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CFNU research summary on COVID-19 - Updated August 4, 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Based on research now more than 70 years out of date, the infection control paradigm of contact, droplet, and airborne transmission fails to recognize inhalation of small airborne particles [aerosols] very close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 for pandemic-prone novel viruses.

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 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 New York Times. Marr, Linsey C. “Yes, the Coronavirus is in the Air”, July 30, 2020

“I believe that, taken together, much of the evidence gathered to date suggests that close-range transmission by aerosols is significant — possibly very significant, and certainly more significant than direct droplet spray.

From SSRN Guenther, T. et al. “Investigation of a superspreading event preceding the largest meat processing plant-related SARS-Coronavirus 2 outbreak in Germany”, July 23, 2020

“Interpretation: Our results indicate climate conditions and airflow as factors that can promote efficient spread of SARS-CoV-2 via distances of more than 8 meters and provide insights into possible requirements for pandemic mitigation strategies in industrial workplace settings.”

From medRxiv. Santarperia, J.L. et al. “The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol”, July 21, 2020

“Conclusion: Our results demonstrate that SARS-CoV-2 RNA exists in respired aerosols less than 5 µm in diameter; that aerosols containing SARS-CoV-2 RNA exist in particle modes that are produced during respiration, vocalization, and coughing; and that some fraction of the RNA-containing aerosols contain infectious virions. This study supports the use of efficient respiratory protection and airborne isolation precautions to protect from exposure to fine SARS-CoV-2 aerosol when interacting with infected individuals, regardless of symptoms or medical procedure being performed.

From McMaster University National Collaborating Centre for Methods and Tools. “COVID-19 Summary SARS-CoV-2 Virus Airborne Transmission”, Prepared for the Public Health Agency of Canada, July 10, 2020 (completed); July 24, 2020 (submitted)

“Overview of the Evidence: Publications appearing in the emerging literature up to July 7, 2020 have informed this evidence brief. The available body of evidence is limited, largely theoretical, and does not specifically consider SARS-CoV-2 infectious dose or confirm the infectiousness of airborne particles. The theoretical and modeling evidence is of good quality. The available empirical and modeled evidence indicates there is some risk of SARS-CoV-2 virus laden aerosol and droplet dispersion at distances beyond two meters, while epidemiological evidence implicates airborne transmission of SARS-CoV-2 to have occurred in some indoor settings. Airborne infection transmission risks appear to be amplified in low temperature high humidity conditions, as well as in crowded and poorly ventilated areas where infected individuals may cough or speak loudly (i.e. sing, scream).” 

From MIT Technology Review. Patel, Neel V. “If the coronavirus is really airborne, we might be fighting it the wrong way”, July 11, 2020

“One of the biggest questions we still have about COVID-19 is how much of a viral load is needed to cause infection. The answer changes if we think it is aerosols that we need to worry about. Smaller particles won’t carry as large a viral load as bigger ones, but because they can linger in the air for much longer, it may not matter—they’ll build up in larger concentrations and get distributed more widely the longer an infected person is around to expel aerosolized virus. 

The more people you have coming in and out of an indoor space, the more likely it is that someone who is infected will show up. The longer those infected individuals spend in that space, the higher the concentration of virus in the air over time.”

From Oxford Academic: Clinical Infectious Diseases. Morawska, L., Milton, D. and 237 scientists from 32 countries who support this Commentary. “It is Time to Address Airborne Transmission of COVID-19.”, July 6, 2020

“Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1 to 2 m from an infected individual. […] It is understood that there is not as yet universal acceptance of airborne transmission of SARS-CoV2; but in our collective assessment there is more than enough supporting evidence so that the precautionary principle should apply. In order to control the pandemic, pending the availability of a vaccine, all routes of transmission must be interrupted. We are concerned that the lack of recognition of the risk of airborne transmission of COVID-19 and the lack of clear recommendations on the control measures against the airborne virus will have significant consequences: people may think that they are fully protected by adhering to the current recommendations, but in fact, additional airborne interventions are needed for further reduction of infection risk. […] The evidence is admittedly incomplete for all the steps in COVID-19 microdroplet transmission, but it is similarly incomplete for the large droplet and fomite modes of transmission. The airborne transmission mechanism operates in parallel with the large droplet and fomite routes, that are now the basis of guidance. We appeal to the medical community and to the relevant national and international bodies to recognize the potential for airborne spread of COVID-19. There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or room scale), and we are advocating for the use of preventive measures to mitigate this route of airborne transmission.”

