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Notre résumé de recherche sur la COVID-19

Le document suivant (en anglais) se veut un aperçu des données scientifiques à ce jour en relation au COVID-19, ainsi qu’une mise à jour des directives internationales sur la prévention et le contrôle des infections liées au COVID-19. Il ne prétend pas être une liste complète de toutes les données de recherche disponibles. Notre compréhension du COVID-19 évolue quotidiennement selon les données scientifiques émergentes.

Ce document de recherche vous est offert à titre d’information. La FCSII ne peut garantir l’exactitude et l’intégralité de l’information car la FCSII n’a pas participé à la révision ou à la production de ces données.

How does COVID-19 spread?

The U.S. Centers for Disease Control and Prevention states under ‘Modes of Transmission’: “The virus is thought to spread mainly from person-to-person: Between people who are in close contact with one another (within about 6 feet); through respiratory droplets produced when an infected person coughs or sneezes. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.”

The World Health Organization’s recently published Risk Communication Package for Healthcare Facilities for COVID-19 says that COVID-19 spreads most easily: “[…] through close contact with an infected person. When someone who has COVID-19 coughs or sneezes, small droplets [aerosols] are released and, if you are too close, you can breathe in the virus.”

From The Online Citizen: Medical experts from China and S. Korea underline importance of wearing mask during COVID-19 pandemic – contrary to WHO’s recommendation, March 30, 2020. The article includes the following comments by Dr. Kim Woo-joo, a professor of infectious diseases at the Korea University Guro Hospital and South Korea’s most prominent coronavirus expert:

“Citing the Shincheonji church gathering in late Feb — which led to a supercluster in the city of Daegu and an astronomical spike in cases nationwide — Professor Kim said: “Imagine these hundreds of people gathered within one to two metres of each other, praying and singing for hours … If one infected person is present, think about the number of droplets produced.”

“We all spit even when we talk normally. but if you are singing and shouting, you are going to get a lot of droplets. Gravity doesn’t pull all the spit down, which means the droplets don’t land within one to two metres … because the air can also flow sideways,” said Professor Kim, adding that the droplets can travel “much further” than the said distance.

The droplets shrink to less than 5 microns when they dry out, turning into an aerosol that allows them to travel as far as two metres, he said.

That’s how a person standing quite a few feet away can still get infected,” said Professor Kim.”

Via NPR: WHO Reviews ‘Current’ Evidence on Coronavirus Transmission Through the Air, March 28, 2020. The article includes an interview with Dr. Donald Milton, an infectious disease aerobiologist at the University of Maryland’s School of Public Health.

[Dr. Milton] says people like to think that there’s some sharp, black-and-white distinction between “airborne” viruses that can linger and float in the air and ones that spread only when embedded in larger moist droplets picked up through close contact, but the reality of transmission is far more nuanced.

“The epidemiologists say if it’s ‘close contact,’ then it’s not airborne. That’s baloney,” he says.


In the face of this uncertainty, Milton thinks the WHO should follow the example of the CDC and “employ the precautionary principle to recommend airborne precautions.” 


“I think the WHO is being irresponsible in giving out that information. This misinformation is dangerous,” says [Milton].

According to the following study: Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center, Santarpia, J.L. et al., March 23, 2020

“SARS-CoV-2 is shed during respiration, toileting, and fomite contact, indicating that infection may occur in both direct and indirect contact.”

In a recent comprehensive review of the literature (March 19, 2020) commissioned by the National Union of Public and General Employees (NUPGE) on the modes of transmission for COVID-19 (and efficacy of surgical masks versus N95s as respiratory protection), Dr. John H Murphy, Adjunct Professor of Dalla Lana School of Public Health, University of Toronto, and President of Resource Environmental Associates Limited, notes that public health agencies in Canada have stated that the virus is not known to be airborne (e.g., transmitted through the particles floating in the air), but that this is only because aerosol transmission of COVID-19 has not yet been studied.

