Wednesday , May 31 2023

Modes of transmission of SARS-CoV-2: state of knowledge and use of indoor air ventilation systems


The National Institute of Public Health of Quebec (INSPQ) today publishes two reports on the state of scientific knowledge on the transmission of the SARS-Cov-2 virus and the role that indoor ventilation could play, especially in a pandemic context.

Literary review Transmission of SARS-CoV-2: findings and proposed terminology proposes to revise the definition of terms for the transmission of an infectious agent through the respiratory tract, favoring an approach based on a continuum of particle size.

Coughed by an infected person – symptomatic or not – who coughs, sneezes, laughs or speaks, the virus clings to particles of various sizes, ranging from drops larger than 100 µm – the thickness of a sheet of paper, to particles smaller than this size, called aerosols. The presence of SARS-CoV-2 was observed in particles of all sizes.

SARS-CoV-2 is transmitted mainly during close contact within 2 meters and prolonged (more than 15 minutes) between people. According to the proposed definitions, the available experimental and epidemiological data support aerosol transmission in the vicinity, ie at 2 meters. The literature also suggests that transmission can take place beyond 2 meters by aerosols, without, however, spreading over long-distance air, such as measles or tuberculosis.

Current scientific and epidemiological data remain limited, and the INSPQ continues to monitor the situation.

Keep your distance and ventilate

The INSPQ also looked at the viability of the virus in indoor environments and the use of ventilation to counteract transmission.

The scientific literature shows that the presence of SARS-CoV-2 virus is favored in the air at a temperature of 4 ° C and a relative humidity of 20 to 40%. The virus can survive in the air and on surfaces from minutes to hours, depending on the environmental contexts.

The risk of transmitting SARS-CoV-2 is increased indoors, inadequately ventilated, high occupant density and when exposure is prolonged.

The INSPQ recommends the preventive application of control measures in indoor spaces, considering that each building is unique and must be subject to a specific assessment. The use of ventilation should be recommended in conjunction with other protective measures, such as physical distance, minimization of contact and respiratory labeling.

The complementarity of all these control measures reduces the risk of COVID-19 transmission in indoor environments.

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