By Gary Evans, Medical Writer

Public health officials are citing a hospital study on the efficacy of mask use among healthcare workers and patients in preventing COVID-19 transmission to support recommendations recommendations for universal masking in the community.

“While we studied healthcare workers, the results also apply to other situations in which social distancing is not possible,” says lead author Deepak Bhatt, MD, MPH, of Brigham and Women’s Hospital in Boston. “For those who have been waiting for data before adopting the practice, this paper makes it clear: Masks work.”

The study was conducted at 12 hospitals in the Mass General Brigham (MGB) system. In March 2020, MGB began SARS-CoV-2 testing of symptomatic healthcare workers and universal masking of all staff and patients. Hospitals provided surgical masks to patients.1

Using electronic medical records, the researchers identified healthcare workers who cared for patients with COVID-19 between March 1 and April 30. The study was divided into several phases, including a preintervention period before implementation of universal masking of staff (March 1-24), a transition period until implementation of universal masking of patients (March 25-April 5), a period to watch for manifestation of symptoms (April 6-10), and an intervention period (April 11-30). Overall, 9,850 healthcare workers were tested and 12.9% were positive for COVID-19. These included 7.4% of physicians or trainees, 26.5% of nurses or physician assistants, 17.8% technologists or nursing support, and 48.3% of other.

“During the preintervention period, the SARS-CoV-2 positivity rate increased exponentially from 0% to 21.3%, with a weighted mean increase of 1.1% per day and a case doubling time of 3.6 days,” the authors reported. “During the intervention period, the positivity rate decreased linearly from 14.6% to 11.4%, with a weighted mean decline of 0.49% per day. Universal masking at MGB was associated with a significantly lower rate of SARS-CoV-2 positivity among healthcare workers.”

Although the results could be confounded by other variables to some degree, the number of COVID-19 cases continued to increase in Massachusetts over the study period. That suggests the reduction in COVID-19 in healthcare workers occurred before the decrease in the community, the authors noted.

Hospital staff wore surgical masks in general, and N95 respirators when caring for known or suspected COVID-19 patients. “We did not assess compliance in our study, though what I saw on the wards was 100% compliance,” Bhatt notes. The results can “absolutely” be extrapolated to other hospitals who adopt universal masking of staff and patients, he adds.

Community Transmission

Universal masking in communities could protect healthcare workers, who in some areas may face as much COVID-19 risk away from work as on duty.

“The majority of our [staff exposures] are from the community,” says JoAnn Shea, ARNP, MS, COHN-S, director of employee health and wellness at Tampa (FL) General Hospital.

Although Florida in general has been hard-hit by the virus, Shea said staff infections started out somewhat sporadically.

“I think we had 18 people in March, nine in April, and six in May,” she says. “Then, we went up to 208 [employees] who had it in June when they opened up the state. They all got it in the community.”

Employee health has set up a 24-hour COVID-19 hotline to answer worker questions about travel and exposures to friends or family with the virus. While most cases are acquired in the community, there have been some incidents suggestive of occupational infection, Shea says.

“All of our [employees] have to wear a mask all day, but we have had some clusters where we have three to six team members get COVID on a unit,” she says. “When we look at their histories, there was no community contact. [We found] that they may have had a patient who kept taking their mask off and coughing.”

This could have contaminated the patient environment and surfaces, which workers may have touched before bringing hands to their face. Because of this cluster, all healthcare workers are required to wear eye protection for patient care.

“In most people [the infection] is self-limiting, though we have had some employees with more severe illness,” she says. “The younger people hardly have symptoms. We allow them back after 10 days if they have no symptoms, and 11 days if they had a fever. We are finding with the ones who are sick, we usually don’t get them back until day 14 or 15. We don’t want to clear anyone with a productive cough or shortness of breath.”

In a recent revision, the Centers for Disease Control and Prevention (CDC) is emphasizing monitoring such symptoms instead of using return-to-work policies based on SARS-CoV-2 testing. As of July 17, the CDC recommends that “except for rare situations, a test-based strategy is no longer recommended to determine when to allow healthcare personnel (HCP) to return to work. [I]n the majority of cases, it results in excluding from work HCP who continue to shed detectable SARS-CoV-2 RNA but are no longer infectious.”2

In another guidance revision, the CDC recommended extending work exclusions to 20 days after symptom onset for healthcare staff with severe to critical illness or who are severely immunocompromised. If immunocompromised HCWs are asymptomatic, they should be excluded from work 20 days after their initial positive test.

Other modified symptom-based criteria include a change from “at least 72 hours” to “at least 24 hours” after the last fever without the use of fever-reducing medications, the CDC reported.

“Decisions about return to work for HCP with SARS-CoV-2 infection should be made in the context of local circumstances. In general, a symptom-based strategy should be used,” the CDC advised.

