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CFNU research summary on COVID-19 - updated May 19, 2020

The following document is an overview of the scientific evidence to-date as it relates to COVID-19 as well as an update on the international guidance on infection prevention and control of COVID-19. It does not purport to be a comprehensive list of all the research available. Our understanding of COVID-19 is changing daily in response to emerging science.

This research is provided for your information, but CFNU cannot guarantee its accuracy or completeness, as CFNU was not involved in reviewing or producing these resource materials.


Guidance in Canada recommends droplet and contact precautions for routine care of COVID-19 patients. Airborne precautions are recommended for aerosol-generating medical procedures.

What do we mean by droplet, contact and airborne transmission?

Droplet transmission – Usually defined as [large] respiratory droplets carrying infectious pathogens [that] transmit infection when they travel directly from the respiratory tract of the infectious individual to susceptible mucosal surfaces of the recipient, generally over short distances, necessitating facial protection.

Contact transmission – Close contact involves hand transfer of surface contamination to mouth, nose or eyes.

Airborne transmission – Is defined as dissemination of either airborne droplet nuclei or small particles in the respirable size range [aerosols] containing infectious agents that remain infective over time and distance. An important requirement of airborne transmission, according to the CDC, is that it can occur only at a long distance from the source.

Aerosols are defined as “tiny particles or droplets suspended in air.”

Source: U.S. Centers for Disease Prevention and Control

According to expert research, what is the gap in the infectious disease paradigm outlined above?

Dr. Lisa Brosseau, a national expert on respiratory protection and infectious diseases and Professor Emerita, University of Illinois, recently wrote in a commentary for the Center for Infectious Disease Research and Policy:

“Based on research now more than 70 years out of date, the infection control paradigm of contact, droplet, and airborne transmission fails to recognize inhalation of small airborne particles [aerosols] very close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.”

Why does the CFNU recommend the precautionary principle, and what is it?

We are learning more and more about COVID-19 each day, and many of the assumptions we made about COVID-19 just a few months ago have been proven wrong. For example, guidance in Canada and the U.S. has changed in favour of the public wearing homemade masks as we have discovered that asymptomatic and presymptomatic transmission account for a significant percentage of the spread of this novel coronavirus. Given the emerging science on close-range aerosol transmission (borne in the air), and past studies which suggest it is likely, the CFNU continues to recommend the precautionary principle be applied to protect health care workers, as we have from the outset.

In a nutshell, the precautionary principle, as applied to a novel, highly transmissable, virus such as this coronavirus, with a significant public health impact, requires governments and employers to begin with the highest level of protection, not the lowest, for health care workers, and then reduce the level of protection as the science emerges to justify this measure. Instead, the approach in Canada is to await scientific certainty – which could take years – to increase the level of protecton provided to health care workers on the front lines.

In the World Health Organization’s Infection prevention and control of epidemic- and pandemic-prone acute respiratory infections in health care WHO Guidelines, 2014, the WHO also supported the precautionary principle for new infectious diseases, calling for airborne and contact precautions.

“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.”

How does COVID-19 spread?

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 Proceedings of the National Academy of Sciences of the United States of America. “The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission”, May 13, 2020.

“Abstract: Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly considered to be a likely mode of disease transmission. Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per second. In a closed, stagnant air environment, they disappear from the window of view with time constants in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4 μm diameter, or 12- to 21-μm droplets prior to dehydration. These observations confirm that there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.”

From Human Genomics. “COVID-19 vulnerability: the potential impact of genetic susceptibility and airborne transmission”, May 12, 2020.

“Detection of SARS-CoV-2 in the air prompts questions about safe exposure levels. The high transmissivity of the virus suggests that a low dose might be sufficient to infect an individual; however, such studies have yet to evaluate the infectious dose of SARS-CoV-2. Until scientific evidence emerges, it is useful for individuals to follow approaches that minimize their risk of infection by reducing their exposure level and duration of exposure. Initial studies (as detailed above) report a range of airborne virus exposure levels in hospitals, as well as public spaces. The combined use of masks and physical distancing can be effective approaches for decreasing exposure to airborne forms of SARS-CoV-2. Avoiding or minimizing the time in contact with these potential aerosol exposures would also be a critical parameter in lowering risk.”