“Many public health authorities persist in discounting aerosol transmission while ascribing to theories of droplet and contact as dominant modes of transmission, despite the existence of comparatively little scientific support.”

Noting that “the science strongly points to the likelihood of aerosol transmission of influenza and coronaviruses as a significant mode of person-to-person infection”, he concludes: “[…] thus far, COVID‑19 is not known to be expelled from patients, nor transmitted in the atmosphere, nor to induce respiratory infection in ways that markedly differ from seasonal influenza or coronaviruses.”

“In other words, for COVID-19, we have neither specific positive nor negative evidence with respect to modes of transmission, but we have substantial evidence in respect of the influenza and coronaviruses responsible for several global and regional outbreaks over the past twenty years.”

Noting that “severe cases that necessitate hospitalization are due to pneumonia, and that COVID-19 also infects tissues in the mid-airway”, Dr. Murphy states, “It is therefore reasonable to conclude that patients with pneumonia are likely to exhale respirable droplets (i.e. those under 10 microns in aerodynamic diameter) containing viruses during ordinary and assisted breathing, and that productive coughing may also expel larger visible droplets (i.e. 50 microns and larger) containing viruses.”

Similarly, Dr. Lisa Brosseau, a U.S. national expert on respiratory protection and infectious diseases and Professor Emerita at University of Illinois in a commentary for the Center for Infectious Disease Research and Policy (March 16, 2020) questions the experts who call for droplet and contact precautions only for health care workers, saying that, in offering this guidance, experts are failing to recognize the potential for inhalation of small airborne particles very close to the infectious source:

“Based on research now more than 70 years out of date, the infection control paradigm of contact, droplet, and airborne transmission fails to recognize inhalation of small airborne particles very close to an infectious source – ie, within 6 feet.”

“Talking, breathing, coughing, and sneezing create an aerosol (a suspension of particles in the air) containing particles in a range of sizes, with viable infectious organisms present in both small and large particles. Contrary to popular belief, the larger particles (5 to 15 micrometers [µm]) will not immediately drop to the ground but will remain airborne for several minutes. Smaller particles (less than 5 µm) will remain in the air for many minutes or even hours. All particles will immediately begin to evaporate (mucus contains a lot of water), which means the range of particle sizes will decrease overall. Smaller particles are more affected by diffusion than gravity, thus making them more likely to remain airborne. In the absence of air currents, airborne particles will disperse slowly throughout a space. Higher doses of infectious particles are more likely to result in infection and disease.” Brosseau cites a very recent study found that “SARS-CoV-2 aerosols remain viable for up to three hours, which is similar to the viability of SARS-CoV-1 in air and MERS-CoV… adequate time for exposure, inhalation, and infection to occur both near and far from a source.”

Brosseau notes in China, after health care workers contracted the virus, “patients with critical or severe symptoms were moved into designated wards or hospitals while those with mild symptoms were cohorted in temporary hospitals in repurposed buildings.” In these facilities, “healthcare workers wore full protection, including a gown, head-covering, N95 filtering facepiece respirators, eye protection, and gloves.”

In this March 10, 2020 interview, CIDRAP Director Michael Osterholm describes COVID-19 as an “airbone virus”.

From Wired Magazine: “They Say Coronavirus Isn’t Airborne – but It’s Definitely Borne By Air”, March 14, 2020:

“When you breathe out or cough, you release bits of watery mucus from inside your body in a wide array of sizes, ranging from bigger, wetter ones to finer ones. All of these are droplets. The smallest droplets are commonly described as aerosols. Whatever you call them, though, any of these bits of mucus may be laced with viral pathogens.”

Multiple modes of transmission of infectious agents

In a 2009 paper titled Relative contributions of four exposure pathways to influenza infection risk by Dr. Mark Nicas and Dr. Rachael Jones, the authors argue that we need to reframe the problem of transmission to assume that all infectious agents can theoretically be transmitted along all pathways. In the early stages of an outbreak, when there remains significant uncertainty as to what proportion of transmission follows each path, governments should protect health care workers by assuming the possibility of all paths of transmission and act accordingly in terms of mandating the appropriate personal protective equipment for all health care workers at risk.

