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COVID-19: introduction, transmission and prevention
COVID-19 (update 2020-11-06)
The COVID-19 virus is a coronavirus (its name derives from the fact that the virus has a crowned appearance), which is part of the betacoronavirus family; there are several types of coronavirus and several forms can be pathogenic to humans. COVID-19 is the same subtype as SARS (Severe Acute Respiratory Syndrome). The designated name in the medical literature is SARS-CoV-2.
How is the SARS-CoV-2 virus actually transmitted?
The COVID-19 virus is spread primarily through transmission through infected droplets. The virus can also stay suspended in smaller particles, aerosols. It can also be transmitted by contact with contaminated surfaces (by subsequent contact of contaminated hands with the nose, eyes or mouth, for example).
The simple act of speaking releases particles continuously. The activities of breathing, talking or coughing, among others, can produce particles of different sizes, ranging from aerosols smaller than 1 micron (µm) to much larger droplets. Traditionally, droplets are 5 µm or more in size and aerosols are less than 5 µm in size, but some nuances exist. Droplets tend to fall on surfaces within a radius of about 2 meters, while aerosols can remain suspended in the air for some time.
For a virus to be a source of infection transmitted through the respiratory tract (via the nose, mouth, throat, bronchial tubes, lungs), it must meet certain criteria. First, the viral load must be high enough, that is, there are enough viral particles. Next, the virus must have the ability to infect a host cell in the human body (infectivity). Then, the virus must have specificity for a particular cell or tissue (tropism). In addition, environmental factors must promote the survival and growth of the virus.
In the case of SARS-CoV-2, its main gateway is the nose, which contains a large number of receptors for this type of virus. The virus has the highest activity level, therefore, in the nose, with a concentration that decreases as the virus moves through the airways. In comparison, other types of coronavirus cause a good proportion of cases of common colds.
Preventive measures for transmission: what works? What type of mask should I wear?
By maintaining good hygiene practices, it is possible to reduce the risk of transmitting SARS-CoV-2. The two-meter separation between people allows larger particles, droplets, to fall on surfaces and reduce the risk of airborne transmission. Wearing an appropriate protective mask reduces the risk of droplets and aerosols being released into the environment, and therefore helps protect others while protecting yourself. Proper hand hygiene helps reduce transmission by reducing the chances of the virus surviving on the hands, which can be important vectors.
Since the start of the pandemic, several studies have been carried out on the optimal methods of protection. Although there are still some uncertainties, it is generally recommended to follow updated guidelines from Public Health.
In health care settings, such as hospitals and medical clinics, certain other recommendations apply, such as wearing a procedural mask (not a face covering or craft mask) in areas where community transmission is higher. This is particularly important since procedural masks are more effective against respiratory transmission when this occurs through both droplets and aerosols, as is the case with SARS-CoV-2.
This is why many healthcare settings will require their professionals, employees, patients and caregivers to wear this type of mask.
In addition, since the number of people who can be present in an enclosed space is limited, it is recommended that patients come without an accompanying person to receive care or services, with some exceptions (for children or people requiring assistance, for example) .
Outside of healthcare settings, wearing an appropriate procedural or non-medical mask remains an important recommendation. For up-to-date information on the types of masks recommended, we suggest that you consult the websites of the Government of Canada, the Government of Quebec or the Institut national de Santé publique du Québec (INSPQ).
Sources et références
• Zhang, Sophie et Caroline Duchaine, SARS-CoV-2 and Health Care Worker Protection in Low-Risk Settings: a Review of Modes of Transmission and a Novel Airborne Model Involving Inhalable Particles, Clinical Microbiology Reviews, Janvier 2021, volume 34, issue 1, e00184-20.
• UpToDate, Coronaviruses, mise à jour juin 2020.
• UpToDate, Coronavirus disease 2019 (COVID-19): Epidemiology, virology, and prevention, mise à jour octobre 2020.
• UpToDate, Coronavirus disease 2019 (COVID-19): Clinical features, mise à jour octobre 2020.
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