New W.H.O. Guideline on N-95 Use by Health Care Workers: A Preliminary Report and Literature-Based Critique

by: Laurence Svirchev, CIH, MA, BSc., ©Laurence@Svirchev.com

updated January 22, 2022

Abstract:

The World Health Organization (W.H.O.) on December 22, 2021 recommended the Health Care Workers (HCW) entering the room of a confirmed or suspected COVID-19 positive patient wear a fit tested filtering face piece respirator (FFR). The recommendation signals the long sought recognition for the use of FFR by HCW. The recommendation contains a number of provisos with weakens its significance. It also telegraphs a recognition that the hegemony of the long-dominant, but scientifically weak, droplet precautions model of SARS-CoV-2 transmission is collapsing. This report discusses:

  • A  recognition that the hegemony of the long-dominant, but scientifically weak droplet precautions model of SARS-CoV-2 transmission is collapsing
  • The Generation of Aerosols in the Near, Total Room, and Remote Fields
  • Analysis:
    • The HCW Experience (pre-vaccine) in Wuhan, China
    • The Strength of Evidence of Aerosol Transmission
    • How W.H.O. Sidesteps Aerosol Transmission
    • Recommendations and Resources for Pandemic Occupational Prevention Controls

Introduction

On December 22, 2021, the World Health Organization (W.H.O.) issued new Recommendations On Mask Use By Health Workers1. The most important component of the Recommendation is the recognition that NIOSH-approved N95 or equivalent respirators (FFR) should be worn by health care workers (HCW) before entering a room where there is a patient with suspected or confirmed COVID-19. Importantly, the recommendation includes Long Term Care workers (LTC). In previous recommendations up to October 2, 2021 the use of FFR was limited to high hazard aerosol generating procedures (AGP).

The recommendation includes a brief discussion of ventilation related to room entry as well as other forms of personal protective equipment (PPE) such as gowns and gloves. The recommendation is called “interim” with the rationale that it is issued “in light of the rapid spread of the Omicron variant of concern of SARS-CoV-2.” Significantly, W.H.O. states the recommendation is “based on on very low certainty evidence.”

This report will demonstrate that W.H.O. has not considered the totality of evidence concerning aerosol transmission, the efficacy of FFR in protecting HCW, and even clinical experience in the treatment and care of patients. The proviso of “very low certainty evidence” is with certitude false, and can only weaken the necessity for HCW to use FFR as a fundamental way of protecting themselves. 

On the following day (December 23) the Public Health Agency of Canada (PHAC) issued a similar but more limited update2 with regard to FFR. PHAC’s recommendation calls for the use of a “well fitted respirator” along with other personal protective equipment (PPE) during “direct patient care” of patients with confirmed or suspected COVID-19. The definition of “direct patient care” is not specified, and is subject to limiting the physical care of patients in clinical/medical interventions. Nor does PHAC define which occupations provide direct patient care. Importantly, it makes no reference to Canadian Standards Institute standard CSA Z94.4-18 “Selection, Use and Care of Respirators” or to the globally accepted ventilation standard ANSI/ASHRAE Standard 62.1-2019, Ventilation for Acceptable Indoor Air Quality.

Both of these announcements appear to have escaped public and media attention given the timing of the pre-holiday periods in the United States and Canada. This report discusses:

  • The significance of the W.H.O. and PHAC recommendation;
  • The Generation of Aerosols in the Near Field and Total Field
  • Analysis of the Recommendations, including
  • The HCW Experience (pre-vaccine) in Wuhan, China
  • The Strength of Evidence of Aerosol Transmission
  • How W.H.O. Sidesteps Aerosol Transmission
  • Recommendations and Resources for Pandemic Occupational Prevention Controls

Significance

The W.H.O. recommendation signals the long sought recognition for the use of FFR for all HCW coming into contact with confirmed or suspected COVID-19 patients. It also telegraphs a  recognition that the hegemony of the long-dominant, but scientifically weak droplet precautions model of SARS-CoV-2 transmission is collapsing. This report summarizes with representative examples the massive literature that demonstrates by clinical experience, biological plausibility, and physical science the very real transmission of SARS-CoV-2 by aerosols. It also discusses one of the principal means to prevent infection in HCW, the consistent use of the use of fit-tested FFR as PPE in multiple health care settings.

