COVID-19 (Coronavirus Disease 2019), evolving from China in December 2019, has spread almost all over the world. This disease is caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), which transfers from one person to another through respiratory droplets and aerosols created by expiratory activities. The transmission of coronaviruses occurs when the respiratory droplets and aerosols emitted from an infected person reach the nose, mouth, or eyes of another person [1,2]. Coronaviruses can transfer directly through human-to-human contact (e.g., handshaking, hugging), indirectly through touching materials or objects that carry infection (e.g., doorknob, handrail, paper tissue), and via airborne route [3]. The transmission of coronaviruses can be prevented using highly efficient face masks. N95 respirator masks are being used as “high-efficiency masks” in the current pandemic situation. But are they sufficient for protection against coronaviruses?

As per the guideline of WHO, health-care professionals must wear masks when caring for patients with airborne infections, or when executing bronchoscopies or similar tests for their own protection; in such cases, “high-efficiency masks” are recommended [4]. In battling against SARS-CoV-2, health-care staff are using N95 respirator masks. But N95 respirator masks may not certainly provide adequate protection against coronaviruses, which are significantly smaller than 300nm (0.3µm) inert particles used in the acceptance test of this type of masks [5]. The diametrical size of viruses varies in the range of 20–300 nm (0.02–0.3 µm). SARS-CoV-1 ranges from 75 nm (0.075 µm) to 160 nm (0.160 µm) in diameter [6] whereas SARS-CoV-2 varies from 65 nm (0.065 µm) to 125 nm (0.125 µm) [7]. Thus, the penetration of coronaviruses through N95 respirator masks could be more than 5% due to their very small size. The research results of Bałazy et al. [5] showed that N95 respirator masks will be adequate against the particles ≥ 300 nm in diameter; but they may not give proper protection with 95% threshold value for the nano-size virus particles; in their study, the penetration of small virus particles less than 80 nm was 2.25–3.25% at a lower inhalation rate of 30 L/min whereas it was 4.25–5.75% at a higher inhalation rate of 85 L/min. Furthermore, the wearer may not get the desired level of protection unless the respirator is fitted well with the face without any leakage [8]. All these mean that the 95% protection level of N95 masks is not guaranteed for the health-care professionals giving treatment to COVID-19 patients.

In fine, N95 respirator masks are not 95% effective in preventing virus particles during inhalation. The nano-size coronavirus could penetrate N95 respirator masks by more than 5%. A 5% penetration may not be very harmful in the case of inert particles. Conversely, a very little penetration of coronaviruses would be enough to cause substantial damage. This is because sometimes a single virus particle can cause infection [6]. Therefore, relying solely on N95 respirator masks strategically will not be sufficient to prevent coronaviruses from entering the respiratory tract. A better option could be to use it as an element in the practice of multi-level protection; for example, a face shield on top of a google for eye protection and an N95 respirator mask alone or covered by a surgical mask for nose and mouth protection. Alternatively, full-facepiece air-purifying respirators (APRs) and powered air-purifying respirators (PAPRs) can be used by the health-care personnel for protection against COVID-19 [9,10]. APRs and PAPRs simultaneously cover eyes, nose, and mouth. They are reusable and can be used more than once following the guidelines for cleaning, sanitizing, and/or disinfecting [11,12]. Both APRs and PAPRs are used with disposable filters and most common filters are N95 and P100. But N95 filters will not give more than 95% protection as discussed earlier. High-level respiratory protection is expected to achieve by P100 filters. A P100 filter is effective against all particulate aerosols and 99.97% efficient against 0.3µm particles [13]. It means that the penetration of 0.3µm particles through a P100 filter should not be more than 0.03%. Therefore, APRs and PAPRs with P100 filters would likely give better protection than N95 respirator masks against COVID-19. The assigned protection factor is 50 and 1000 for full-facepiece APRs and PAPRs, respectively, whereas it is only 10 for N95 respirator masks [13-15].