From Risk Analysis. “Consideration of the Aerosol Transmission for COVID‐19 and Public Health”, May 1, 2020.

“This article analyzes the available evidence to address airborne, aerosol transmission of the SARS‐CoV‐2. We review and present three lines of evidence: case reports of transmission for asymptomatic individuals in association with studies that show that normal breathing and talking produce predominantly small droplets of the size that are subject to aerosol transport; limited empirical data that have recorded aerosolized SARS‐CoV‐2 particles that remain suspended in the air for hours and are subject to transport over distances including outside of rooms and intrabuilding, and the broader literature that further supports the importance of aerosol transmission of infectious diseases. The weight of the available evidence warrants immediate attention to address the significance of aerosols and implications for public health protection.”

From medRxiv. “Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions”, April 18, 2020.

“We measured the dynamic (short-term) aerosol efficiencies of SARS-CoV-2 and compared the efficiencies with two other emerging coronaviruses, SARS-CoV (emerged in 2002) and Middle Eastern respiratory syndrome CoV (MERS-CoV; emerged starting in 2012). We also quantified the long-term persistence of SARS-CoV-2 and its ability to maintain infectivity when suspended in aerosols for up to 16 hours.”


“Collectively, this preliminary dataset on the aerosol efficiency and persistence of SARSCoV- 2 suggest that this virus is remarkably resilient in aerosol form, even when aged for over 12 hours, and reinforces the conclusions reached in earlier studies of aerosol fitness by others. Aerosol transmission of SARS-CoV-2, whether through direct respiratory droplet transfer or fomite generation, may in fact be a more important exposure transmission pathway than previously considered.”


“Humans produce aerosols continuously through normal respiration. Production of aerosols increases during respiratory illnesses, and even during louder-than-normal oration. A fraction of naturally-generated aerosols fall within the size distribution used in our experimental studies (<5 μm), thus leading us to the conclusion that individuals infected with SARS-CoV-2 have the capacity to produce viral bioaerosols that may remain infectious over long periods of time after production via human shedding and airborne transport.”

From SciTech Daily. “Indoor Precautions Essential to Stem Airborne COVID-19 – The World Should Face the Reality”, April 16, 2020

  • Airborne transmission of COVID-19 must be taken into account
  • Likely COVID-19 spread to cruise ship passengers through ventilation system even when passengers confined to their cabins
  • Viable airborne viruses can travel beyond 1.5m on airflow when exhaled by an infected person
  • Virus air transmission research must begin now not retrospectively

From New England Journal of Medicine (NEJM). “Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering”, April 15, 2020

“Speaking calmly and at a normal volume produces liquid droplets so small they can remain suspended in the air long enough to enter the airways of other people, potentially exposing them to viruses including the one that causes Covid-19, according to a new study led by scientists at the National Institutes of Health.”

From EID Journal (Centers for Disease Control and Prevention). “Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020 Emerging Infectious Disease”, July 2020 (early release).

In this study, SARS-CoV-2 was widely distributed in the air and on object surfaces in both the ICU and general COVID ward (GW), implying a potentially high infection risk for medical staff and other close contacts. The maximum transmission distance of SARS-CoV-2 aerosol might be up to 4 metres.

“SARS-CoV-2 was widely distributed in the air and on object surfaces in both the ICU and GW [COVID-19 General Ward], implying a potentially high infection risk for medical staff and other close contacts.”


“Half of the samples from the soles of the ICU medical staff shoes tested positive. Therefore, the soles of medical staff shoes might function as carriers.”

From Aalto University, Finland. “Researchers modelling the spread of the coronavirus emphasise the importance of avoiding busy indoor spaces”, April 6, 2020

“Aalto University, Finnish Meteorological Institute, VTT Technical Research Centre of Finland and University of Helsinki have studied how extremely small airborne aerosol particles emitted from the respiratory tract when coughing, sneezing or even talking are transported in the air. Such particles can carry pathogens such as coronaviruses. The researchers modelled a scenario where a person coughs in an aisle between shelves, like those found in grocery stores; and taking into consideration the ventilation.