From Science Daily: “New Studies Suggest Airborne SARS Transmission is Possible”, April 6, 2005

“Two new studies present evidence that the virus causing severe acute respiratory syndrome (SARS) may spread through the air, not just through direct contact with contaminated water droplets as previous research had shown.”

What about asymptomatic transmission?

From The Lancet: COVID-19 in children: the link in the transmission chain, March 25, 2020

“The most important finding to come from the present analysis is the clear evidence that children are susceptible to SARS-CoV-2 infection, but frequently do not have notable disease, raising the possibility that children could be facilitators of viral transmission.”

From the Journal of Emerging Infectious Diseases: Serial interval of COVID-19 among publicly reported confirmed cases

“12.6% of case reports indicated presymptomatic transmission.”

Are surgical masks – designed for droplet and contact precautions – adequate respiratory protection in light of what we are learning about COVID-19?

From the New York Times: “How Long Will Coronavirus Live on Surfaces or in the Air Around You?”, March 17, 2020

“Dr. Linsey Marr [an expert in the transmission of viruses by aerosol at Virginia Tech] said the World Health Organization has so far referred to the virus as not airborne, but that health care workers should wear gear, including respirator masks, assuming that it is.

“Based on aerosol science and recent findings on flu virus,” she said, “surgical masks are probably insufficient.”

From Live Science, “Specialized respirators are key to stopping spread of coronavirus to medical staff”, February 20, 2020

“About 280 medical staff in the hospital’s Respiratory, ICU and Infectious Diseases departments wore N95 respirators and washed their hands frequently, while about 215 in the departments of Hepatobiliary Pancreatic Surgery, Trauma and Microsurgery, and Urology wore no masks and disinfected their hands less frequently. Although the respirator group encountered confirmed cases more often than the unmasked group — more than 730% more often — no one in the respirator group became infected. In comparison, 10 people in the unmasked group contracted the novel disease, despite treating fewer infected patients.”

A recent (dated February 13, 2020) Lancet article on COVID-19 outbreak calls for “aggressive” measures (N‑95 masks, goggles and protective gowns) to ensure the safety of health care workers treating suspected or confirmed cases of COVID-19.

From a 2017 study:The efficacy of medical masks and respirators against respiratory infection in healthcare workers (a randomized control trial of 3,591 subjects comparing medical masks and respirators)

“The results suggest that the classification of infections into droplet versus airborne transmission is an oversimplification. Most guidelines recommend masks for infections spread by droplets. N95 respirators, as “airborne precautions,” provide superior protection for droplet‐transmitted infections. To ensure the occupational health and safety of healthcare worker, the superiority of respirators in preventing respiratory infections should be reflected in infection control guidelines.”

From the 2014 World Health Organization Guidelines: Infection prevention and control of epidemic- and pandemic-prone acute respiratory infections in health care

“When a new infectious disease is identified, the modes of transmission are not well understood. The epidemiological and microbiological studies needed to determine the modes of transmission and identify possible IPC measures may be protracted. Due to the lack of information on modes of spread, Airborne and Contact Precautions, as well as eye protection, should be added to the routine Standard Precautions whenever possible, to reduce the risk of transmission of a newly emerging agent (Annex B describes Standard and other precautions). These precautions should be implemented until further studies reveal the mode of transmission.”

From the Institute of Medicine, on the role of surgical masks (2010):

“Face masks, including surgical and procedure masks, are loose-fitting coverings of the nose and mouth that are designed to protect the patient from secretions from the nose or mouth of the physician, nurse, or other healthcare professional. Face masks are not designed or certified to protect the wearer from exposure to respiratory hazards.”

