When it comes to infectious diseases in the news, you often hear terms like outbreak, epidemic, pandemic and endemic. The differences in these terms comes down to the scope of disease, the reach of people that could potentially be infected and how the illness spreads.
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Outbreak vs. Epidemic: Understanding the Scale
The difference between an outbreak and an epidemic is the scale at which populations are affected. Outbreaks are usually confined to a certain community, such as a school or town, whereas an epidemic affects a larger population like a state, entire region or country.
What is a disease outbreak?
A disease outbreak is defined by the Centers for Disease Control and Prevention, as an illness with a sudden rise in cases in a localized, geographic region. It is declared when there is a sudden, unexpected rise in the number of cases of an illness within a specific group — such as a school, neighborhood or hospital. While some outbreaks stem from a single source (like contaminated food) or a foodborne illness, others spread from person to person.
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What Is an Epidemic?
An epidemic is a rise in the number of cases of a disease beyond what is normally expected in a geographical area, according to the CDC. Frequently, the rise in cases happens quickly.
“It boils down to incidences and increases in certain areas,” says Dr. Manish Trivedi, an infectious disease doctor at AtlantiCare Regional Medical Center in Galloway, New Jersey.
For example, some areas may have a sudden spike in flu cases when the flu is prevalent. However, that increase in cases doesn’t spread among all countries and continents. It may not even spread across an entire state.
Epidemics happen frequently, but many people aren’t familiar with them unless they’re directly affecting their home region, Trivedi says.
Public health agencies continue to monitor multi-continent outbreaks, such as the 2025 to 2026 waves of highly pathogenic avian influenza (H5N1/Bird Flu) in poultry and livestock, to prevent them from scaling into wider human epidemics. A few examples of epidemics include the Mpox multi-country outbreaks of 2022 to 2024, the Zika virus outbreak (2016 to 2017), the West Africa Ebola outbreak (2014 to 2016) and the 2003 Severe Acute Respiratory System (SARS) outbreak in Asia. And most recently, the May 2026 Ebola outbreak in the Democratic Republic of the Congo. For an epidemic to stop, the number of cases needs to go down. This is often tied into stopping how it’s spread or transmitted.
[READ: Types of Respiratory Viral Infections.]
Epidemic vs. Pandemic: What Is the Difference?
The key difference between an epidemic and a pandemic is the scale at which the disease has spread. In an epidemic, the disease is spreading to a certain group or region at a rate faster than expected, whereas a pandemic is spreading across countries and continents.
What is a pandemic?
A pandemic is used to describe a disease that has spread across many countries and affects a large number of people. Neither the CDC nor the World Health Organization specify how many countries or how many people need to be affected in order for something to be declared a pandemic.
With a pandemic, everyone can be potentially exposed.
Key differences in scope and severity
Before a disease becomes a pandemic, it has to reach a few other levels, says Rodney Rohde, who is an honorary professor of international studies and associate director for the Translational Health Research Initiative at Texas State University in San Marcos, Texas.
Here are those levels, in increasing geographic reach:
— Sporadic. Used to describe when a disease is happening infrequently and irregularly
— Endemic. A disease or infection that’s a constant presence in a geographic area. For instance, there are tropical parts of the world where the mosquito-borne infection malaria is endemic.
— Epidemic. A sudden increase in the number of cases and is more than what’s expected for an area
— Pandemic. Widespread disease affecting multiple populations
Some previous examples of pandemics include:
— The Covid-19 pandemic. The pandemic was declared in 2020, and the WHO officially declared the end of COVID-19 as a public health emergency of international concern (PHEIC) in May 2023.
— The Spanish flu (H1N1 virus) of 1918. (Fans of the “Twilight” series may remember that Edward Cullen almost died during the Spanish influenza pandemic.) About 500 million people — a third of the population around the globe — were sick from the Spanish flu. A total of 50 million people or more died from it around the world, according to the CDC. The first people identified with it in the U.S. were military personnel.
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Historical and Modern Examples of Public Health Classifications
A pandemic may sound scarier than an epidemic, but it all depends on where you live. “A pandemic is more concerning for the world, but if you live where there is an epidemic going on, that’s just as concerning for you,” says Dr. Shira Doron, hospital epidemiologist at Tufts Medical Center and a professor of medicine at Tufts University in Boston.
You also may be concerned about both an epidemic and a pandemic if you live with a pre-existing condition or suppressed immune system, such as diabetes or COPD, that could make you more vulnerable to get a contagious infection.
Just like with an epidemic, a pandemic is over when the high number of cases diminishes. Making the decision to say that a pandemic is no longer present can be difficult. “I empathize with the WHO, CDC and others who are working during difficult times while trying to hit a constantly moving target,” Rohde says.
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What Does Endemic Mean? The Next Phase of a Virus
When a disease becomes endemic, it means the contagious disease is now a part of the general population. It means that the disease continues to spread, but at a predictable rate. For example, COVID-19 transitioned from a pandemic into an endemic phase in May 2023.
Summary of Differences: Epidemic, Pandemic and Endemic
Frequently Asked Questions (FAQ)
Is COVID-19 still considered a pandemic?
No, COVID-19 transitioned into the endemic phase in May 2023.
Can an endemic disease turn into an epidemic?
Yes, if there is a sudden spike in cases, beyond what is a baseline expectation of the disease spread.
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Epidemic vs. Pandemic vs. Endemic: What?s the Difference? originally appeared on usnews.com
