Md. Safiuddin:
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 Coronavirus2), which transfers from one person to another through respiratory droplets and aerosols created by expiratory activities. The transmission of coronaviruses occurs when the respiratory dropletsand aerosols emitted from an infected person reach the nose, mouth, or eyes of another person. 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. 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.
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. The diametrical size of viruses varies in the range of 20-300 nm (0.02-0.3 µm). SARS-CoV-1ranges from 75 nm (0.075µm) to 160 nm (0.160 µm) in diameter whereas SARS-CoV-2 varies from 65 nm (0.065 µm) to 125 nm (0.125 µm). Thus, the penetration of coronaviruses through N95 respirator masks could be more than 5% due to their very small size. The research results of Balazy 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. 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. 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-face piece air-purifying respirators(APRs) and powered air-purifying respirators (PAPRs) can be used by the health-care personnel for protection against COVID-19.
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. 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. 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.
(Md. Safiuddin, Professor, George Brown College, Toronto, Canada).
