People wear face masks as they walk along a street in Montreal, Sunday, Oct. 18, 2020, as the COVID-19 pandemic continues in Canada and around the world. THE CANADIAN PRESS/Graham Hughes

People wear face masks as they walk along a street in Montreal, Sunday, Oct. 18, 2020, as the COVID-19 pandemic continues in Canada and around the world. THE CANADIAN PRESS/Graham Hughes

Canada updates COVID-19 guidelines to include airborne transmission, following U.S., WHO

New information was updated after top doctor recommended triple-layer masks

The Public Health Agency of Canada quietly updated its COVID-19 guidelines this week to include aerosol, or airborne, transmission of the virus.

The move came sometime late Tuesday (Nov. 3) or early Wednesday morning, within 24 hours of the country’s chief medical officer recommendation that masks should be triple-layered, including a filter.

READ MORE: Third layer’s the charm: Canada’s top doctor unveils new face mask recommendations

In a section within Canada’s COVID-19 online information hub titled “How COVID-19 spreads,” the modes of transmission have been updated.

“COVID-19 spreads from an infected person to others through respiratory droplets and aerosols created when an infected person coughs, sneezes, sings, shouts, or talks. The droplets vary in size from large droplets that fall to the ground rapidly (within seconds or minutes) near the infected person, to smaller droplets, sometimes called aerosols, which linger in the air under some circumstances,” the website reads.

The new statement does acknowledge that the “relative infectiousness of droplets of different sizes is not clear.”

The updated information cites outbreaks that occurred in settings with poor ventilation, with the agency said “suggest that infectious aerosols were suspended in the air and that people inhaled the virus.” Those settings include choir practice, fitness classes and restaurants.

“Transmission in these settings may have been facilitated by certain environmental conditions, such as re-circulated air,” the agency’s COVID-19 information reads.

“There is no evidence at this time that the virus is able to transmit over long distances through the air, for example, from room to room through air ducts. It is still unclear how easily the virus spreads through contact with surfaces or objects.”

The prior statements on COVID-19’s mode of transmission included only close contact, meaning “breathing in someone’s respiratory droplets after they cough, sneeze, laugh or sing,” as well as contaminated surfaces and common greetings such as hugs, handshakes and kisses.

Canada’s move came months after other public health agencies began to update their COVID-19 transmission guidelines.

In July, the World Health Organization (WHO) released data suggesting that airborne transmission can spread the novel coronavirus.

“Airborne transmission of the virus can occur in health care settings where specific medical procedures, called aerosol generating procedures, generate very small droplets called aerosols. Some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants or in fitness classes.”

In October, the U.S. Centre for Disease Control (US CDC) stated that “COVID-19 can sometimes be spread by airborne transmission,” citing situations where people more than six feet away from others still got infected with the virus.


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