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Transmission Through Inhalation
The advice provided by international organizations is converging towards a model of COVID-19 transmission through inhalation of respiratory particles. In September 2020, Canada’s Chief Science Advisor Expert Panel on COVID-19 stated that “[c]lose and prolonged contact is the most common route of SARS-CoV-2 transmission, which includes short-range inhalable particle transmission.” 1. In November 2020, the Public Health Agency of Canada reported that “[i]nfectious droplets or aerosols may come into direct contact with the mucous membranes of another person’s nose, mouth or eyes, or they may be inhaled into their nose, mouth, airways and lungs.” 2. In December 2020, the World Health Organization reported that “[c]lose-range contact (typically within 1 metre) can result in inhalation of, or inoculation with, the virus through the mouth, nose or eyes.” 3.
The Institut national de santé publique du Québec (INSPQ) also recognized, in a notice published on January 8, 2021, that transmission depends on a continuum of particles of different sizes 4. Given this, transmission from close contact with an infected person could be as much the result of inhalation of the particles as of their projection onto the mucous membranes of the eyes, nose and mouth 5. Acknowledgement of inhalation as a transmission mode is important when assessing the risk of exposure to SARS-CoV-2 in healthcare settings 6. SARS-CoV-2 is a recognized danger and constitutes a genuine risk for healthcare workers. This fact should inform the measures that must be implemented to properly control this risk. The recent arrival of new variants of the virus also justifies increased vigilance in this regard.
Some field data gathered since the beginning of the pandemic show that healthcare workers are overrepresented in the number of confirmed COVID-19 cases. In Québec, the results of an epidemiological survey revealed an approximately 10 times higher risk of contracting the disease than that estimated for the rest of the population 7. The report notes that patient attendants, nurses and nursing assistants alone accounted for 70% of all cases in care settings. The provision of close-contact care and exposure duration are risk factors to consider. Infection outbreaks among healthcare workers continued at a rate of 240 to 250 new cases per day at the end of 2020 8. By then, almost 10% of healthcare workers had contracted COVID-19. This high prevalence reveals shortcomings in the measures currently in place to control healthcare workers’ exposure.
Controlling Exposure (Respiratory Protection)
Medical masks are not respirators and do not protect workers from inhalable particles. Regardless of the level of protection of the medical mask (1, 2 or 3), even if the worker tries to adjust it properly, it is impossible to avoid leaks and to prevent inhalation of particles 9 10 11 12. In that context, only a respirator provides adequate protection. In fact, a significant number of Canadian and international organizations have made recommendations for the expanded use of respirators in this pandemic 13 14 15 16 19. Additionally, in order to optimize respirator performance, the implementation of a respiratory protection program, including training and fit testing, is essential, as stipulated in the Guide des appareils de protection respiratoire utilisés au Québec and the CSA Z94.4 standard, Selection, Use and Care of Respirators 17 18.
Assessment of Healthcare Workers’ Risk of Exposure to Inhalable Viral Particles and Recommendation
The IRSST believes that any healthcare workers who work with patients suspected or confirmed as having COVID-19 are at risk of exposure to SARS-CoV-2. Therefore, a number of parameters must be considered when assessing risk, including the following:
- The worker’s proximity to the source (infected patient);
- The number and duration of contacts with patients suspected or confirmed as having COVID-19;
- Air treatment in the context of sustained presence of SARS-CoV-2;
- Continuous wearing of medical masks by patients during their stay in a care setting;
- The level of community transmission;
- The number and duration of contacts with undiagnosed patients.
To adequately protect healthcare workers, the IRSST recommends that respirators should be worn in areas where there is a risk of exposure to SARS-CoV-2.
