Face Masks MUST Catch Small Droplets
We know that COVID-19 is a disease caused by SARS-CoV-2 coronavirus. What we are still learning is how this virus behaves.
At the beginning of the pandemic, Public Health believed that this virus was transmitted mainly by large droplets expressed from the mouth and nose during loud talking, sneezing and coughing, as well as by contact with infected surfaces.
To prevent large droplet spread, almost anything including a t-shirt over the mouth and nose was thought to provide some significant protection. Further, these droplets, being somewhat heavy, rapidly fall to the ground a few metres from the infected person.
Two key facts have emerged that have changed our thinking about mask wearing:
- It is now clear that in the 2–3 days preceding a symptomatic infection, a person is usually highly contagious. This implies each of us must consider that any apparently well person that we meet may be in the silent stage of the infection and might transmit the virus to us.
- Small droplets are now recognized as an important means of disease transmission. These droplets (aerosols) are produced not only by forceful expiration of air from the mouth or nose but also by simple breathing. They can remain suspended in the air for hours. Unfortunately, small droplets pass through cloth masks with ease.
These facts have led to new mask recommendations by Dr. Tam, Canada's Chief Public Health Officer. She recently announced that Covid-19, face masks for non-health care workers should be three layered with a middle layer of a blown material such as polypropylene. Two layered cloth masks are not adequate for personal protection and for protection of your contacts. The issue is the small respiratory droplets that carry the virus are not effectively trapped by just layers of fine cotton cloth. A middle layer of nonwoven material placed between the mask’s inner and outer layers is effective at catching most of these Covid-19 bearing droplets.
This small droplet concept makes good sense as we know that there is increased chance of virus transmission in indoor spaces especially with poor ventilation. The fine droplets do not fall to the ground but continue to circulate in the air for hours. Likely the concentration of them increases the longer an infected person is in the enclosed space. This fact helps to explain the Covid-19 outbreaks that occur in indoor places where people congregate - including places of worship, bars, restaurants, cruise ships, and small social groups.