Pandemic, Epidemic, and Endemic: What Do These Terms Mean?

The words “pandemic,” “epidemic,” and “endemic” show up in the news in reference to virus outbreaks and public health crises. But what do all these terms actually mean? Here’s what you need to know.

To understand the terms clearly in their scientific context (and not the imprecise way in which they’re sometimes thrown around), you have to go to the source. Epidemiology is the study of diseases in human and animal populations that focuses on how, when, and where diseases spread. Epidemiologists also analyze associated risk factors, identify preventive methods, and help in the development of health policies and community education.

They base their research on two measurable factors: reproduction rate (the occurrence of the disease over a given period of time) and critical community size (the prevalence of the disease within a given population).

Based on this information, infectious diseases (the kind you can catch) are classified in the following ways:

• Endemic: The constant presence of a disease at a predictable rate within a given area or population. Endemic diseases are notable for their continued, stable presence. Chicken pox is one example; it occurs at a predictable rate among school children.
• Epidemic: The sudden and rapid spread of a disease within one or multiple communities at a particular time. Ebola, which spread across Western Africa from 2013 through 2016, was an epidemic.
• Pandemic: An epidemic that has spread from a particular region and now affects thousands (or even millions) of people in multiple countries. For example, the swine flu (H1N1) affected millions all over the world and caused 151,000-575,000 fatalities according to the CDC‘s estimates.

The best way to minimize your chance of contracting any of these types of diseases is to frequently wash your hands. Also, avoid touching your face with your hands, as you might have unknowingly touched an infected surface.

According to the CDC, the most effective way to avoid contracting any of these types of diseases is to avoid busy areas and potentially infected people. This, coupled with consistently washing your hands thoroughly, is a much better way to protect yourself than a surgical mask.