Scientists Say: Outbreak, Epidemic and Pandemic

These terms can describe what is happening as a disease spreads

During a disease outbreak, people sometimes wear masks to try to protect themselves. Masks can prevent infected people from spreading germs. But when worn by healthy people, it’s not clear how much masks help.

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Outbreak, epidemic and pandemic (nouns, “OWT-BRAKE,” “EHP-ih-DEM-ick” and “PAN-dem-ick”)

When an infectious disease starts to spread, experts can use several terms to describe this. An outbreak is an unexpected number of cases. It can be limited to a single community. It might even be just one case. Or it can spread across countries. It can last just a few days or persist for years.

In March 2014, the World Health Organization reported an outbreak of Ebola in west Africa. Then the disease spread to several countries. Now it was as an epidemic. Epidemic diseases spread rapidly and infect many people.

Some diseases spread to infect many people in countries over several continents. These are known as pandemics. Ebola never reached pandemic status because it was confined to one region of Africa. And pandemics of new diseases are rare. But those rare cases can be devastating since no one is immune to an illnesses that has never before infected people.

Influenza spreads around the world every year in a pandemic. A very bad influenza pandemic developed in 1918 and 1919. It spread to an estimated 500 million people. That was roughly one in every three people alive at that time. This pandemic killed an estimated 50 million people.

In a sentence

Scientists have found DNA in ancient teeth from the germs that caused epidemic and pandemic plague. But plague is not just a disease of the past; outbreaks still occur today.

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Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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