From Atmosphere. Carducci, A. et al. “Covid-19 Airborne Transmission and Its Prevention: Waiting for Evidence or Applying the Precautionary Principle?” July 3, 2020

“Besides the predominant ways of transmission of SARS-CoV-2 (namely, contacts and large droplets) the airborne one is increasingly taken into consideration as a result of latest research findings. Nevertheless, this possibility has been already suggested by previous studies on other coronaviruses including SARS-CoV and MERS-CoV. To describe the state of the art of coronaviruses and airborne transmission, a systematic review was carried out using the PRISMA methodology. Overall, 64 papers were selected and classified into three main groups: laboratory experiments (12 papers), air monitoring (22) and epidemiological and airflow model studies (30). The airborne transmission of SARS-CoV-2 is suggested by the studies of the three groups, but none has yet obtained complete evidence. […] epidemiological investigations only hypothesize the airborne transmission as a possible explanation for some illness cases, but without estimating its attributable risk. Nevertheless, while waiting for more evidence, it is urgent to base advice on preventive measures, such as the use of masks, safe distancing and air ventilation, on the precautionary principle.”

From Emerging Infectious Diseases Journal (Centers for Disease Control and Prevention). Fears, A.C. et al. “Persistence of severe acute respiratory syndrome coronavirus 2 in aerosol suspensions”, June 22, 2020

“We aerosolized severe acute respiratory syndrome coronavirus 2 and determined that its dynamic aerosol efficiency surpassed those for severe acute respiratory syndrome coronavirus and Middle East respiratory syndrome. Although we performed [the] experiment only once across severeral laboratories, our findings suggest retained infectivity and virion integrity for up to 16 hours in respirable-sized aerosols.”

From Proceedings of the National Academy of Sciences of the United States of America. Zhang, R. et al. “Identifying airborne transmission as the dominant route for the spread of COVID-19”, June 11, 2020

“The inadequate knowledge on virus transmission has inevitably hindered development of effective mitigation policies and resulted in unstoppable propagation of the COVID-19 pandemic. In this work, we show that airborne transmission, particularly via nascent aerosols from human atomization, is highly virulent and represents the dominant route for the transmission of this disease.”

From medRxiv. Evans, M. “Avoiding COVID-19: Aerosol Guidelines”, June 4, 2020

“The COVID-19 pandemic has brought into sharp focus the need to understand respiratory virus transmission mechanisms. In preparation for an anticipated influenza pandemic, a substantial body of literature has developed over the last few decades showing that the short-range aerosol route is an important, though often neglected transmission path. We develop a simple mathematical model for COVID-19 transmission via aerosols, apply it to known outbreaks, and present quantitative guidelines for ventilation and occupancy in the workplace.”

From medRxiv. Santarpia, J.L. et al.”Aerosol and Surface Transmission Potential of SARS-CoV-2”, June 3, 2020

“During the initial isolation of 13 individuals with COVID-19 at the University of Nebraska Medical Center, we collected air and surface samples to examine viral shedding from isolated individuals. We detected viral contamination among all samples, indicating that SARS-CoV-2 may spread through both direct (droplet and person-to-person) as well as indirect mechanisms (contaminated objects and airborne transmission). Taken together, these finding support the use of airborne isolation precautions when caring for COVID-19 patients.”

From medRxiv. Ma, J. et al. “Exhaled breath is a significant source of SARS-CoV-2 emission”, June 2, 2020

Here, 35 COVID-19 subjects were recruited; exhaled breath condensate (EBC), air samples and surface swabs were collected and analyzed for SARS-CoV-2 using reverse transcription-polymerase chain reaction (RT-PCR). EBC samples had the highest positive rate (16.7%, n=30), followed by surface swabs (5.4%, n=242), and air samples (3.8%, n=26). COVID-19 patients were shown to exhale SARS-CoV-2 into the air at an estimated rate of 103-105 RNA copies/min; while toilet and floor surfaces represented two important SARS-CoV-2 reservoirs. Our results imply that airborne transmission of SARS-CoV-2 plays a major role in COVID-19 spread, especially during the early stages of the disease.”

From Nature. Chia, P.Y. et al. “Detection of Air and Surface Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospital Rooms of Infected Patients”, May 29, 2020.