1. Chief Science Advisor Expert Panel on COVID-19. (2020). The Role of Bioaerosols and Indoor Ventilation in COVID-19 Transmission. http://science.gc.ca/eic/site/063.nsf/eng/h_98176.html
2. Public Health Agency of Canada. (2020). COVID-19: Main modes of transmission. https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/health-professionals/main-modes-transmission.html
3. World Health Organization. (2020). Mask use in the context of COVID19: Interim guidance. https://www.who.int/publications/i/item/advice-on-the-use-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreak
4. Anctil, G., Caron, S. Charest, J., Irace-Cima, A., Gilca, V., Sauvageau, C., . . . Perron, S. (2020). Transmission du SRAS-CoV-2: constats et proposition de terminologie. https://www.inspq.qc.ca/sites/default/files/publications/3099-transmission-sras-cov-2-constats-terminologie-covid19.pdf
5. Milton, D. K. (2020). A Rosetta Stone for Understanding Infectious Drops and Aerosols. Journal of the Pediatric Infectious Diseases Society, 9(4), 413–415. https://doi.org/10.1093/jpids/piaa079
6. Marchand, G. and Debia, M. (2021). COVID-19 : transmission du SARS-CoV-2 et protection respiratoire pour les travailleurs de la santé. Travail et santé, 36(3), S4-S5.
7. De Serres, G., Carazo, S., Lorcy, A., Villeneuve, J., Laliberté, D., Martin, R., … Dionne, M. (2020). Enquête épidémiologique sur les travailleurs de la santé atteints par la COVID-19 au printemps 2020. https://www.inspq.qc.ca/publications/3061-enquete-epidemiologique-travailleurs-sante-covid19
8. Paré, I. and Cousineau, M.-E. (December 18, 2020). Près de 30 000 cas de COVID-19 parmi les employés du réseau de la santé. Le Devoir. https://www.ledevoir.com/societe/sante/591993/pres-de-30-000-cas-parmi-les-employes-du-reseau
9. Oberg, T. and Brosseau, L. M. (2008). Surgical mask filter and fit performance. American Journal of Infection Control, 36(4), 276–282 https://www.ajicjournal.org/article/S0196-6553(07)00774-2/fulltext
10. Karuppasamy, K. and Obuchowski, N. (2021). Comparison of Fit for Sealed and Loose-Fitting Surgical Masks and N95 Filtering Facepiece Respirators. Annals of Work Exposures and Health. https://doi.org/10.1093/annweh/wxaa125
11. Vuma, C. D., Manganyi, J., Wilson, K. and Rees, D. (2019). The Effect on Fit of Multiple Consecutive Donning and Doffing of N95 Filtering Facepiece Respirators. Annals of Work Exposures and Health 63(8), 930–936. https://doi.org/10.1093/annweh/wxz060
12. Girard, M.-A. (director). Je l’ai testé : bien ajuster son masque. https://savoir.media/facteurs-de-risque/clip/je-lai-teste-bien-ajuster-son-masque
13. Centers for Disease Control and Prevention (2020). Personal Protective Equipment: Questions and Answers. https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirator-use-faq.html
14. European Centre for Disease Prevention and Control. (2020). Infection prevention and control and preparedness for COVID-19 in healthcare settings (5th update). https://www.ecdc.europa.eu/sites/default/files/documents/Infection-prevention-and-control-in-healthcare-settings-COVID-19_5th_update.pdf
15. Public Health Agency of Canada. (2021). Infection prevention and control for COVID-19: Interim guidance for acute healthcare settings. https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/health-professionals/infection-prevention-control-covid-19-second-interim-guidance.html#a8.1.1
16. Shared Health Manitoba. (2021). Personal protective equipment (PPE) resources. https://sharedhealthmb.ca/covid19/providers/ppe-resources/
17. CSA Group. (2018). Selection, Use, and Care of Respirators (CSA standard Z94.4-18). Toronto, ON: CSA.
18. Commission des normes, de l’équité, de la santé et de la sécurité du travail. (n.d.). Appareils de protection respiratoire : guide réglementaire. https://reptox.cnesst.gouv.qc.ca/apruq/guide-reglementaire/Pages/000-table-des-matieres.aspx
19. Centers for Disease Control and Prevention (2020). Summary for Healthcare Facilities: Strategies for Optimizing the Supply of N95 Respirators during Shortages. https://www.cdc.gov/coronavirus/2019-ncov/hcp/checklist-n95-strategy.html