Previously, multiple public health jurisdictions have only allowed HCW performing aerosol generating procedures (AGP) to use fit-tested respirators. Part of this rationale was to preserve the supply of disposable respirators, even though they are now readily available even for the public. The real issue, however, is that W.H.O. and multiple national public health government organizations have long actively denied aerosol transmission, stating that there is no evidence to support this mode of transmission. On the other hand, adherents of droplet precautions as the principal mode of COVID-19 infection have proved incapable of evidencing a coherent rationale that explains four international waves of the disease, certainly because no such rationale exists.

On this basis, other HCW such as Practical Nurses, Care Aids and Longterm Care workers have often been denied and prevented from protecting themselves with FFR by administrative policies based on antiquated thinking. There have been multiple reports in Canada of HCW, even medical doctors, being disciplined when they protected themselves with FFR in violation of administrative policies.

Some national W.H.O. Member countries such as Canada have already adopted and published a weak variation on the W.H.O. recommendation. This report does not discuss the complex and confusing US CDC’s approach to protecting HCW. It will take time and struggle for the national, state/provincial and local jurisdictions of all countries to adopt the recommendation and put it into effect. 

Local public health jurisdictions, individual workers in healthcare, Unions, and Joint Occupational Health and Safety Committees and importantly citizen scientists, parents, and activists can now point to the recommendations of the world’s leading health body to justify and require the use of FFR to break the chains of transmission, and to hold their jurisdictions to a higher level of accountability.  Developing nations, unless their supply chain is deliberately enhanced by donors, will most likely lag in the use of FFR, in the same way they have lagged in vaccination rates due to inequity. 

The Generation of Aerosols in the Near Field and Total Field

AGP include intubation and extubation, manual and mechanical ventilation, airway suctioning and multiple other procedures (Table 1, Jackson et al3). These procedures create greater than normal positive and negative pressures within the respiratory system, generating ballistic infected aerosols on the outflow directly into the breathing zone of medical workers. 

Aerosol generation is often described as “close range” and “long range” but in this report, the immediate volume around the breathing zone of both patient and medical providers is characterized as the “Near Field” and the volume of the whole room as “Total Field”. A third field is the “remote field” as demonstrated during SARS-1 in the Hong Kong Amoy Gardens of which the infection spread horizontally through apartments on the same floor and vertically to other floors  via a chimney effect, “through the sewage-disposal system, person-to-person contact, and the use of communal facilities such as elevators and staircases4.” 

There has been no disagreement about the need for FFR in the near field. However aerosols in the total field have not in the past been accepted by W.H.O. as circumstances requiring the use of FFR. For the record, a W.H.O. team was part of the Amoy Gardens remote field investigation during SARS-14.

The concept of droplet precautions is inherently limited, since it does not take account of the total field in hospital rooms and other indoor environments. In reality, aerosol exhaled from the respiratory system will spread four-dimensionally and dynamically as turbulent gas clouds according to ambient conditions that include temperature, humidity, ventilation system settings as in Bourouiba5. A nicely done animated computer visualization in the NY Times illustrates aerosol spread into the total field by a standing person who coughs in the presence of three other people. It should be remembered that during SARS-1, the medical profession often referred to the arbitrary ‘three-foot rule’ (1m) which, in the time of SARS-CoV-2, was equally arbitrarily changed to a six-foot (2m) rule6.

Because it specifically mentions a room where there is a patient with suspected or confirmed COVID-19 patient, the W.H.O. recommendation goes well beyond direct clinical care in the near field by MDs, surgeons, dentists, nurses, and respiratory technologists exposed to ballistic aerosols. Long Term Care workers are specifically mentioned but they are not the only providers who enter the total field of a patient’s room. An occupational cadre of licensed practical nurses, phlebotomy technicians, care aids, housekeeping, food delivery service, social/religious workers, and others regularly enter patients’ rooms. These occupational classifications are compiled in Table 1 of Jackson et al3.

