In the absence of activity options since the implementation of the new containment measures, Montrealers are relying heavily on parks. But when there is an outdoor gathering, what are the real risks of the spread of COVID-19? Three experts give their opinion.
“Respiratory viruses are much less transmissible outdoors. When there is transmission of droplets and aerosols, the air will quickly dilute them and ensure that they do not remain concentrated in one place for too long, ”says Benoit Barbeau, virologist at the Department of Biological Sciences at the outset. UQAM.
This precept is also widely accepted within the scientific community. Studies even assess the risk of COVID-19 contagion to be 18 times lower outdoors than indoors.
Yet that doesn’t mean the risk of contagion is zero, warns Parisa Ariya, professor in the Department of Atmospheric and Oceanic Sciences and Chemistry at McGill University and an aerosol specialist. Studies show that an average of 10% of cases of COVID transmission occur outside, she emphasizes.
“Let’s be clear: the outward transmission exists. Unfortunately in Quebec, this risk of transmission has not been well explained ”.
Factors to consider
The distance that we keep from others also influences the risk of transmission, even outdoors, remind the experts.
Thus, the epidemiologist Dr. Nimâ Machouf and Mr. Barbeau recommend keeping a physical distance of two meters.
For her part, Ms. Ariya explains that aerosolized viruses can travel more than 7 m. However, the majority of large droplets and aerosols only travel a few meters. She therefore recommends keeping a physical distance of three or four meters.
Other important elements: time and frequency of exposure. Thus, passing a person for a moment offers a lower probability of transmission than if one speaks to a group of several people for an hour, illustrates Mr. Barbeau.
Physical activity would amplify in particular the force of transmission of aerosols and droplets. “Because people do cardio, they breathe very hard. At that point, the risk of droplet transmission is present, ”says Dr. Machouf.
Finally, meteorological factors would even have a role to play: cold air, denser than hot air, would be more conducive to the concentration of potentially infected particles, says Ms. Ariya.
“In winter, the dilution of bioaerosols is less effective. During the summer, there is better dilution, which decreases the transmission. The same goes for several droplets. “
Wear the mask or not outside?
As recommended by Quebec, Ms. Machouf and Mr. Barbeau maintain that outside, a physical distance of two meters or more would not require the wearing of a mask. However, wearing it “more aggressively reduces” the risk of contagion, tempers Mr. Barbeau.
For her part, Ms. Ariya advises instead to wear the mask outside at all times.
“You can lower it when there’s no one in sight, obviously. But when you see someone, when you cross them, you should put them on. “
|Since January 9, outdoor gatherings have been banned in Montreal.
Outdoor activities can only be done in the company of people from the same family circle, or another person for people living alone.
Wearing a mask is not mandatory in Quebec during outdoor activities, but is recommended when you are within two meters of a person who is not from our family bubble.
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– In collaboration with Laurent Lavoie