Local circumstances have gotten worse for Hamad Husainy, DO, FACEP, an emergency physician at Helen Keller Hospital in Sheffield, AL. Community spread is putting pressure on hospitals, increasing the exposure risk to workers as patients come in.

“The cases have definitely increased. Our local hospitals are full, and COVID units have expanded,” he says. “We are probably seeing four or five cases requiring hospitalization a day, with another 20 to 25 cases not requiring hospitalization.”

As this report was filed, Alabama had enacted a public mask requirement. (More information is available at: The measure should help, as there remains resistance to masking in some areas of the state, Husainy says.

“It will either improve compliance or people that really feel compelled not to wear a mask will just stay in,” he says. “I would say the majority of this [transmission] is in the public. I happen to live in an area where compliance is not good. Whether it is political, constitutional, or whatever the rationale, it is preventing people from wearing [masks]. There is a lack of compliance in the community.”

The hospital has a thin margin of frontline staff, meaning that if someone gets sick, the workload increases for other emergency department nurses and physicians, Husainy says.

“We may not be New York or Houston, but we are dealing with a lot of uncertainty,” he says. “Increased work requirements can bring people to a point where they are depleted of wellness.”

With this same scenario playing out over much of the country, the CDC is trying to convey the message that universal masking in the community can prevent transmission.

“I really believe if the American public all embraced masking and we really did it rigorously, in the next four, six, or eight weeks we could bring this epidemic under control,” CDC Director Robert Redfield, MD, said in a recent interview.

There was a time when such an urgent plea by the most respected public health agency in the world would translate to broad action. Now, it is an open question, given the futility and infighting at the highest levels of the pandemic response in the United States. The CDC cited an accumulating body of evidence in a recently published editorial that the “time is now” for all to wear masks to blunt the spread of COVID-19.3

“When asked to wear face coverings, many people think in terms of personal protection,” the CDC stated. “But face coverings are also widely and routinely used as source control. For instance, if given the choice between having surgery performed by a team not wearing some covering over their mouths and noses vs. a team that does, almost all patients would reject the former. This option seems absurd because it is known that use of face coverings under these circumstances reduces the risk of surgical-site infection caused by microbes generated during the surgical team’s conversations or breathing. Face coverings do the same in blocking transmission of SARS-CoV-2.”

Universal masking could lower asymptomatic spread, which may be a “critical driver” of ongoing transmission. The CDC cited the efficacy of this approach demonstrated in public, household, and hospital settings, but concedes it would be exceedingly difficult to conduct a randomized trial of mask effectiveness in the community.

“In the absence of such data, it has been persuasively argued the precautionary principle be applied to promote community masking because there is little to lose and potentially much to be gained,” the CDC stated. “Like herd immunity with vaccines, the more individuals wear cloth face coverings in public places where they may be close together, the more the entire community is protected. Community-level protection afforded by use of cloth face coverings can reduce the number of new infections and facilitate cautious easing of more societally disruptive community interventions such as stay-at-home orders and business closings.”

In addition to citing Bhatt’s study in Boston, the CDC reported wearing masks prevented the spread of infection from two beauticians to their customers in Missouri.

“Among 139 clients exposed to two symptomatic hairstylists with confirmed COVID-19 while both the stylists and the clients wore face masks, no symptomatic secondary cases were reported,” the CDC concluded. “Among 67 clients tested for SARS-CoV-2, all test results were negative. Adherence to the community’s and company’s face-covering policy likely mitigated spread of SARS-CoV-2.”4

One stylist developed respiratory symptoms but continued to see clients for eight days. The other, who apparently became infected from her co-worker, also developed respiratory symptoms and continued to see clients for four days. With clients wearing masks to comply with a local ordinance, no transmission occurred.


  1. Wang X, Ferro EG, Zhou G, et al. Association between universal masking in a health care system and SARS-CoV-2 positivity among health care workers. JAMA 2020; Jul 14;e2012897. doi: 10.1001/jama.2020.12897. [Epub ahead of print].
  2. Centers for Disease Control and Prevention. Criteria for return to work for healthcare personnel with SARS-CoV-2 infection (interim guidance). Updated July 17, 2020.
  3. Brooks JT, Butler JC, Redfield RR. Universal masking to prevent SARS-CoV-2 transmission-The time is now. JAMA 2020; Jul 14. doi: 10.1001/jama.2020.13107. [Epub ahead of print].
  4. Hendrix MJ, Walde C, Findley K, et al. Absence of apparent transmission of SARS-CoV-2 from two stylists after exposure at a hair salon with a universal face covering policy — Springfield, Missouri, May 2020. MMWR Morb Mortal Wkly Rep 2020;69:930-932.