The researchers obtained the same preliminary result: in the situation under investigation, the aerosol cloud spreads outside the immediate vicinity of the coughing person and dilutes in the process. However, this can take up to several minutes. ‘Someone infected by the coronavirus, can cough and walk away, but then leave behind extremely small aerosol particles carrying the coronavirus. These particles could then end up in the respiratory tract of others in the vicinity’, explains Aalto University Assistant Professor Ville Vuorinen.”

From Wiley Online Library. “Airborne transmission of severe acute respiratory syndrome coronavirus‐2 to healthcare workers: a narrative review”, April 20, 2020

“Healthcare workers should appraise the current evidence regarding transmission and apply this to the local infection prevalence. Measures to mitigate airborne transmission should be employed at times of risk. However, the mechanisms and risk factors for transmission are largely unconfirmed. Whilst awaiting robust evidence, a precautionary approach should be considered to assure healthcare worker safety.”

From Journal of Infectious Diseases. “Airborne or Droplet Precautions for Health Workers Treating Coronavirus Disease 2019?” April 16, 2020

The authors undertook a review of current international and jurisdictional guidance as well as the emerging science and concluded:

“Several studies of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) support aerosol transmission, and 1 study documented virus at a distance of 4 meters (≈13 feet) from the patient. Moreover, evidence suggests that infections cannot neatly be separated into the dichotomy of droplet versus airborne transmission routes. Available studies also show that SARS-CoV-2 can be detected in the air, and remain viable 3 hours after aerosolization. The weight of combined evidence supports airborne precautions for the occupational health and safety of health workers treating patients with COVID-19.”

From Aerosol Science and Technology. “The coronavirus pandemic and aerosols: Does COVID-19 transmit via expiratory particles?” April 3, 2020

Given the large numbers of expiratory particles known to be emitted during breathing and speech, and given the clearly high transmissibility of COVID-19, a plausible and important hypothesis is that a face-to-face conversation with an asymptomatic infected individual, even if both individuals take care not to touch, might be adequate to transmit COVID-19.

The mechanism for SARS‐CoV‐2 transmission is unknown, but the evidence suggestive of airborne spread is growing. We speculate that infected patients who cough, have high work of breathing, increased closing capacity and altered respiratory tract lining fluid will be significant producers of pathogenic aerosols. We suggest several ‘aerosol‐generating procedures’ may in fact result in less pathogen aerosolization than a dyspnoeic and coughing patient. Health care workers should appraise the current evidence regarding transmission and apply this to the local infection prevalence. Measures to mitigate airborne transmission should be employed at times of risk. However, the mechanisms and risk factors for transmission are largely unconfirmed. Whilst awaiting robust evidence, a precautionary approach should be considered to assure health care worker safety.

Preprint from medRxiv. “Detection of Air and Surface Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospital Rooms of Infected Patients”, April 9, 2020.

“Air sampling detected SARS-CoV-2 PCR-positive particles of sizes >4 μm and 1-4 μm in two rooms, which warrants further study of the airborne transmission potential of SARS-CoV-2. 56.7% of rooms had at least one environmental surface contaminated. High touch surface contamination was shown in ten (66.7%) out of 15 patients in the first week of illness, and three (20%) beyond the first week of illness (p = 0.01).”

Preprint from Environment International. “Airborne transmission of SARS-CoV-2: The world should face the reality”, June 2020

“Therefore, all possible precautions against airborne transmission in indoor scenarios should be taken. Precautions include increased ventilation rate, using natural ventilation, avoiding air recirculation, avoiding staying in another person’s direct air flow, and minimizing the number of people sharing the same environment (Qian et al. 2018). Of significance is maximizing natural ventilation in buildings that are, or can be natural ventilation and ensuring that the ventilation rate is sufficiently high.”


“To summarize, based on the trend in the increase of infections, and understanding the basic science of viral infection spread, we strongly believe that the virus is likely to be spreading through the air. If this is the case, it will take at least several months for this to be confirmed by science. This is valuable time lost that could be used to properly control the epidemic by the measures outlined above and prevent more infections and loss of life. Therefore, we plead that the international and national authorities acknowledge the reality that the virus spreads through air, and recommend that adequate control measures, as discussed above be implemented to prevent further spread of the SARS-CoV-2 virus.We predict that this failure to immediately recognize and acknowledge the importance of airborne transmission and to take adequate actions against it will result in additional cases of infection in the coming weeks and months, which would not occur if these actions were taken. The air transmission issue should be taken seriously now, during the course of the epidemic.”

