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A health-care worker talks with people as they wait outside a COVID-19 testing clinic in Montreal, on Jan. 3, 2021.

Graham Hughes/The Canadian Press

Canada needs to step up its efforts to limit the spread of COVID-19 through shared indoor air, a group of scientists and health care professionals is urging, as case counts soar across the country amid the emergence of a new, more contagious variant of the coronavirus.

In a letter released Monday, more than 500 signatories called on federal and provincial leaders to address the transmission of the virus through aerosols, tiny droplets that can linger in the air. There is greater urgency to do so as Canadians spend more time indoors during the winter, it said.

The group wants provincial leaders to mandate and fund assessments and upgrades of ventilation systems in public buildings, such as schools and long-term care homes, and develop ventilation standards for institutions and businesses such as restaurants, bars and gyms as part of reopening guidelines. It also urges them to ensure that high-risk health care and essential workers are not denied N95 or equivalent respirators.

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“The country, as a whole, and each province is not doing enough to acknowledge aerosol transmission of COVID-19 and promoting the appropriate measures to combat it,” such as ventilation and informing people about the risks of being in indoor spaces with multiple people, said Jennifer McDonald, a rehabilitation physician in Ottawa and one of the authors of the letter. Instead, she said, “we are continuing to focus on hand hygiene and two metres of distancing.”

How will the pandemic end? Not with a moment of triumph we’ll all remember, but with a slow whimper we’ll soon forget

Moreover, Dr. McDonald said, she and her fellow signatories, which include engineers, occupational health experts, infectious disease specialists and other health care professionals, believe aerosols play an important role in large COVID-19 outbreaks, such as those that have occurred in meatpacking plants, factories and long-term care homes.

“Many of these have very, very high attack-rate outbreaks, and we’re not seeing a big enough emphasis on the importance of ventilation and other strategies, including appropriately fitted masks,” she said.

How big a role aerosols play in the spread of COVID-19 is a contentious issue, with scientists debating how long the coronavirus can remain viable, how far it can spread and how much of it is needed to infect others when it is suspended in the air.

But in November, the Public Health Agency of Canada (PHAC) updated its information to include aerosols in its explanation of how COVID-19 spreads. It noted the disease is transmitted through respiratory droplets, which range in size from those that fall to the ground within seconds to aerosols that can remain in the air.

A September report from the Office of the Chief Science Advisor of Canada also offered advice for improving ventilation and indoor air quality to reduce transmission, including opening windows when possible, using portable air-filtration devices and mandatory ventilation management in public and crowded spaces.

Nevertheless, provincial health messaging does not yet adequately reflect this knowledge, Dr. McDonald said.

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While the signatories said physical distancing, masks and hand hygiene are still important, focusing on air quality would add another layer of defence, especially with a more transmissible variant of the virus, initially identified in Britain, now in Canada.

In an e-mailed statement, the B.C. Ministry of Health said there is no indication that the coronavirus is spread through airborne transmission.

“If the virus did spread through airborne transmission, the restrictions that we have in place that are stopping the spread of COVID-19, such as physical distancing, would not be working,” it said.

Meanwhile, in a report issued Dec. 1, Public Health Ontario said transmission of the virus over distances longer than two metres is less common but possible through prolonged exposure in poorly ventilated spaces. It explained that the term “airborne transmission” has a special meaning in public health, describing infections that efficiently spread through small particles suspended in the air. The dichotomy of airborne versus non-airborne pathogens is likely imprecise, it said, noting they can be considered on a spectrum.

In an e-mail, Public Health Ontario said it was reviewing the latest research on the use of portable air cleaners to improve indoor air quality in the context of COVID-19 and would likely release its review this week.

David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health and another of the letter’s signatories, likened the aerosol transmission of the coronavirus to cigarette smoke: installing plexiglass barriers does not prevent it from drifting to the other side.

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“You can’t combat something if you get the model wrong,” he said.

Signatory Brian Fleck, a professor of mechanical engineering at the University of Alberta, said the very small droplets created at the bottom of the lungs behave like a gas when expelled and move with the convection currents of the room. It is very well-established that viruses such as influenza, rhinoviruses and the SARS virus are transmitted this way,” he said.

Beyond the pandemic, investing in indoor air quality would reduce the spread of these viruses, help combat wildfire smoke and urban air pollution and improve the quality of life of people who suffer from allergies and asthma, he said.

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