Risk of outdoor COVID-19 transmission is higher in the winter

As Ontario continues to see surging levels of COVID-19 transmission, one epidemiologist is raising concerns that outdoor activities may not be the safe refuge from the virus that they were in the summer.

Colin Furness, who is a professor at the University of Toronto, tells CP24 that while being outside continues to be “much better” than being indoors it is a “little less safe” than it was in the summer due to the way virus behave in colder, drier air.

He says that when the air is hot and humid droplets” get heavier not lighter and they sink to the ground,” meaning that you would have to be extremely close to someone with COVID-19 to be exposed to the virus.

But he says that when the temperature drops and the air gets drier the droplets tend to remain airborne for longer periods of time.

He says that the mucus membranes in our nose, mouth and throats also dry out in colder weather “and don’t work nearly as well at filtering out the pathogens.”

“There is a good reason why we have flu season and cold season in the winter. In cold, dry air when the virus leaves your mouth when you exhale it doesn’t start to die right away like it does in hot weather; it stays very much alive,” he said. “In cold, dry weather when you exhale and you can see your breath you are seeing those droplets and the droplets disappear in an instance, meaning the water evaporates so those very live virus particles are floating in the air.”

Public health officials and epidemiologists have long said that individuals are at a greater risk of contracting COVID-19 when indoors and the province has largely taken this into account, choosing to first allow patio service to reopen in the summer before also allowing indoor dining.

Speaking with CP24, Furness said that being outside still offers benefits because the breeze can help to blow droplets away compared to indoor settings where the air is ‘recycled.”

But he said that people should nonetheless be aware of the fact that the virus “behaves very differently in the winter” and take precautions to avoid crowd scenes when they are out and about.

“Shared air without masks is what makes people sick,” he said.

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