From National Research Council. Rapid Expert Consultation on the Possibility of Bioaerosol Spread of SARS-CoV-2 for the COVID-19 Pandemic (April 1, 2020). Washington, DC: The National Academies Press.

 “While the current SARS-CoV-2 specific research is limited, the results of available studies are consistent with aerosolization of virus from normal breathing.”

“Individuals vary in the degree to which they produce bioaerosols through normal breathing. This may have a bearing on efficiency of transmission of SARS-CoV-2 by different infected but asymptomatic individuals.”

“…for no respiratory virus is the exact proportion of infections due to air droplet, aerosol, or fomite transmission fully established, and many individual factors and situations may contribute to the importance of each route of transmission.”

From Science, April 2, 2020: “You may be able to spread coronavirus just by breathing, new report finds”

“The National Academy of Sciences (NAS) has given a boost to an unsettling idea: that the novel coronavirus can spread through the air—not just through the large droplets emitted in a cough or sneeze. Though current studies aren’t conclusive, “the results of available studies are consistent with aerosolization of virus from normal breathing,” Harvey Fineberg, who heads a standing committee on Emerging Infectious Diseases and 21st Century Health Threats, wrote in a 1 April letter to Kelvin Droegemeier, head of the White House Office of Science and Technology Policy.”

From The Atlantic. “Everyone Thinks They are Right About Masks: How the coronavirus travels through the air has become one of the most divisive debates in this pandemic”, April 1, 2020

From medRxiv (BMJ, Yale): “Short-range airborne route dominates exposure of respiratory infection during close contact”, March 2020

In this study, the exposure to exhaled droplets during close contact (< 2 m) via both the short-range airborne and large droplet sub-routes is studied… The short-range airborne route is found to dominate at most distances studied during both talking and coughing.

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.”

From NY Times: “Infected but Feeling Fine: The Unwitting Coronavirus Spreaders”, March 31, 2020

In addition to its confusing stance on masks, “[…] the W.H.O. has been saying aerosol transmission doesn’t occur, which is also perplexing,” Dr. Cowling said, adding, “I think both are actually wrong.”
“I think increasing evidence suggests the virus is spread not just through droplets but through aerosols,” Dr. Chowell said. “It would make a lot of sense to encourage at the very least face mask use in enclosed spaces including supermarkets.”

Video (with English and Chinese subtitles) by Japanese Association for Infectious Diseases’ study on micron-sized droplets

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.”

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:

“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.”

Eyewitness News video: Interview on March 10, 2020, with Michael Osterholm, Regents Professor, McKnight Presidential Endowed Chair in Public Health, and the Director of the Center for Infectious Disease Research and Policy, in which he describes COVID-19 as an “airborne virus”.

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.

Can people without symptoms spread COVID-19?

From Alberta College of Family Physicians. “Clinical Question: What is the evidence for asymptomatic transmission of COVID-19 (including those who will remain asymptomatic and those who are early and not symptomatic yet)?”, April 14, 2020

“Bottom Line: Transmission of COVID-19 can occur in people who are currently asymptomatic. Case reports suggest this occurs in 6-13% of cases, although modeling suggests this might be higher. The importance of asymptomatic transmission is heightened by reports that ~50% of carriers are asymptomatic when an entire population (example cruise ship) is tested. Physical distancing should assist in preventing transmission from asymptomatic individuals.”

From New England Journal of Medicine. “Asymptomatic Transmission, the Achilles’ Heel of Current Strategies to Control Covid-19”, April 24, 2020

“What explains these differences in transmission and spread? A key factor in the transmissibility of Covid-19 is the high level of SARS-CoV-2 shedding in the upper respiratory tract even among presymptomatic patients.”

From New England Journal of Medicine. “Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility”, April 24, 2020

“Rapid and widespread transmission of SARS-CoV-2 was demonstrated in this skilled nursing facility. More than half of residents with positive test results were asymptomatic at the time of testing and most likely contributed to transmission. Infection-control strategies focused solely on symptomatic residents were not sufficient to prevent transmission after SARS-CoV-2 introduction into this facility.”