Provisos

W.H.O.’s rationale for the interim change in guidance is related to the to the infectivity of the Omicron variant which has caused a tremendous increase in the number of cases as of January, 20227. Critically, the recommendation is based on “very low certainty evidence” concerning the effectiveness of respirators versus medical masks in health care settings. A third proviso is that W.H.O. leaves the choice of respiratory protection to HCW discretion expressed in values, perceptions, and preferences. In Canada this loose approach to safe work procedures is known as a Point of Care Risk Assessment (PCRA)2. The guideline also recognizes, with validly, that the health care systems of many low income countries do not have mass access to FFR.

Analysis

The Recommendation is a measure that occupation health scientists, hygienists, engineers, their professional associations and labor representatives have long fought for. When implemented the recommendation will go a very long way in breaking the chains of transmission and not just with HCW. A respirator that seals well with the skin of the face will also protect workers in workplaces other than healthcare. It will also limit the amount of particulate that infected but asymptomatic workers can transmit.

Unfortunately, W.H.O.’s rationale of Omicron serves as a logic of convenience, a dubious proposition that explains very little to limit the accelerated spread of a new variant except for the emphasis on urgency. W.H.O. could have proposed exactly the same recommendation with the appearance of the ∆-variant or even the same prevention measures as target goals at the beginning of the pandemic in April of 2020. As will be shown in the literature this report examines, there is no conceivable rationale for the recommendation to be “interim.” W.H.O. has not used its resources to break with droplet thinking and find a contemporary scientific explanation for the power of SARS-CoV-2 transmission.

If W.H.O., PHAC of Canada, and the US CDC had accepted the validity of aerosol transmission at the beginning of the pandemic as a precautionary principle approach, countless lives would have been saved and suffering prevented. At that time, the medical and scientific world already had the China HCW experience to learn from, as well as decades of research in occupational aerosol science. The next sections are divided into the China experience; the strength of the evidence; and a commentary about W.H.O./PHAC side-stepping the scientific discussion about aerosol transmission

The HCW Experience (pre-vaccine) in Wuhan, China

An early report on the pre-vaccine HCW Experience in Wuhan, China by Zhan, et al8 in a letter to the Editor of the New England Journal of Medicine stated that during the first five or so weeks of the epidemic, a total of 3,387 HCW had been infected, or 4% of the total infected population. Eventually there were also 23 HCW deaths resulting from infection in this first period. 

Around the end of January 2020, China began a national mobilization, staged over time, of HCW to staff two new COVID-dedicated field hospitals and other pre-existing hospital to relieve Hubei province and Wuhan city’ exhausted HCW. The total number of HCW eventually reached 42,600. This mobilization was one of the key factors that brought the number of daily new infections and deaths to a few per day by April 30, 20209. The authors state that none of the HCW in this cadre of 42,600 were known to be infected by SARS-CoV-2 by the time the Hubei province-Wuhan city epidemic had ended. The authors did not discuss how HCW were protected to achieve this low rate of infection and mortality. 

From the point of view of action based research, however, evidence can also be demonstrated by real life activities. Publicly accessible media show that when the medical volunteers went to Wuhan, HCW had adopted a universal occupational use of N95 and one-piece hooded tyvek suits, glasses, and gloves for HCW treating COVID-19 patients. Numerous videos have been posted on the internet showing HCW using such PPE (example: https://www.youtube.com/watch?v=os4yemZA6Qc).

The first photo shows an MD in a patient recovery room in Wuhan. The MD is Dr Zhang Jixian (who had diagnosed the first three cases of “Pneumonia of Unknown Etiology” in December 20190. The second shows Nurse Xu holding a mobile phone with a picture of her in PPE  in a patient recovery room. The third photo shows a nasal swab being taken in Beijing in  January 2022: the engineered control totally isolates the citizen at a testing station in Beijing from the worker

With regard to HCW, in a cross-sectional study Liu et al10 reported that none of 420 HCW (116 doctors and 304 nurses) deployed from Guangzhou to two Wuhan hospitals for treating COVID-19 patients tested positive to COVID-19. Table 2 of the study shows that all of the participants worked in both intensive care and regular wards, used both AGP and non-aerosol generating procedures, and wore N95 respirators and surgical masks simultaneously, as well as other body-covering PPE.

