Can Air Conditioning Spread COVID-19?

What to know about the AC units in your home, and air conditioning in your office, restaurant, gym, or other public spaces.

Many people have wondered if air conditioning can spread COVID-19, especially the AC in public places, like offices and restaurants.

Early research raised concerns. In the beginning months of the COVID-19 pandemic, a study published in July 2020 in Emerging Infectious Diseases found nine people in Wuhan, China, were infected with the virus simply by sitting near an air conditioning vent in a restaurant. According to researchers, the virus was spread by one asymptomatic diner who sat at a table in front of the AC unit. Four people at the table later tested positive for COVID-19, as did five people at neighboring tables.

Spread of COVID-19 in Indoor Spaces

Further studies explored the potential risks of exposure to COVID-19 in restaurants. A study published in February 2021 in the journal Physics of Fluid, looked at simulations of COVID-19 exposure in restaurants. Their data suggested a strong link between COVID-19 exposure and airflow patterns. They examined the issue of ventilation systems and air conditioning specifically. They explained how systems like air conditioning that recycle air, provide additional challenges and exposure to SARS-CoV-2 particles.

Manish Butte, PhD, an associate professor in the department of microbiology, immunology, and molecular genetics at the University of California, Los Angeles, told Health that within a public setting, like a restaurant, workplace, or gym, air conditioning might be potentially risky. It has to do with the way AC works. Air conditioning circulates air more rapidly, which removes humidity. Water vapor can hold onto heat, so with less of it in the air, a room or space cools down once the humidity is removed. "Less humidity in the air promotes evaporation, which causes droplets in the air to dry up and disappear," Butte said.

How Droplets Contribute to the Spread of COVID-19

It helps to understand a little about droplets. A study published in December 2021 in the journal International Communications in Heat and Mass Transfer discussed the role of droplets in the spread of COVID-19. Droplets contain mostly water but can also contain pathogens, such as SARS-CoV-2. According to the Centers for Disease Control (CDC), we spread droplets when we breathe, talk, cough, sneeze, and do other activities that involve exhaling. For example, a study published by the American Journal of Respiratory and Critical Care Medicine in September 2020, described how one cough can release 3,000 droplets, and a sneeze can release around 40,000 droplets.

According to the CDC, different actions produce different size droplets. In addition, these droplets travel varying distances. For example, when an AC unit is on, airflow from the vent pushes these droplets through the air and potentially into others. "The airflow direction is what matters," Butte said.

Erin Bromage, PhD, is a Comparative Immunologist and Professor of Biology at the University of Massachusetts Dartmouth. Erin wrote a blog post that went viral about how ventilation issues in indoor spaces with lots of people, such as crowded restaurants, caused concerns about COVID-19 transmission.

Butte agreed that air conditioning could make droplets containing infectious virus particles spread further. Remember, while air conditioning might make a room feel fresher on a warm day, it's recycled existing air.

Regarding the restaurant study in Wuhan, China, it's important to consider that it had a small sample size and didn't replicate conditions in a lab. "I don't necessarily think that this study is representative of transmission risk," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security in Maryland, told Health. "However, it is important to be mindful of airflow patterns, especially if they are strong and create a jet stream for droplets."

How To Reduce the Risk of COVID-19 in Spaces With Air Conditioning

So should we all be ditching our air conditioning systems until the threat of COVID-19 has passed? In a word, no. Air conditioning in your own home is far less risky than AC in a busy public place if you follow recommendations regarding hygiene. In addition, if you haven't had a stream of people in and out of your home, the only droplets that could be spread by air conditioning are those from you and whoever else is in your home. "Within a home, where everyone is highly exposed to each other, there isn't a need to worry about air conditioning," Butte said.

As for air-conditioned offices, malls, and restaurants, know that a risk exists, but most experts are not saying that you should refrain from venturing into public places. Spending time in any indoor space outside your home requires a certain level of risk assessment. If you go to a restaurant or any other busy place with air conditioning, following the CDC's guidelines will help prevent the spread of COVID-19. Guidelines may vary depending on where you are and likely involves measures such as social distancing, hand-washing, not touching your face, and, as always, staying home if you feel sick or have symptoms of COVID-19.

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.

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