Understanding the particle size distribution in the air and patterns of environmental contamination of SARS-CoV-2 is essential for infection prevention policies. Here we screen surface and air samples from hospital rooms of COVID-19 patients for SARS-CoV-2 RNA. Environmental sampling is conducted in three airborne infection isolation rooms (AIIRs) in the ICU and 27 AIIRs in the general ward. 245 surface samples are collected. 56.7% of rooms have at least one environmental surface contaminated. High touch surface contamination is 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, χ2 test). Air sampling is performed in three of the 27 AIIRs in the general ward, and detects SARS-CoV-2 PCR-positive particles of sizes >4µm and 1–4µm in two rooms, despite these rooms having 12 air changes per hour. This warrants further study of the airborne transmission potential of SARS-CoV-2.”

From Environment International. Morawska, L. et al. “Correspondence: How can airborne transmission of COVID-19 indoors be minimised?” May 27, 2020

Inhaling small airborne droplets is probable as a third route of infection, in addition to more widely recognized transmission via larger respiratory droplets and direct contact with infected people or contaminated surfaces. While uncertainties remain regarding the relative contributions of the different transmission pathways, we argue that existing evidence is sufficiently strong to warrant engineering controls targeting airborne transmission as part of an overall strategy to limit infection risk indoors. Appropriate building engineering controls include sufficient and effective ventilation, possibly enhanced by particle filtration and air disinfection, avoiding air recirculation and avoiding overcrowding. Often, such measures can be easily implemented and without much cost, but if only they are recognised as significant in contributing to infection control goals. We believe that the use of engineering controls in public buildings, including hospitals, shops, offices, schools, kindergartens, libraries, restaurants, cruise ships, elevators, conference rooms or public transport, in parallel with effective application of other controls (including isolation and quarantine, social distancing and hand hygiene), would be an additional important measure globally to reduce the likelihood of transmission and thereby protect healthcare workers, patients and the general public.”

From Lancet. Somsen, G.A. et al. “Small droplet aerosols in poorly ventilated spaces and SARS-CoV-2 transmission.” May 27, 2020

“This study shows that better ventilation of spaces substantially reduces the airborne time of respiratory droplets. This finding is relevant because typically poorly ventilated and populated spaces, like public transport and nursing homes, have been reported as sites of viral transmission despite preventive physical distancing. The persistence of small respiratory droplets in such poorly ventilated spaces could contribute to the spread of SARS-CoV-2. Our findings confirm that improving ventilation of public spaces will dilute and clear out potentially infectious aerosols. To suppress the spread of SARS-CoV-2 we believe health-care authorities should consider the recommendation to avoid poorly ventilated public spaces as much as possible. The implications are also important for hospital settings where aerosolisation by coughing and medical treatments and close contact with COVID-19 patients is very common.”

From Proceedings of the National Academy of Sciences of the United States of America. Stadnytskyi, V. et al. “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 BMC Human Genomics. Godri Pollitt, K.J. et al. “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 Preprints. Allen, J.; Marr, L. “Re-thinking the Potential for Airborne Transmission of SARS-CoV-2”, May 7, 2020

While the traditional distinction between “droplet” and “airborne” transmission of infectious disease has been useful for setting guidelines on the use of personal protective equipment, it has also established a false dichotomy in understanding the behavior of viruses in the air. Viruscontaining droplets that are released by breathing, talking, and coughing span a continuum of sizes, from 0.01 to hundreds of microns. It is impossible for someone to release “large droplets” (>5 microns) without also releasing smaller ones.xii Thus, transmission that is purported to occur via the spray of large droplets from a cough could in fact be occurring through inhalation of much smaller droplets at close range. In fact, a physics-based simulation suggests that the majority of exposure at close range occurs by inhalation of small droplets rather than by contact with large droplets that land on the mouth, nose, and eyes, unless the people are closer than 30 cm or the droplets are very large.”

From Risk Analysis. Anderson, E. et al. “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 International Journal of Environmental Research and Public Health. Setti, L. et al. “Airborne Transmission Route of COVID-19: Why 2 Meters/6 Feet of Inter-Personal Distance Could Not Be Enough” April 23, 2020

However, recently published studies support the hypothesis of virus transmission over a distance of 2 m from an infected person. Researchers have proved the higher aerosol and surface stability of SARS-COV-2 as compared with SARS-COV-1 (with the virus remaining viable and infectious in aerosol for hours) and that airborne transmission of SARS-CoV can occur besides close-distance contacts. Indeed, there is reasonable evidence about the possibility of SARS-COV-2 airborne transmission due to its persistence into aerosol droplets in a viable and infectious form. Based on the available knowledge and epidemiological observations, it is plausible that small particles containing the virus may diffuse in indoor environments covering distances up to 10 m from the emission sources, thus representing a kind of aerosol transmission.”

