What Is a Syndemic?

The spread of COVID-19 has given us no shortage of public health lingo to work into our daily vocabulary. You probably have at least some understanding of what pandemic, endemic, and epidemic mean. Now there's a new word to know: syndemic.

What Is a Syndemic, Exactly?

If you haven't heard this term before, you're not out of the loop. A syndemic is "more of a term of art" vs. something that public health experts use regularly, said infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security.

Still, there is an official definition out there. The Centers for Disease Control and Prevention (CDC) defines syndemics simply as "synergistically interacting epidemics," meaning they are what happens when two epidemics—higher-than-normal levels of an illness in a community—occur at the same time.

It's a term that was used to describe what happened in Maine in April 2021. The state saw an increase in COVID-19 cases while residents were being vaccinated against the virus. The Maine Center for Disease Control and Prevention Director Nirav Shah, MD, used the term in a press briefing to describe what the state was experiencing. Dr. Shah described a syndemic as "two parallel occurring epidemics that are unfolding in the same real-time together that may or may not have interconnections with one another."

Maine had reports of 30 cases of alpha, or B.1.1.7, the COVID-19 strain that was first discovered in the United Kingdom in September 2020, along with three cases of beta, or B.1.351, the variant first detected in South Africa in May 2020, and one case of gamma, or P.1, the variant first detected in Brazil in November 2020. In Dr. Shah's opinion, this sort of syndemic phenomenon coupled with variants that were more contagious than previous ones could have been what was causing the state's increasing case numbers.

Syndemic vs. Pandemic vs. Epidemic?

The premise behind a syndemic is that pandemics and epidemics wouldn't occur without the presence of certain social and health conditions in a community, according to a 2021 study published in ScienceDirect. A syndemic happens when multiple pandemics or epidemics are present simultaneously.

To keep the terms in order, here are a few CDC definitions:

• Comorbidity means that there is more than one disease or condition present in the same person at the same time.
• An epidemic happens when there is a higher level of illness or health condition than is expected in a community or region.
• A pandemic is an epidemic that happens worldwide or over a very wide area and usually impacts a large number of people.
• An endemic happens when a condition is continuously present in a location or population.

There can be some overlap here, said Dr. Adalja. "You could say that diabetes and COVID-19, or obesity and COVID-19 are syndemics," explained Dr. Adalja, since obesity is considered an epidemic or pandemic and, of course, COVID-19 is a pandemic. "But they can also be comorbidities," added Dr. Adalja, meaning they can occur at the same time in the same person.

It's important to keep in mind that a syndemic does not have to be limited to only diseases and medical conditions.

One example of a pre-COVID-19 syndemic in medical literature was published in 2019 in The Lancet. The commission report looked at something called "The Global Syndemic," which researchers explained as three pandemics—obesity, undernutrition or malnutrition, and climate change—that affect people worldwide. According to the report's authors, these three issues "constitute a syndemic, or synergy of epidemics, because they co-occur in time and place, interact with each other to produce complex sequelae, and share common underlying societal drivers." Sequelae are what medical professionals refer to as conditions that occur as a result of a previous disease or injury.

"The Global Syndemic" was brought on by two diseases or health conditions—obesity and undernutrition—as well as environmental and social factors (climate change). And there can also be a syndemic of pandemics or epidemics, like the flu and COVID-19. "It's just two parallel disease processes," said Dr. Adalja.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.