Zhan et al.11 reported that designated COVID-19 hospitals adopted Level 3 protection by order of China’s National Health Commission: “After comparing the existing recommendations, all designated COVID-19 hospitals adopted the recommendations endorsed by the WHO for filovirus disease (Ebola). The recommendation ensures protection from head to toe using the coveralls (not the gown), thus minimizing any areas of skin exposure, in combination with the lockdown of designated COVID hospitals.”

The details of the PPE included three layers of gloves, a coverall, N95 face mask, surgical mask, face shield/goggles, hood with 2 layers of head covering, and a disposable waterproof surgical gown.

China’s approach to preventing transmission from patients and HCW self-inoculation are apparent not only from the scientific literature, Chinese government reports, and public internet. On 2020-04-16, W.H.O. and the Chinese Centers for Disease Control and Prevention co-sponsored a Webinar On The Protection Of Health Workers In Covid-19: Lessons Learned From China12 which showed slides and videos of Chinese HCW using N95 respirators in all hospital situations.

The results discussed above were achieved prior to the development of vaccines. COVID-19 is a workplace preventable disease.

The Evidence is of Strong Certainlty, Not  of Very Low Certainty 

The heart of the matter for occupational and public environments is protecting against inhaling bio-infectious materials exhaled from the lungs of infected people, including the asymptomatic. The China experience may not be familiar to interested parties in Canada and the US., often due to mistrust or sino-phobia. If it had been interested in the ensemble of evidence, W.H.O. could have included the profound literature examining the suppression of the China epidemic in Wuhan, its own experience in the Amoy Gardens Investigation from SARS-1 in 2003, and  it’s sponsoring of a webinar with the Chinese CDC in April 2020.

In consequence, the most important international trigger publication to shift the focus away from ‘droplet precautions’  occurred when Morawska and Milton issued the July 2020 It Is Time to Address Airborne Transmission of Coronavirus Disease 2019 (COVID-19)13 as an appeal to medical community and relevant international bodies. Including the authors, 239 scientists support the Appeal.

While the Morawska-Milton appeal is mainly aimed at public transmission of aerosols, others have  addressed occupation, including prior to the current pandemic. A representative example is that of Jones and Brosseau.14 In 2015, the period between SARS-1 and SARS-CoV-2, they wrote in relation to biological plausibility:

“An infectious aerosol is a collection of pathogen-laden particles in air. Aerosol particles may deposit onto or be inhaled by a susceptible person. Aerosol transmission is biologically plausible when infectious aerosols are generated by or from an infectious person, the pathogen remains viable in the environment for some period of time, and the target tissues in which the pathogen initiates infection are accessible to the aerosol.”

In July 2020 when FFR were not readily available in North America, Brosseau, Rosen, and Harrison15 discussed an occupational hazard assessment tool known as Control Banding for “aerosol-transmissible infectious disease pandemic planning to encourage the use of source and pathway controls before receptor controls (personal protective equipment).” The same group also wrote the Joint Consensus Statement on Addressing the Aerosol Transmission of SARS CoV-2 and Recommendations for Preventing Occupational Exposures16 in which they stated:

“The receptors for SARS-CoV-2 in the body (ACE2) are located throughout the respiratory system. People are capable of inhaling particles over the entire particle size range of aerosols, with larger particles more likely to deposit in the upper respiratory system and smaller particles having a greater probability of penetrating into and depositing in the lungs, bronchioles, and alveoli. “

Jones, et al6 in Two Metres or One: What Is The Evidence for Physical Distancing In Covid-19? pointed out:

“Rules that stipulate a single specific physical distance (1 or 2 metres) between individuals to reduce transmission of SARS-CoV-2, the virus causing covid-19, are based on an outdated, dichotomous notion of respiratory droplet size. This overlooks the physics of respiratory emissions, where droplets of all sizes are trapped and moved by the exhaled moist and hot turbulent gas cloud that keeps them concentrated as it carries them over metres in a few seconds. After the cloud slows sufficiently, ventilation, specific patterns of airflow, and type of activity become important. Viral load of the emitter, duration of exposure, and susceptibility of an individual to infection are also important.”

