Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Using Correct Terminology Decreases Confusion

Dear Doctor: Would you please explain the terms we keep hearing in news reports about that new virus, like “epidemic” and “outbreak” and “pandemic”? It seems like they’re being used interchangeably, and it makes it hard to understand what’s really going on.

Dear Reader: You are referring to what initially was known as Wuhan coronavirus, a new respiratory illness identified in China at the end of December 2019. The name referred to the city where the illness first appeared and the specific virus that causes it. In mid-February, the World Health Organization officially gave the virus a name -- COVID-19. That breaks down to “CO” for corona, “VI” for virus, “D” for disease, and 19, which indicates the year this new illness appeared.

Your question is important because each of the terms you mention -- outbreak, epidemic and pandemic -- refers to a different type of event. They arise from a branch of medicine known as epidemiology, which is the study of how, where and why disease and illness spread, and how to predict and prevent them. And we agree that misusing these terms can lead to confusion and misunderstanding.

An outbreak is a disease or condition that occurs in greater-than-expected numbers. The departure from the norm can include the time of year during which the increase in illness appears, the specific group of people it affects, the geographical area it covers or the type of illness itself. For example, polio has become so rare in the U.S. that just a handful of cases in one area would be considered an outbreak. At the other end of the spectrum is the influenza virus. We have become so accustomed to the annual surge in influenza infections that, rather than calling it an outbreak, it is often referred to simply as “flu season.”

An outbreak that increases rapidly in both the number of new cases and in geographic scope is referred to as an epidemic. That’s what happened with COVID-19, which began as a localized outbreak in Wuhan and then spread throughout much of China. In this case, the epidemic was caused by a new strain of coronavirus that health officials believe “jumped” from animals to humans.

When an epidemic spreads across the globe, it’s known as a pandemic. The numbers of people who become ill, as well as the fatality rate, is much higher in a pandemic. Unfortunately, some news reports are misusing the word when talking about COVID-19. While it’s true that the virus has spread to other nations, the numbers of cases outside of China remain quite low at this time and don’t meet the definition of a pandemic.

A lot of people in the United States are worried about the new coronavirus, but the risk here is low. We agree with health officials who say that the greater health risk continues to come from our own ongoing influenza season. Respiratory viruses enter our bodies via the mucous membranes in the mouth, nose and eyes. So wash your hands often, don’t touch your face, and seek treatment and stay home if you’re sick. And remember, it’s still not too late for a flu shot.

(Send your questions to, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)