From the Council of the Canadian Academies: Efficacy of surgical masks compared to N-95 respirators, December 2007

“In 2007, the Public Health Agency of Canada asked the CCA to assess the modes of transmission of influenza and the contribution of respirators or surgical masks in inhibiting the spread of the virus. The Expert Panel on Influenza and Personal Protective Respiratory Equipment concluded that the current weight of evidence shows that transmission of influenza by inhalation is MORE probable than by direct contact. The Panel also found that N95 respirators do protect against the inhalation of many types of particles while surgical masks worn by an infected person can also play a role in transmission prevention.“

From the Ontario SARS Commission Inquiry: Final Report (2006)

A recent study by the Institute of Medicine of the National Academies, whose authors included Dr. Allison McGeer of Toronto’s Mount Sinai Hospital, said:

“The loose fit of most medical masks [i.e., surgical and procedure masks] leaves gaps that could allow substantial contaminant leakage into and from the mask … Medical masks may be used as barriers against disease transmission by fluids, especially blood, and some large droplets, and they are designed to prevent release to the environment of large droplets generated by the wearer. They are not designed or approved for purpose of protecting the wearer against entry of infectious aerosolized particles potentially surrounding the wearer and his mask.”

What are other countries doing to protect health care workers from COVID-19?

U.S. Centers for Disease Control and Prevention (CDC)

Interim Infection Prevention and Control Recommendations for Patients with Confirmed Coronavirus Disease 2019 (COVID-19) or Persons Under Investigation for COVID-19 in Healthcare Settings (updated March 10, 2020)

Swabbing: N95 respirator recommended as collecting diagnostic respiratory specimens (e.g., nasopharyngeal swab) is likely to induce cough or sneezing.

According to the CDC:

“Use of N95 or higher-level respirators are recommended for HCP who have been medically cleared, trained, and fit-tested, in the context of a facility’s respiratory protection program.” 

The above applies if the supply chain is able to meet the demand.

In addition, the CDC’s updated PPE recommendations stipulate that:

  • Facemasks protect the wearer from splashes and sprays.
  • Respirators, which filter inspired air, offer respiratory protection.

European Centre for Disease Prevention and Control

From the Infection prevention and control for COVID-19 in healthcare settings (March 2020)


“Healthcare workers performing aerosol-generating procedures (AGP), such as swabbing, should wear the suggested PPE set for droplet, contact and airborne transmission (gloves, goggles, gown and FFP2/FFP3 respirator).”

Confirmed or suspected case:

“Healthcare workers in contact with a confirmed case, or a suspected case of COVID-19, should wear PPE for contact, droplet and airborne transmission of pathogens: FFP2 or FFP3 respirator tested for fitting, eye protection (i.e. goggles or face shield), long-sleeved water-resistant gown and gloves.”

Triage, initial contact and assessment:

“If there is a shortage of FFP2/FFP3 respirators, healthcare workers performing procedures in direct contact with a suspected or confirmed case (but not at risk for generating aerosol) can consider wearing a mask with the highest available filter level, such as a surgical mask, in addition to gloves, goggles and gown.”

United Kingdom

From the UK Guidance on COVID-19: infection prevention and control. On aerosol-generating medical procedure ‘hot spots’:

The Department of Health and Social Care’s New and Emerging Respiratory Virus Threat Assessment Group (NERVTAG) have recommended that airborne precautions should be implemented at all times in clinical areas considered AGP ‘hot spots’ (e.g., intensive care units (ICU), intensive therapy units (ITU) or high dependency units (HDU) that are managing COVID-19 patients (unless patients are isolated in a negative pressure isolation room or single room, where only staff entering the room need wear a respirator).


From the Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19):

“Suspect cases are isolated in normal pressure single rooms, wear a surgical mask (for source control). Staff in China wear a cap, eye protection, N95 masks, gown and gloves (single use only).”


From their interim Infection Prevention and Control guidance. On swabbing:

“If the patient has severe symptoms suggestive of pneumonia, e.g., fever and breathing difficulty, or frequent, severe or productive coughing episodes, then contact and airborne precautions should be observed.”