In summary, the scientific evidence supporting the use of FFR for all HCW entering the rooms of confirmed and suspected COVID-19 positive is robust. It includes biological plausibility, the physics of respiratory emissions in the context of air movement and ventilation in indoor spaces, and PPE evidence accumulated over the course of decades. 

Most importantly, it includes what action-based social research qualifies as the experiential, or in the vernacular, “we learn by doing.” Ignoring the learning demonstrated by the experience of HCW in Wuhan has increased by a long shot the probability of dying and suffering from COVID-19. The evidence is filled with certitude,  and not at all of very low certainty.

Conscious Avoidance of Aerosol Transmission

The words droplet and aerosol do not appear in the Recommendation. In contrast to the mass of accumulated evidence, W.H.O. appears to have simply avoided the topic of aerosol transmission altogether. What would appear to be a strong recommendation for using fit-tested respirators when entering the room of a confirmed or suspected patient is weakened by a presumption of “very low certainty evidence.” With a self-limiting method of tenacity, of clinging to droplet dogma, the set of five W.H.O. References is extremely slim, to the point of ignoring other readily available studies of dubious methodology which would support its claims.

As for Canada, PHAC’s recommendation document contains many of the elements that would allow them to explicitly endorse using an FFR entering any room where there is a patient with suspected or confirmed COVID-19. PHAC explicitly acknowledges aerosol transmission: “These aerosol particles can remain suspended in the air, and be inhaled into the respiratory tract of another person.” 

Risk factors acquisition of healthcare associated SARS-CoV-2 infection include:

  • poor ventilation within the facility
  • healthcare workers’ (HCW) proximity to the patient
  • multi-bed rooms
  • longer durations of exposure to the patient.

PHAC’s recommendations also includes an excellent set of  References, some of which are cited in this report, another being Greenhalgh et al’s Ten scientific reasons in support of airborne transmission of SARS- CoV-217. 

Yet in spite of having searched the literature, the outcome is less than forthcoming. PHAC, like W.H.O., fails to draw the obvious conclusions about aerosol transmission, resulting in non-specific recommendations on respirators. PHAC’s recommendation calls for the use of a “well fitted respirator” along with other personal protective equipment (PPE) during “direct patient care” of patients with confirmed or suspected COVID-19. 

There is no such thing as a “well-fitted” respirator. The message should be a “fit-tested respirator that seals with the skin of the face in accordance with CAN/CSA-Z94.4-18.” This phrase “direct patient care” is a slippery double-entendre, easily defined as limited to clinical care in the AGP setting by those administrators who are opposed to the procurement and use of FFP except in AGP. 

HCW who want to protect themselves will seek a different interpretation and define direct patient care in the broadest terms. These occupational groups include practical nurses, phlebotomy technicians, care aids, housekeeping, food delivery service, social/religious workers, and others regularly enter patients’ rooms as compiled in Table 1 of Jackson et al3.

Then there is the third proviso of wearing a respirator “based on health workers’ values and preferences and on their perception of what offers the highest protection possible to prevent SARS-CoV-2 infection.” Read strictly, this means that in spite of the recommendation to wear fit tested respirators, administrators  or individual HCW can make decisions to not use a respirator if they think a surgical mask is ‘good enough’ because of “low certainty evidence.”. 

This is a most unfortunate state of affairs, no way to break the chains of transmission. In almost countries (including Canada and the United States), employers have the legal obligation to provide controls that prevent occupational disease and to train workers in safe work procedures. Furthermore legislation and regulations have been established for the occupational health and safety committee to assist in developing those safe work procedures. 

