White Coat, Black Art·The Dose

Evidence suggests outdoor COVID-19 transmission is low. Here's what you need to know

The risk of catching coronavirus outdoors is very low, yet new pandemic restrictions in Ontario ban most outdoor sports and gatherings. Infectious diseases physician Dr. Sumon Chakrabarti joins Dr. Brian Goldman to debunk myths about outdoor transmission and explain why being outside is much safer than being inside.

Should you wear a mask outdoors? Experts weigh in

Crowds of people flock to a residential street in East Vancouver to enjoy the large cover of cherry blossom trees over the Easter long weekend. Experts say risk of coronavirus transmission outside is very low. (Gian Paolo Mendoza/CBC)

Amid rising COVID case counts, the messaging around being outside needs to change because the risk of outdoor transmission is "really, really small" and the health benefits of being outdoors are immense, said Dr. Sumon Chakrabarti, an infectious diseases physician at Mississauga Hospital.

Chakrabarti, who works in a COVID-19 hotspot, sees many patients with COVID — and they're not getting sick outside, he said.

Infectious diseases specialist Dr. Sumon Chakrabarti says the risk of coronavirus outside is "'really, really small.' (Dr. Sumon Chakrabarti)

"In the third wave, it is abundantly clear the people who are getting infected and sick enough to come in are those with heavy, prolonged indoor exposure," he told White Coat, Black Art and The Dose host Dr. Brian Goldman. "It's almost exclusively from high-density work settings or the family members thereof, or high-density living settings, such as shelters."

"This is part of the reason why I'm such a proponent of trying to mitigate risk and move things outdoors," he said.

Last week, Ontario banned many outdoor sports and activities, including soccer, tennis, basketball, golf and pickleball. Outdoor gatherings are also banned except for members of the same household or one other person from outside that household who lives alone. Some public health experts have raised questions about the restrictions.

People sit in Ottawa's Major's Hill Park April 10, 2021, the first weekend under that provincewide stay-at-home order. People are only allowed to spend time in person with people they live with or one other person who lives alone. (Rémi Authier/Radio-Canada)

The risk outside is much lower, according to Chakrabarti, because there is "essentially perfect ventilation," so any kind of aerosolized droplets containing the coronavirus disperse quickly and you aren't exposed to the same concentration of the virus.

That's why large crowds like the one in the downtown Toronto park Trinity Bellwoods last spring didn't result in a spike in COVID-19 cases, he said.

People wear face masks as they browse at an outdoor boutique in the Old Port in Montreal in early April. Some experts say face masks outside are mostly not necessary. (The Canadian Press)

A recent review of peer-reviewed papers found that evidence supports the belief that the risk of SARS-CoV-2 transmission is lower outdoors. However, the authors noted that while outdoor transmission is less common than indoors, it is not impossible and data is limited.

"The risk is not zero, but it's much better than being indoors," Chakrabarti told Goldman. 

Variants of concern 

Still, the more infectious coronavirus variants spreading across Canada are changing the risk of transmission outdoors, according to Benoit Barbeau, a virology expert at the Université du Quebec à Montréal.

"You'll probably need less virus to be exposed to in order to be infected ... which makes the variants a bit more transmissible outside."

However, Barbeau said if you follow public health guidelines outdoors, particularly keeping two metres apart, you should be protected. Indoors is a different story.

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Infectious disease expert Craig Jenne explains why coronavirus variants can spread more easily, even outdoors.

"What we know in terms of transmission being more aerosol-based than droplet based, [the variants] make it even more likely that if you don't apply the [distancing and masking] measures correctly indoors, you'll definitely be in a more dangerous situation." 

Barbeau said people should be encouraged to go outside whenever possible — and if indoors, "keep the airflow active, make sure you open windows and open doors."

Wearing masks outdoors 

While guidelines differ between provinces, some suggest wearing a mask, both indoors and outdoors, when physical distancing isn't possible.

Some countries, like France and Israel, have implemented mandatory masks outside at points in the pandemic. (Israel ended its outdoor mask mandate last week after a successful vaccination campaign.)

Despite this, Chakrabarti said masks aren't necessary in most situations outside.

"If you're going to be talking in relatively close quarters for a prolonged period of time, you could consider wearing a mask," he said.

Two friends speak to each other while physical distancing in Vancouver, B.C., on Monday, April 6, 2020. (Ben Nelms/CBC)

Barbeau said wear a mask if you feel more comfortable.

"But as a virologist, I think if you keep that two metre distance, I don't see a reason why you should wear a mask, variants or not."

Chakrabarti said a year into the pandemic, we can't "lock people in their houses or bubbles."

"We have to balance the risk mitigation for COVID, but also the risk of other things."

"Throughout the pandemic, we've had a really laser focus on COVID to the detriment of, I think, other types of illnesses. This is why I think being outdoors, getting some physical activity, being able to see your friends in a safe environment, these are all things that we need to be providing to people."

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