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Minnesotans are heading outside again. So how low are the risks for outdoor transmission of COVID-19?

When it comes to the chance of virus spread, not all outdoor gatherings are equal.

Fans watch from a grassy berm in right field prior to the spring training game between the Minnesota Twins and the Boston Red Sox in Fort Myers, Florida.
Fans watch from a grassy berm in right field prior to the spring training game between the Minnesota Twins and the Boston Red Sox in Fort Myers, Florida.
Jasen Vinlove-USA TODAY Sports

When the Minnesota Twins hold their home opener April 8, the team will have 10,000 people in the stands at Target Field in Minneapolis, making it the largest, or surely one of the largest, state-sanctioned gatherings since the COVID-19 pandemic began.

Other large outdoor venues, such as Minnesota United’s Allianz Field, will also be able to have big crowds starting April 1. Gov. Tim Walz has cited the state’s low rate of infection and the steadily increasing number of vaccinations as the reasons for allowing such events. But another factor is also key: They’re outdoors.

Which raises the question: As the weather gets warmer and more Minnesotans head outdoors, what does the science say about how safe it is to be outside? 

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Why outdoors is better

Early on in the pandemic, outdoor events were treated with extreme caution by health officials around the country. 

Professional and collegiate sports games were quickly canceled, returning later without fans. Health officials in Italy worried that a soccer match sparked the country’s spike in COVID-19 cases and a March 2020 game in Seattle drew criticism as a dangerous large gathering.  

In Minnesota, Walz kept parks open but initially closed campgrounds and golf courses. Attorney General Keith Ellison sued operators of a rodeo in Itasca County that allowed more than 250 people (many of whom eschewed masks and social distancing) to attend an event in July.

Gov. Tim Walz
REUTERS/Lucas Jackson
Gov. Tim Walz
Still, it was quickly apparent that being outdoors was safer, and over time the advantage of outside air and sunlight has become even clearer. Mass gatherings after police killed George Floyd in May didn’t appear to spike COVID-19 rates in Minnesota. And even though an infectious person attended the rodeo in Effie, the state didn’t report significant transmission due to the event. Research on the subject has found few cases that could be traced to outdoor transmission and few superspreader events outside.

Dr. Jill Foster, an infectious disease doctor and professor working for the University of Minnesota Medical School and M Health Fairview, said light aerosol droplets from a contagious person can float around indoors and infect people. But outdoors, they’re blown away, diluted and broken up by the rush of ever-moving air. “The air is constantly being exchanged with new air, there’s air currents all over the place,” Foster said.

Foster compared the virus particles to perfume. When someone sprays it indoors, people can smell it for a while — even if they leave the room. Outdoors, that smell gets dispersed far more quickly.

Potential examples of outdoor spread

Even if rare, transmission in outdoor settings or superpreader events is not impossible, health officials say. 

When MinnPost asked the Minnesota Department of Health if it had evidence of disease spread outdoors, agency officials said they found 31 COVID-19 cases tied to a July 4 concert at Stoney Point Recreation and Campground in Lincoln County, and confirmed 10 cases were from the same source.

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Agency spokesman John Schadl said there were 16 cases tied to a campaign rally for then-President Donald Trump in Bemidji last year, and four cases among protesters. Rally-goers were in a packed crowd for the Trump event.

While those events were held outside, Schadl said the state can’t be absolutely certain the actual transmission happened outside, rather than in indoor settings such as transit to the gathering.

State data show five outbreaks connected to concerts and three to festivals and fairs, activities that may have been outside. MDH says 167 people were potentially exposed to COVID-19 at block parties during the pandemic. When contact tracers investigate COVID-19 cases, they ask people about places they were potentially exposed 14 days before symptoms began. 

Kris Ehresmann
MinnPost photo by Peter Callaghan
Director Kris Ehresmann
“We’ve had some outdoor concerts and things like that in which … we did see a great deal of spread despite the fact that the activities were held outdoors,” said MDH Infectious Disease Director Kris Ehresmann. “I do think it’s important that while we celebrate the return of warmer weather and we take advantage of that for our socializing I think we want to be particularly careful to remember that while it’s better to be outdoors it’s not without risk.”

In Cook County, health officials traced a surge in COVID-19 cases back to a snowmobiling event on the Gunflint Trail held in late February. Cook County has reported 18 new COVID-19 cases in the last two weeks, and WTIP Radio reported Monday that health officials say there is more COVID-19 in the region than at any other point during the pandemic.

While the snowmobiling was, of course, outdoors, Grace Grinager, the public health supervisor for Cook County, said the event included stops “at a number of bars and restaurants.” (Though she wasn’t sure whether each location offered indoor or outdoor seating.)

“While it is impossible to know for certain where transmission occurred, we do know from a public health perspective that transmission from indoor gatherings at bars, restaurants, or in personal homes is more likely than transmission in an outdoor setting because of airflow,” Grinager said in an email.

When it comes to safety, not all outdoor gatherings are equal

Foster said not outdoor activities are the same. Outdoor activities where people are moving are generally safer. For instance, when people are going for a walk, “those aerosols don’t have a chance,” she said.

But things get a little riskier when people are stationary, especially for long periods of time. The more people involved, and the closer together people are, the more potential there is for spread. 

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At a baseball game, for instance, Foster said rows of people seated around each other for several hours who periodically scream and cheer isn’t great — even if it’s better than holding a party in your living room. (The Twins are generally trying to space people out throughout the stadium and closing off seats between groups.)

Foster also said people may travel to big events from other parts of the country with higher COVID-19 rates, also increasing risk.

Plus, in many cases, there are indoor gatherings tied to outdoor events. If you’re safe at your seat during a sports game, you still might spend time near others inside a bathroom or in transit on the way to the game.

Still, state data show hundreds of outbreaks since the pandemic began that were likely tied to indoor gatherings, such as restaurants, weddings, gyms and sports games, compared to the relatively small number of outdoor-related outbreaks MDH identified. Schadl said the state doesn’t get data to distinguish if an outbreak included outdoor seating such as a restaurant patio, though gatherings at those places in January and February were likely to be indoors.

“Being outdoors is absolutely better than being indoors when it comes to potential for transmission with COVID,” Ehresmann said.