List of References:

[1] Mount Sinai Hospital. FAQ: Methods of Disease Transmission. Department of Microbiology, Mount Sinai Hospital: Toronto, Ontario, Canada. Retrieved on March 31, 2020. Available online: https://eportal.mountsinai.ca/Microbiology/faq/transmission.shtml.
[2] World Health Organization (WHO). Pass the Message: Five Steps to Kicking out Coronavirus. WHO: Geneva, Switzerland; March 23, 2020. Retrieved on March 24, 2020. Available online: https://www.who.int/news-room/detail/23-03-2020-pass-the-message-five-steps-to-kicking-out-coronavirus.
[3] Asadi, S.; Bouvier, N.; Wexler, A.S.; Ristenpart, W.D. The coronavirus pandemic and aerosols: Does COVID-19 transmit via expiratory particles? Aerosol Science and Technology 2020, 54(6), 635-638.
[4] World Health Organization (WHO). Prevention of Hospital-Acquired Infections: A Practical Guide; Second Edition, WHO/CDS/CSR/EPH/2002.12; Ducel, G., Fabry, J., Nicolle, L., Eds.; WHO: Geneva, Switzerland, 2002. Retrieved on March 26, 2020. Available online: https://www.who.int/csr/resources/publications/whocdscsreph200212.pdf.
[5] Bałazy, N.; Toivola, M.; Adhikari, A.; Sivasubramani, S.K.; Reponen, T.; Grinshpun, S.A. Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks? American Journal of Infection Control 2006, 34(2), 51-57.
[6] Morawska, L. Droplet fate in indoor environments, or can we prevent the spread of infection. Indoor Air 2006, 16(5), 335-347.
[7] Shereen, M.A.; Khan, S.; Kazmi, A.; Bashir, N.; Siddique, R. COVID-19 infection: Origin, transmission, and characteristics of human coronaviruses. Journal of Advanced Research 2020, 24, 91-98.
[8] Coffey, C.C; Lawrence, R.B.; Campbell, D.L.; Zhuang, Z.; Calvert, C.A.; Jensen, P.A. Fitting characteristics of eighteen N95 filtering-facepiece respirators. Journal of Occupational and Environmental Hygiene 2004, 1(4), 262-271.
[9] FDA (Food and Drug Administration). N95 Respirators and Surgical Masks (Face Masks). U.S. Food and Drug Administration: Maryland, USA. Retrieved on March 28, 2020. Available online: https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/n95-respirators-and-surgical-masks-face-masks#s2.
[10] CDC (Centre for Disease Control and Prevention). Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings. CDC: Atlanta, Georgia, USA. Retrieved on May 13, 2020. Available online: https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control-recommendations.html?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fcoronavirus%2F2019-ncov%2Finfection-control%2Fcontrol-recommendations.html.
[11] 3M (Minnesota Mining and Manufacturing) Canada. How to Inspect, Clean and Store 3M™ Reusable Respirators. 3M: London, Canada: Retrieved on May 14, 2020. Available online: file:///F:/COVID19%20Paper%201/Literature/How-to-Inspect-Clean-and-Store-3M-Reusable-Respirators.pdf
[12] 3M (Minnesota Mining and Manufacturing) United States. Guidelines for Cleaning and Disinfecting the 3M™ Powered Air Purifying Respirator (PAPR) TR-300 Assembly. 3M: Minneapolis USA; June 17, 2016. Retrieved on May 14, 2020. Available online: https://www.3m.com/3M/en_US/worker-health-safety-us/all-stories/full-story-detail/?storyid=e706502a-0c64-4783-9f00-6248893619a1.
[13] The National Academies of Science, Engineering and Medicine. Reusable Elastomeric Respirators in Health Care. Clever, L.H., Rogers, B.M.E., Yost, O.C., Liverman, C.T., Eds.; The National Academies Press: Washington D.C., USA, 2019.
[14] Rengasamy, S.; Walbert, G.; Newcomb, W.; Coffey, C.; Wassell, J.T.; Szalajda. J. Protection factor for N95 filtering facepiece respirators exposed to laboratory aerosols containing different concentrations of nanoparticles. The Annals of Occupational Hygiene 2015, 59(3), 373–381.
[15] Vo, E.; Zhuang, Z.; Horvatin, M.; 2, Liu, Y.; He, X.; Rengasamy, S. Respirator performance against nanoparticles under simulated workplace activities. The Annals of Occupational Hygiene 2015, 59(8), 1012–1021.

Md. Safiuddin
Professor
George Brown College, Casa Loma Campus
146 Kendal Avenue, C Building, Room C303
Toronto, Ontario, Canada M5T 2T9
Adjunct Professor, Department of Civil Engineering
Ryerson University, Toronto, Ontario, Canada M5B 2K3
College Website: https://www.georgebrown.ca/facultybios/Md.-Safiuddin.aspx
Google Scholar: https://scholar.google.ca/citations?user=WboBlwQAAAAJ&hl=en
Research Gate: https://www.researchgate.net/profile/Md_Safiuddin