With the United States' coronavirus epidemic resurging, Americans eager to reunite with their friends and families in a safe way are turning toward gathering outside. But some cities recently have linked coronavirus outbreaks to outdoor events, leaving some people to wonder: Are outdoor gatherings safe?

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Research suggests outdoor gatherings are safer than indoor events

According to Erin Bromage, a comparative immunologist and biology professor at the University of Massachusetts-Dartmouth, some research has shown that "[o]utside is definitely safer" than indoor gatherings when it comes to potentially transmitting or contracting the new coronavirus.

For example, the New York Times reports that, in a study that was released preprint and hasn't yet been peer-reviewed, researchers found that the chance of coronavirus transmission occurring indoors was nearly 20 times higher when compared with outdoors.

Further, in another preprint study that hasn't yet been peer-reviewed, researchers reviewed 7,000 coronavirus cases in China and found that just one of those cases stemmed from outdoor transmission, and the transmission likely occurred during a prolonged, face-to-face conversation.

Julian Tang, a virologist at the University of Leicester, explained that, generally, the more open a space, the less likely the novel coronavirus can become concentrated in one area in the air and then inhaled by another person, which can result in infection.

But outdoor gatherings still pose risks

But that doesn't mean that outdoor gatherings are without risk, experts say.

For instance, health officials in Rockland County, New York, recently found that nine cases of the novel coronavirus were connected to an outdoor gathering of 100 people. And in Washington, D.C., officials found that a backyard fundraiser with about 24 guests was linked to new cases of coronavirus infection among a few attendees.

Bromage explained that "the type of interactions you have when you're outside" are "important."

"I think people hear that it's outdoors and think everything is fine," said Linsey Marr, an engineering professor and aerosol scientist at Virginia Tech. However, she said, "If you have an outdoor gathering with a lot of people talking, you stand close. It's loud, so you talk louder," and that can increase risk of transmission.

Asaf Bitton, executive director of Ariadne Labs at Brigham and Women's Hospital and the Harvard T.H. Chan School of Public Health, said large gatherings make it difficult to maintain the physical distance needed to protect yourself from potential transmission, even if the event is held outdoors. In addition, inviting more people increases the possibility that someone at the gathering is infected and could transmit the virus, Bitton said.

"Spewing respiratory droplets over a longer distance can occur [outdoors] if someone has a vigorous cough," Krysia Lindan, a clinical epidemiologist at the University of California-San Francisco, noted.

Consuming alcohol at an outdoor event also could be risky, according to Bitton. He noted that alcohol "can significantly alter all senses" and make it even more difficult for people to maintain appropriate physical distance.

"One of the problems that happens with parties or events like this if alcohol is involved, even the most well-meaning individual who is trying to stay apart a certain number of feet, it's an unnatural act," Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy, explained. "People do come together. That's just human nature."

How can you keep outdoor gatherings safe?

Still, there are steps you can take to gather with friends and extended family outdoors while keeping your risk of coronavirus transmission low.

Marr said people gathering outdoors should remember that they should keep physical distance between them and anyone who doesn't live in their household. "It should be outdoors with distancing."

While health experts largely recommended keeping at least six feet of distance between yourself and people who don't live in your household, Joseph Allen, director of the Healthy Buildings program at the Harvard T.H. Chan School of Public Health, said, "10 feet is better."

Experts also suggested not hosting or attending outdoor events where alcohol is served and bringing your own or asking guests to bring their own food, drinks, and dish wear to outdoor gatherings. In addition, some experts recommend that you wear a mask when in close conversation with others, even when outdoors, and that you only gather with others who are practicing physical distancing and other precautions to protect themselves from the coronavirus.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said "on the rare occasion" that he and his family "have people over, we have them out on the deck, six feet apart, and we never have more than two people, and they are people who themselves are" practicing social distancing. He added, "We wear masks, unless we are eating. We don't share anything. There are no common bowls. Each person has his or her own receptacle. Some people even bring their own glasses. We always do takeout and I tell the takeout people that I want the food in four separate plastic containers, so no one has to touch anyone else's food."

Elizabeth Connick, chief of the infectious diseases division and a professor of medicine and immunobiology at the University of Arizona, said she's "had a few people over to dinner and [they] eat outside." She explained, "I don't have many people over. The people I have over have been quarantining. We don't wear masks. We sit outside at a good distance. I think if you are outside at a good distance the risk is very small. I invite over people who are very circumspect in their behavior. No one comes over to my house who goes to restaurants or bars."

You also should keep your community's infection rate in mind when determining whether to host or attend an outdoor gathering, because as your area's infection rate increases, so does your risk of coming into contact with someone who's infected with the novel coronavirus.

According to the Times, people should avoid socializing with anyone who doesn't live in their household when the positivity rate for coronavirus tests in their areas exceeds 5%.

However, Lindan said the resurgence of America's coronavirus epidemic over the past couple weeks has gotten to a level at which "no one should be out without a mask, and everyone should be trying to distance as much as feasible, even if retail (and other businesses) are opening up."

Overall, Lindan explained, "Nothing has changed about precautions to prevent yourself and others from becoming infected." She said, "Wear a mask at all times that you are out … which ideally would occur at least six feet away from others in your 'safe' group. Clean/disinfect your hands," and "[b]eing outside for activities, for seeing friends, and for eating is better than inside" (Parker-Pope, New York Times, 7/3; Courage, Vox, 7/11; Reddy, Wall Street Journal, 6/15; Cimons, Washington Post, 7/3).