From Anaesthesia. Wilson, N.M. et al. “Review article: Airborne transmission of severe acute respiratory syndrome coronavirus‐2 to healthcare workers: a narrative review”, April 20, 2020

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.”

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

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 Journal of Infectious Diseases. Bahl, P. et al. “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 SciTech Daily. Queensland University of Technology. “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). National Institutes of Health. Correspondence: “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 Emerging Infectious Diseases Journal (Centers for Disease Control and Prevention) Vol 26; No. 7. Guo, Z-D. et al. “Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China 2020”, April 10, 2020

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.” The maximum transmission distance of SARS-CoV-2 aerosol was measured at up to 4 metres. […]

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. Aalto University; Finnish Meteorological Institute; VTT Technical Research Centre and University of Helsinki. “Researchers modelling the spread of the coronavirus emphasise the importance of avoiding busy indoor spaces”, April 6, 2020

“…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 Aerosol Science and Technology. Asadi, S. et al. “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.

From Environment International. Vol. 139. Morawska, L.; Cao, J. “Airborne transmission of SARS-CoV-2: The world should face the reality”

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 the National Academies of Science and Engineering.”Rapid Expert Consultation on the Possibility of Bioaerosol Spread of SARS-CoV-2 for the COVID-19 Pandemic”, April 1, 2020

 “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 medRxiv. Santarpia, J.L. et al. “Transmission Potential of SARS CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center”, 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.”

From Building and Environment. Vol. 176. Cheng, W. et al. “Short-range airborne route dominates exposure of respiratory infection during close contact”, March 20, 2020

“Highlights:

The smaller the exhaled droplets, the more important the short-range airborne route.

Exhalation velocity impacts significantly on droplet travel distance and size change.

The large droplet route only dominates when the subjects are within 0.2 m while talking or 0.5 m while coughing.

The large droplet route contributes less than 10% of exposure when the droplets are smaller than 50 μm at 0.3 m apart.”

From Occupational Health Clinics for Ontario Workers Inc. “A Consideration of the Rationale Provided to Downgrade PPE Precautions for COVID‐19”, March 31, 2020

“The evidence provided by the Public Health Ontario can be characterized as “proof by absence of evidence.”

“The large number of papers on the measurement of airborne virus strongly suggest that this is a pathway not to be overlooked.In fact, the paper by Yin et al (2019 – which includes Allison McGeer, James Scott and Samira Mubareka, as co‐authors describing research done in Toronto with the help of NIOSH (and published in the Journal of Occupational and Environmental Hygiene)) has the following few sentences on this topic: “The conventional paradigm is to classify respiratory pathogen transmission as droplet vs. airborne, with clear policies and procedures for each purported mode of transmission. Where there is doubt, both droplet and airborne precautions are generally employed. Large respiratory droplets are >10 µm in diameter and are involved in short-range (2 m) airborne transmission;[15] these respirable particles are small enough to be inhaled into the alveoli. The relative contribution of each route to overall transmission of influenza is unknown, leading to debate regarding the important mode(s) of transmission and appropriate means of transmission prevention.”

From The Online Citizen: Hakeem, D. “Medical experts from China and S. Korea underline importance of wearing mask during COVID-19 pandemic – contrary to WHO’s recommendation”, March 30, 2020.

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.” Dr. Kim Woo-joo, is a professor of infectious diseases at the Korea University Guro Hospital and South Korea’s most prominent coronavirus expert:

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

Review of the Literature Commissioned by the National Union of Public and General Employees (NUPGE) on the modes of transmission for COVID-19. Dr. John H Murphy, Adjunct Professor of Dalla Lana School of Public Health, University of Toronto, and President of Resource Environmental Associates Limited. March 19, 2020.

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.”

From Center for Infectious Disease Research and Policy. Brosseau, L. “Commentary: COVID-19 transmission messages should hinge on science”, March 16, 2020

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.”

From Council of the Canadian Academies. “Influenza Transmission Influenza Transmission and the Role of Personal Protective Respiratory Equipment: and the Role of Personal Protective Respiratory Equipment: and the Role of Personal Protective Respiratory Equipment: An Assessment of the Evidence” December 17, 2007

There is evidence that influenza is transmitted primarily at short range.

