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OHSU evidence review examines role of masks in containing spread of COVID-19

Author says even a small effect can have a big impact on reducing exponential spread of novel coronavirus
people walking in public, wearing protective masks
A new review finds facial coverings helped decrease the spread of another coronavirus that causes severe acute respiratory syndrome, or SARS. In addition, the researchers found no evidence of serious harm from wearing masks. (Getty Images)

Facial coverings appear to decrease the risk of spreading respiratory illness in public, according to a new evidence review by researchers at Oregon Health & Science University.

Although researchers found no definitive clinical studies evaluating the effectiveness of masks to prevent the spread of the novel coronavirus that causes COVID-19, they did find evidence that facial coverings were associated with decreasing the spread of another coronavirus that causes severe acute respiratory syndrome, or SARS. In addition, the researchers found no evidence of serious harm from wearing masks.

The review’s lead author said the apparent contagiousness of the novel coronavirus suggests it’s reasonable for public health officials to ask people to wear facial coverings in public settings to reduce spreading the virus when there is widespread community transmission.

Roger Chou, M.D.
Roger Chou, M.D.

“Even if masks are only modestly effective, it creates a big effect down the road because the virus spreads exponentially,” said Roger Chou, M.D., director of the Pacific Northwest Evidence-based Research Center at OHSU. “Even a small effect on wearing masks in public could have a big impact on community spread down the road.”

The review was published today in the journal Annals of Internal Medicine.

The review included 39 studies previously conducted examining the effectiveness of masks in preventing the spread of respiratory infections in community settings and in health care. It formed the basis of a series of practice points issued by the American College of Physicians.

Case counts are rising in many areas across the country, as businesses reopen and economic activity resumes. There is no vaccine to prevent the disease caused by the novel coronavirus and still no proven treatment for people who become critically ill.

The virus spreads exponentially in the absence of measures to contain it.

“It’s not just whether you’re wearing a mask,” said Chou, who also is a professor of medicine (general internal medicine and geriatrics) and medical informatics and clinical epidemiology in the OHSU School of Medicine. “It’s also how good are you about physical distancing, how good you are at handwashing, and how exposed you are to people who are infected.”

Even though the disease has killed 120,000 people in the U.S. alone, some people have symptoms so mild they don’t realize they’re carrying the virus. Facial coverings may be most worthwhile in preventing those people from unwittingly spreading the virus to others by the simple act of talking or breathing.

“The goal with masks is to put up another hurdle for the virus,” said John Townes, M.D., medical director of Infection Prevention and Control at OHSU who wasn’t involved in the review. “We know from a variety of experimental studies that talking – regular, normal speech – can release small droplets of respiratory secretions into the air that may be breathed in by someone else, or may contaminate surrounding surfaces.

“The more you talk, and the louder you talk, the greater the number of respiratory droplets you will produce. Common sense would tell you that if you cover your nose and mouth, fewer of these particles will spread around you.”

The review also found no evidence of serious harm from wearing a mask – a point backed up by an OHSU pulmonologist who wasn’t involved in the study.

“Masks can have some occasional adverse effects like discomfort, skin irritation or shortness of breath, especially for people with chronic lung or heart disease,” said Gopal Allada, M.D., associate professor of medicine (pulmonary and critical care medicine) in the OHSU School of Medicine “However, on balance, the benefits in preventing virus transmission far outweigh the potential risks of wearing a mask.”

Funding for the study was supported under Contract No. HHSA290201500009I, Task Order 75Q80119F32021, from the Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services.

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