):910. doi:10.1001/jama.2019.0700

The terms endemic, outbreak, epidemic, and pandemic indicate how common a condition is at a point in time relative to how common it was at an earlier time.

The terms endemic, outbreak, epidemic, and pandemic are often used to describe infections, although conditions such as hypertension, cancer, violence, or even positive, beneficial behaviors can also be described the same way. These categories are primarily based on how many cases of a condition there are compared with the expected number of cases over a given time and how far the cases have spread geographically.

An endemic condition is present at a fairly stable, predictable rate among a group of people—the observed number of cases are approximately the same as the number expected. The group of people might be all the inhabitants of a town or county, or larger areas like countries or continents. Examples include malaria in Africa, coccidioidomycosis in the southwestern United States and northern Mexico, dengue in tropical and subtropical regions, and hepatitis B worldwide, although rates are higher in Asia and Africa (high endemicity) than in Europe and North America (low endemicity).