There is evidence that influenza can be transmitted via inhalation of tracheobronchial and alveolarsized particles at short range.

There is evidence that deposition of nasopharyngeal-sized particles in the upper respiratory tract can cause infection.

There is evidence that contact transmission can occur. The current weight of evidence suggests that transmission of influenza by inhalation is more probable than by indirect contact.

Can people without symptoms spread COVID-19?

From New England Journal of Medicine. Arons, M.M. et al. “Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility”, May 28, 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.”

From New England Journal of Medicine. Gandhi, M. et al. “Editorial: 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 medRxiv. Nelson, A-D. “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.”

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.”

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

From The Lancet. Fennelly, K.P. “Particle sizes of infectious aerosols: implications for infection control”, July 24, 2020

“The global pandemic of COVID-19 has been associated with infections and deaths among health-care workers. This Viewpoint of infectious aerosols is intended to inform appropriate infection control measures to protect health-care workers. Studies of cough aerosols and of exhaled breath from patients with various respiratory infections have shown striking similarities in aerosol size distributions, with a predominance of pathogens in small particles (<5 µm). These are immediately respirable, suggesting the need for personal respiratory protection (respirators) for individuals in close proximity to patients with potentially virulent pathogens. There is no evidence that some pathogens are carried only in large droplets. Surgical masks might offer some respiratory protection from inhalation of infectious aerosols, but not as much as respirators. However, surgical masks worn by patients reduce exposures to infectious aerosols to health-care workers and other individuals. The variability of infectious aerosol production, with some socalled super-emitters producing much higher amounts of infectious aerosol than most, might help to explain the epidemiology of super-spreading. Airborne infection control measures are indicated for potentially lethal respiratory pathogens such as severe acute respiratory syndrome coronavirus 2.”

From World Health Organization. “Advice on the use of masks in the context of COVID-19”, June 5, 2020

Whereas medical masks filter 3 micrometre droplets, respirators must filter more challenging 0.075 micrometre solid particles.”[…] “Therefore, the layers of the filtration material and the FFR [filtering facepiece respirator] shape, ensuring outer edges of the FFR seal around wearer’s face, result in a guaranteed claimed filtration when worn compared to the open shape, or leaking structure, of medical masks.”

From BMJ. Liu, M. et al. “Use of personal protective equipment against coronavirus diseases 2019 by healthcare professionals in Wuhan, China cross sectional study”, June 2, 2020

“OBJECTIVE: To examine the protective effects of appropriate personal protective equipment for frontline healthcare professionals who provided care for patients with coronavirus disease 2019 (covid-19). RESULTS During the deployment period in Wuhan, none of the study participants reported covid-19 related symptoms. When the participants returned home, they all tested negative for SARSCoV-2.”

From CBC. “Keep wearing masks and social distancing — it works, new McMaster study says” The Canadian Press. Refers to WHO funded research published in Lancet by Chu, D.K. et al. “Physical distancing, face masks and eye protection to prevent person-to-person transmission of SARS-Cov-2 and COVID-19: a systemic review and metaanlysis”, June 1, 2020

“Researchers concluded single-layer cloth masks are less effective than surgical masks, while tight-fitting N95 masks provide the best protection. A distance of 1 metre (more than 3 feet) between people lowers the danger of catching the virus, while 2 metres (about 6 1/2 feet) is even better.”

From The Lancet. MacIntyre, R.; Wang, Q. “Comment: Physical distancing, face masks, and eye protecton for prevention of COVID-19.”, June 1, 2020

For health-care workers on COVID-19 wards, a respirator should be the minimum standard of care. This study by Chu and colleagues should prompt a review of all guidelines that recommend a medical mask for health workers caring for COVID-19 patients. Although medical masks do protect, the occupational health and safety of health workers should be the highest priority and the precautionary principle should be applied. Preventable infections in health workers can result not only in deaths but also in large numbers of health workers being quarantined and nosocomial outbreaks which is an unacceptable risk for front-line workers. To address global shortages of PPE, countries should take responsibility for scaling up production rather than expecting health workers to work in suboptimum PPE.”

From a 2017 study: MacIntyre, R. et al. “The efficacy of medical masks and respirators against respiratory infection in healthcare workers”

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.

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) referencing a study by the Institute of Medicine of the National Academies:

“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 the purpose of protecting the wearer against entry of infectious aerosolized particles potentially surrounding the wearer and his mask.”