Preprint from medRxiv. “Can people who are asymptomatic or pre-symptomatic infect others: a systematic review of primary data?”, April 16, 2020

“Implications for healthcare workers protection and health systems response: Asymptomatic and pre-symptomatic patients are a source of active risk for front line workers. It imposes an additional challenge to the health system as undetected patients can spread the infection and affect the level of response. The use of personal protective equipment by all front-line workers should be mandatory. Shortages of masks, goggles are unacceptable because the risk of infection and death of these workers may affect the whole health system response to the community.”

Are surgical masks – designed for droplet and contact precautions – adequate respiratory protection in light of what we are learning about 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 U.S. Food and Drug Administration (FDA): N95 Respirators and Surgical Masks (Face Masks)

“While a surgical mask may be effective in blocking splashes and large-particle droplets, a face mask, by design, does not filter or block very small particles in the air that may be transmitted by coughs, sneezes, or certain medical procedures. Surgical masks also do not provide complete protection from germs and other contaminants because of the loose fit between the surface of the face mask and your face.

Surgical masks are not intended to be used more than once. If your mask is damaged or soiled, or if breathing through the mask becomes difficult, you should remove the face mask, discard it safely, and replace it with a new one. To safely discard your mask, place it in a plastic bag and put it in the trash. Wash your hands after handling the used mask.

An N95 respirator is a respiratory protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles.

The ‘N95’ designation means that when subjected to careful testing, the respirator blocks at least 95 percent of very small (0.3 micron) test particles. If properly fitted, the filtration capabilities of N95 respirators exceed those of face masks.”

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 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?


From Military Medical Research: A rapid advice guideline for the diagnosis and treatment of 2019 novel coronavirus (2019-nCoV) infected pneumonia (standard version). Jin, Y.-H. et al. (2020) (

This rapid advice guideline is suitable for the first frontline doctors and nurses, managers of hospitals and healthcare sections, community residents, public health persons, relevant researchers, and all person who are interested in the 2019-nCoV.

From Zhejiang University School of Medicine: Liang,T. Dr. (Ed.) Handbook of C0VID-19 Prevention and Treatment: compiled according to clinical experience from The First Affiliated Hospital

This handbook is based on the guidelines on prevention, control, diagnosis and treatment by the National Health Commission of China. It summarizes the first-hand clinical experience in how to diagnose, screen and treat COVID-19 patients, particularly critically ill patients, and it serves as a point of reference for other countries battling the pandemic.

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

Swabbing: Collecting diagnostic respiratory samples (e.g., nasopharyngeal swab) can provoke coughing and/or sneezing and therefore lead to the production of aerosols. Health care workers collecting diagnostic respiratory samples in enclosed spaces should wear gloves, eye protection, a gown and a surgical mask or, if available, an FFP.

Confirmed or suspected cases: Health care workers in contact with a suspected or confirmed COVID-19 case should wear a surgical mask or, if available, an FFP2 respirator tested for fitting, eye protection (i.e. visor or goggles), a long-sleeved gown or apron, and gloves.

United Kingdom

PPE for higher-risk acute inpatient care areas:

Long-sleeved disposable fluid repellent gowns, FFP3 respirators, eye protection and gloves must be worn in higher-risk areas containing possible or confirmed cases, or as indicated by local risk assessment. If non-fluid-resistant gowns are used, a disposable plastic apron should be worn underneath. Gloves and aprons are subject to single use as per Standard Infection Control Precautions (SICPs) with disposal after each patient contact. Gowns, respirators and eye protection may be subject to single session use (Section 6 of COVID-19 personal protective equipment (PPE) guidance).

A higher-risk acute inpatient care area is defined as a clinical environment where AGPs are regularly performed.

Higher-risk acute care areas include:

  • intensive care and high dependency care units (ICU or HDU)
  • emergency department resuscitation areas
  • wards or clinical areas where AGPs are regularly performed (such as wards with NIV or CPAP)
  • operating theatres, where AGPs are performed
  • endoscopy units, where bronchoscopy, upper gastrointestinal or nasoendoscopy are performed