Cloth Masks Can Help Stop Spread of COVID-19
(Reuters Health) – Cloth masks may help prevent transmission of the SARS-CoV-2 virus by at least partially blocking droplets expelled by people when they speak, cough and sneeze, researchers say.
While the weave of cloth masks may not be tight enough to block individual virus particles, most virions spread in aerosols (smaller than 5 micrometers) or larger droplets, and there is ample evidence that the masks can prevent such droplets from getting into the air or onto surfaces, the authors argue in an opinion piece published in the Annals of Internal Medicine
Dr. Catherine Clase, an associate professor of medicine at McMaster University and a nephrologist at St. Joseph’s Hamilton Healthcare, in Ontario, Canada, and her colleagues reviewed the available literature on cloth masks. While there is no direct evidence yet that cloth masks can reduce SARS-CoV-2 transmission, they write, the collective evidence indicating that mask wearing by infected people reduces contamination is convincing and should inform policy.
There was also evidence, though not as strong, that cloth masks might protect wearers as well, the authors found.
“We found some cloth masks, particularly when the cloth is in layers, can be remarkably effective in reducing contamination of the environment,” Dr. Clase told Reuters Health. “We looked at studies that tested masks to see if mouth germs end up in the air. So, if I know they can decrease contamination, maybe I am going to altruistically wear one.”
In one study, researchers found that “filtration efficiency for single layers of different types of cotton cloth in a bioaerosol (0.2 micrometer) experiment was between 43% and 94%, compared with 98% to 99% for fabric from disposable medical masks,” Dr. Clase and her coauthors write.
Much of the research reviewed by Dr. Clase and her colleagues was decades old. Yet, they write, the results are highly relevant today. The data don’t just show that masks can prevent outward transmission of pathogens. In animal experiments, researchers found that cloth masks prevented the inward transmission of aerosolized tubercle bacilli, Dr. Clase and colleagues note.
“The evidence we found doesn’t say all particles are going to be stopped,” Dr. Clase said. “But some will be stopped. Most of the time you’re not going to be exposed to viruses floating freely in the air, but rather, to virus in droplets or aerosols. If you can decrease the amount that’s in the environment that’s a good thing.”
While the evidence shows that masks can help, Dr. Clase cautioned, “they are no substitute for social distancing and handwashing but should be used along with those measures.”
Dr. Clase also advises people to make sure they wash their cloth masks after use and take care when they remove them. “If you think about the fact that you are using it to protect yourself from particles in the air, those particles are going to end up embedded in the outer surface,” she said. “When you take a mask off, you want to remove the bottom strap first and then the top. You want to fold the inside surfaces together and put it in a paper bag until you can wash it.”
Dr. Clase also cautioned against mask wearing in children under 2 years of age and in people with breathing problems.
Supratik Guha, whose recent experimental study showed that layered cloth masks can block a large proportion of small-sized particles, welcomed the new article.
“I have been stressing that simple reasoning and evidence indicates that the use of a decent cloth mask in indoor or busy public places will reduce infection transmission,” said Guha, a professor at the Pritzker School of Molecular Engineering at the University of Chicago. “If most of the population practices this, the multiplicative benefits can be enormous in reducing overall infection rates within a community.”
“It is a simple, uncomplicated practice that can have a decisive impact – there is no magic or fuzzy science here,” Guha said in an email. “This paper gives a clear-eyed assessment of the scientific data available so far on cloth masks, and supports a conclusion such as this.”
“An interesting point is that as you increase the layers you decrease breathability,” Dr. Clase said. “Three layers is better than two and four is maybe better yet, but as you increase the number of layers, it becomes harder to breathe through the material – which means people may be less likely to wear them and keep them on.”
SOURCE: https://bit.ly/2M6yS0G Annals of Internal Medicine, online May 22, 2020. (Editing by Christine Soares)