Rather than looking for exceptions to safe work procedures based on ‘perceptions’, W.H.O. and PHAC should asking employers and workers to strengthen knowledge on aerosol transmission, the use of respirators according to national standards, and to develop standardized safe work procedures for the entire range of medical applications and post-treatment patient care and recovery. Given the prolonged international health emergency,W.H.O. should be calling for achieving the highest level of protection, not the mediocre. The proviso on workers’ values and perception is a strange beast since W.H.O. does not seem to have identified what those variables might be. This is not an acceptable way to support the health and safety of HCW.

A final critique of W.H.O. and PHAC is required from an action point of view. Neither of these organizations point to well-established international and national standards for respiratory protection and ventilation. Each country and region in the world have such standards. In Canada the occupational respiratory protection standard is Canadian Standards Association CSA Z94.4-18 “Selection, Use and Care of Respirators”. ASHRAE is a global standards organization that provides resources for heating and ventilation, including specific recommendations for COVID-19 prevention. The current Standard is ANSI/ASHRAE Standard 62.1-2019, Ventilation for Acceptable Indoor Air Quality.

Coda

Myths about FFR have long circulated, such as they are less effective and less comfortable than surgical masks, and that the supply of N95 in Canada and the US is limited. By insisting on their rights to a workplace free of SARS-CoV-2, HCW can now point to the WHO Recommendation. This Recommendation, with the exception of provisos, carries a high authority because it does the right thing: a fit-tested FFP worn by workers who understand it use and limitations is one of the best ways for HCW of all job descriptions to protect themselves. With implementation of the Recommendation, HCW can now learn from their own experience about the advantages of FFR, free of administrative strictures based on long-outdated science.

The W.H.O. Recommendations doesn’t go far enough, however. Consider the well-known phenomenon of asymptomatic persons who enter a health care facility be it the testing station, the local laboratory for an INR or other blood & urine sample. Given the evidence of aerosol transmission and recent infectivity rates of the Omicron variant, shouldn’;t every HCW who has patient contact be using a fit tested FFR?

More Resources:

To find a registered or certified Occupational, Environmental, Health, and Safety professional or Scientist in Canada and the USA, contact:

-The Canadian Registration Board of Occupational Hygienists (CRBOH) https://crboh.ca

-American Board of Industrial Hygiene (ABIH) http://abih.org

The professional & scientific associations which have major resources to assist workers and employers protect themselves against SARS-CoV-2 include:

-L’association québécoise pour l’hygiène, la santé et la sécurité du travail https://www.aqhsst.qc.ca

-ACGIH & COVID-19 Resources https://www.acgih.org/covid19/

-AIHA https://www.aiha.org. AIHA maintains a COVID Resources Center 

-AIHA The Role of the Industrial Hygienist in a Pandemic 2nd Edition 

IBEC The Integrated Bioscience and Built Environment Consortium, “We provide digested information, in laypersons’ terms, and easily accessible for everyone.”

-Recent Citizen-Scientist Article: Is It Time to Upgrade from Cloth and Surgical Masks to Respirators? Your Questions Answered by Asadi, MacIntyre, Brosseau, and Greenhalgh

REFERENCES

1. World Health Agency, W.H.O. recommendations on mask use by health workers, in light of the Omicron variant of concern: W.H.O. interim guidelines, 22 December 2021. https://www.who.int/publications/i/item/WHO-2019-nCoV-IPC_Masks-Health_Workers-Omicron_variant-2021.1. Retrieved 2022-01-02.

2. Public Health Agency of Canada. Update with consideration of Omicron – Interim COVID-19 infection prevention and control in the health care setting when COVID-19 is suspected or confirmed– December 23, 2021. Retrieved 2022-01-08 from https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/guidance-documents/omicron-infection-prevention-control-health-care-settings-covid-19-suspected-confirmed.html.

