What’s the difference between a pandemic, an epidemic, endemic, and an outbreak?
Discussed and Amended
Robert Gorter, MD, PhD.
July 1st, 2020
Not all infectious disease terms are created equal, though often they’re mistakenly used interchangeably. The distinction between the words “pandemic,” “epidemic” and “endemic” is regularly blurred, even by medical experts. This is because the definition of each term is fluid and changes as diseases become more or less prevalent over time.
While conversational use of these words might not require precise definitions, knowing the difference is important to help you better understand public health news and appropriate public health responses.
Let’s start with basic definitions:
AN EPIDEMIC is a disease that affects a large number of people within a community, population, or region.
A PANDEMIC is an epidemic that’s spread over multiple countries or continents.
ENDEMIC is something that belongs to a particular people or country.
AN OUTBREAK is a greater-than-anticipated increase in the number of endemic cases. It can also be a single case in a new area. If it’s not quickly controlled, an outbreak can become an epidemic.
Epidemic vs. Pandemic
A simple way to know the difference between an epidemic and a pandemic is to remember the “P” in the pandemic, which means a pandemic, has a passport. A pandemic is an epidemic that travels.
Epidemic vs. Endemic
But what’s the difference between an epidemic and endemic? An epidemic is actively spreading; new cases of the disease substantially exceed what is expected. More broadly, it’s used to describe any problem that’s out of control, such as “the opioid epidemic.” An epidemic is often localized to a region, but the number of those infected in that region is significantly higher than normal. For example, when COVID-19 was limited to Wuhan, China, it was an epidemic. The geographical spread turned it into a pandemic.
Endemics, on the other hand, are a constant presence in a specific location. Malaria is endemic to parts of Africa. Ice is endemic to Antarctica.
Endemic vs. Outbreak
Going one step farther, an endemic can lead to an outbreak, and an outbreak can happen anywhere. Last summer’s dengue fever outbreak in Hawaii is an example. Dengue fever is endemic to certain regions of Africa, Central and South America, and the Caribbean. Mosquitoes in these areas carry dengue fever and transmit it from person to person. But in 2019 there was an outbreak of dengue fever in Hawaii, where the disease is not endemic. It’s believed an infected person visited the Big Island and was bitten by mosquitoes there. The insects then transferred the disease to other individuals they bit, which created an outbreak.
You can see why it’s so easy to confuse these terms. They are all related to one another and there is a natural ebb and flow between them as treatments become available and measures for control are put in place — or as flare-ups occur and disease begins to spread or die out.
Theoretically and per definition; in how far is a pandemic different?
- Affects a wider geographical area, often worldwide (most flu epidemics are therefore actually pandemics)
- Infects a larger number of people
- Often but not necessarily, caused by a new virus or a new strain of the virus that has not circulated within people for a long time
- Humans have little to no immunity against the virus and it spreads quickly
- Causes more deaths
- Often creates social disruption and economic loss
The terms pandemic and epidemic are never used to indicate the severity of the disease, only the degree at which the disease is spreading.
Why declare a pandemic?
Declaring a pandemic allows national and global public health agencies to respond to the situation at a much higher degree and with more mandates. For instance, a lockdown and upholding democratic principles like Freedom of Speech or Freedom of Movement can only be executed when an epidemic has been declared a pandemic.