Canada

Science suggests low risk of outdoor COVID-19 transmission. Here’s why

In an effort to stem the tide of COVID-19, a blanket ban on outdoor recreational activities in Canada’s largest province, Ontario, has raised some questions about outdoor transmission.

Under tightened new restrictions that went into effect Saturday, Ontario ordered the closure of outdoor sporting facilities, multi-use fields and portions of parks or recreational areas containing outdoor fitness equipment. Picnic sites and tables were also closed.

But experts argue that the risk of COVID-19 spreading outdoors when compared to indoor activities is much lower.

“You know, you’re taking away the safe options from people as you do nothing to impact the places where the disease is spreading at a time when our ICUs (intensive care units) are literally collapsing,” Dr. David Fisman, a professor at the University of Toronto and member of Ontario’s COVID-19 Science Advisory Table, said.

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With natural ventilation outside, the flow of fresh air can dilute and dissipate the virus particles, Jean-Paul Soucy, an infectious disease epidemiologist and PhD student at the University of Toronto, said. Fresh air can also evaporate the liquid droplets that carry the virus.

“The key here is ventilation,” said Soucy.

“Outside, you have perfect ventilation. Virus particles are rapidly dispersed.”

Additionally, the ultraviolet (UV) light from the sun can have a sterilizing effect, experts say.

“If permitting a dozen outdoor gatherings in a park averts just one indoor gathering, I think that trade-off is well worth it from a transmission risk perspective, not to mention the significant benefits to physical and mental health,” said Soucy.






Managing COVID-19 exposure risks while outdoors


Managing COVID-19 exposure risks while outdoors – Apr 11, 2021

In a previous interview with Global News, Dr. Zain Chagla, an infectious diseases physician at St. Joseph’s Healthcare in Hamilton, said outdoor transmission is “not that common and tends to be associated with close contact for a prolonged amount of time with others.”

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Several studies back that argument.

A systematic review of five peer-reviewed studies found that less than 10 per cent of the reported global COVID-19 cases had occurred outdoors.

The research also showed the likelihood of indoor transmission was nearly 19 times higher than outdoor spread.

Another peer-reviewed study from Italy published in the Environmental International journal indicated that the outdoor atmospheric concentrations of the coronavirus were very small.

Ontario’s new measures came amid record levels of coronavirus cases and hospitalizations that have ravaged the province during the third wave of the pandemic.

The province also closed all outdoor recreational amenities in March last year.

Read more:
With coronavirus variants spreading, are masks needed outdoors?

In addition to restricting outdoor gatherings to household members, a provincewide stay-at-home order was extended until at least May 20.

Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital, argued that outdoor activities are vital for mental and physical health, especially with stay-at-home orders still in effect.

“Ontario’s closure of outdoor recreational activities (including pickleball!) to control #COVID19 does not make sense,” he wrote on Twitter.

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“Science is clear: Outdoor COVID transmission is extremely rare.”

Other restrictions, including limiting capacity for in-person religious settings, funerals and weddings up to 10 people, went into effect on Monday.

Public health experts and epidemiologists have previously pointed to responsible outdoor recreation and gatherings as one of the last safe ways people can enjoy being in public settings during the pandemic.

“The biggest risk outdoors is if you’re in a face-to-face conversation with someone for a while unmasked,” Linsey Marr, professor of civil and environmental engineering at Virginia Tech, told Global News in a previous interview.

While recreational facilities, where you are constantly around other people, do present a “slightly higher risk” compared to other outdoor settings, having a mask on can minimize that, said Chagla.

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Bogoch also suggested that if physical distancing of two metres is not possible, people can wear a mask to keep protected.


Click to play video: 'COVID-19 crowding at popular outdoor areas'



COVID-19 crowding at popular outdoor areas


COVID-19 crowding at popular outdoor areas

Meanwhile, there is evidence that warmer weather seems to reduce the spread of COVID-19.

“We know it’s transmitted indoors in the workplace and in other gatherings and they largely turned a blind eye to much of that,” Andrew Morris, an infectious diseases specialist at Toronto’s Sinai Health and University Health Network, said.

After initially closing outdoor playgrounds, the provincial government backtracked over the weekend.

In a Tweet on Saturday, Premier Doug Ford said: “Ontario’s enhanced restrictions were always intended to stop large gatherings where spread can happen.”

“Our regulations will be amended to allow playgrounds but gatherings outside will still be enforced. Play outside safely. Parents keep your distance & wear masks if you can’t.”

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— With files from Global News’ David Lao, Katherine Ward



© 2021 Global News, a division of Corus Entertainment Inc.


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