3. Jackson et al, Classification of aerosol-generating procedures: a rapid systematic review. Retrieved 2022-01-08 from https://bmjopenrespres.bmj.com/content/bmjresp/7/1/e000730.full.pdf

4. Public Health Agency of Canada. Routine Practices and Additional Precautions for Preventing the Transmission of Infection in Healthcare Settings. retrieved 2022-01-08 from https://www.canada.ca/en/public-health/services/publications/diseases-conditions/routine-practices-precautions-healthcare-associated-infections/part-a.html

4. Ignatius, T.S., et al. Evidence of Airborne Transmission of the Severe Acute Respiratory Syndrome Virus. N Engl J Med 2004; 350:1731-1739. DOI: 10.1056/NEJMoa032867. Retrieved 2022-01-10.

5. Bourouiba, Turbulent Gas Clouds and Respiratory Pathogen Emissions Potential Implications for Reducing Transmission of COVID-19. JAMA. 2020;323(18):1837-1838. doi:10.1001/jama.2020.4756. Retrieved 2021-12-20.

6. Jones, et al Two metres or one: what is the evidence for physical distancing in covid-19? BMJ 2020;370:m3223. http://dx.doi.org/10.1136/bmj.m3223 Retrieved 2022-01-15.

7. World Health Organization. Weekly epidemiological update on COVID-19 – 6 January 2022. Retrieved on 2022-01-09 from: https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19—6-january-2022.

8. Zhan, M., Qin, M., Xue, X., Zhu, S. Death from Covid-19 of 23 Health Care Workers in China.  https://www.nejm.org/doi/full/10.1056/NEJMc2005696. Published on April 15, 2020, Retrieved 2022-01-12.

9. WHO. Coronavirus disease 2019 (COVID-19) Situation Report – 101 https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200430-sitrep-101-covid-19.pdf?sfvrsn=2ba4e093_2. Retrieved 2022-01-15.

10. Liu, M., Use of personal protective equipment against coronavirus disease 2019 by healthcare professionals in Wuhan, China: cross sectional study. British Medical Journal, http://dx.doi.org/10.1136/bmj.m2195. 2020-08-10. Retrieved 2022-01-12.

11 Zhan, M., et al. Lesson Learned From China Regarding Use Of Personal Protective Equipment. American Journal of Infection Control 48 (2020) 1462-1465. https://doi.org/10.1016/j.ajic.2020.08.007. Retrieved 2022-01-14.

12. Webinar On The Protection Of Health Workers In Covid-19: Lessons Learned From China. The Documentation for this event could not be retrieved from the internet. Having attended the online event, the author can supply the slides upon request.

13. Morawska and Milton. It Is Time to Address Airborne Transmission of Coronavirus Disease 2019 (COVID-19). Clinical Infectious Diseases, Volume 71, Issue 9, 1 November 2020, Pages 2311–2313, https://doi.org/10.1093/cid/ciaa939. Recovered 2022-01-09.

14. Jones, R., Brosseau, L. Aerosol Transmission of Infectious Disease. Journal of Occupational and Environmental Medicine: May 2015 – Volume 57 – Issue 5 – p 501-508 https://pubmed.ncbi.nlm.nih.gov/25816216/. Retrieved 2021-01-14.

15. Brosseau, L., Rosen, J., Harrison, R., Selecting Controls for Minimizing SARS-CoV-2 Aerosol Transmission in Workplaces and Conserving Respiratory Protective Equipment Supplies Annals of Work Exposures and Health, 2021, Vol. 65, No. 1, 53–62. https://doi.org/10.1093/annweh/wxaa083. Retrieved 2022-01-08.

16. Brosseau, L., Mitchell, A., Rosen, J. and Other Volunteers. Joint Consensus Statement on Addressing the Aerosol Transmission of SARS CoV-2 and Recommendations for Preventing Occupational Exposures. AIHA, April 20, 2021 

17. Greenhalgh T, Jimenez JL, Prather KA, et al. Ten scientific reasons in support of airborne transmission of SARS-CoV-2. Lancet. 2021;397:1603- 1605. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00869-2/fulltext. Retrieved 2021-01-14.

 

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