Studies Track Infections to Measure Mask Effectiveness

S. Shaefer Spires, MD; Valeria Fabre, MD


August 14, 2020

Editorial Collaboration

Medscape &

Do masking and other mitigation strategies protect healthcare workers from occupational transmission of SARS-CoV-2?

A study by Contejean and colleagues looked at positivity rates in healthcare workers associated with a bundle of interventions that included universal masking, hand hygiene emphasis, and use of recommended personal protective equipment (PPE) (medical masking, gowns, gloves, eye protection, and N95 masks for aerosol-generating procedures).

The study investigators tested all symptomatic healthcare workers for SARS-CoV-2 and found a 2.8% positivity rate overall, with 3.2% in the adult hospital and 2.3% in the children's hospital. As compliance with universal masking and PPE use improved and close contact with unmasked employees was reduced, the rate of cases in healthcare workers decreased. Most of the COVID-positive healthcare workers (70%) were in direct patient-facing roles, and 78% were outside dedicated COVID-19 units. Major limitations of the study were the lack of a control group and that it only included symptomatic participants to compare behaviors and exposures.

In another study, Wang and colleagues reported findings of SARS-CoV-2 positivity in healthcare workers across a large health system in the northeast United States before and after implementation of universal masking of all healthcare workers and patients.

Of 9850 tested healthcare workers, 1271 (12.9%) were positive. During the preintervention period, the positivity rate among healthcare workers went from 0 to 21.32%, or 1.16% per day, with a case doubling time of 3.6 days. During the intervention period, positivity rate decreased linearly from 14.65% to 11.46% (mean decline of 0.49% per day), with a net slope change of 1.65% more decline per day compared with the preintervention period. These findings could be confounded by other interventions inside and outside the healthcare system, such as reductions in elective procedures, social distancing, and increased masking in public.

A third study, by Seidelman and colleagues, was unique in that the authors attempted to classify SARS-CoV-2 infection as community-acquired, healthcare-acquired, or of unknown acquisition on the basis of phone interviews with affected healthcare workers. Incidence rates of COVID-19 acquisition among healthcare workers before and after universal masking were compared using negative binomial regression; 38% of cases were community-acquired, 22% were healthcare-associated, and 40% did not have a clear source of acquisition. Most of the healthcare workers did not work on COVID units.

Of the healthcare-associated cases, 70% were related to unmasked exposure to another healthcare worker and 30% were thought to be secondary to direct care of COVID-positive patients. One week after the implementation of universal masking, there was a significant decrease in the cumulative incidence rate of healthcare-acquired SARS-CoV-2 infections among healthcare workers.


These studies demonstrate that universal masking is associated with a significantly lower rate of COVID transmission. Notably, a vast majority of occupationally acquired cases were found to be related to exposures without adequate PPE, either from another coworker or a patient. It is also notable that two of these studies demonstrated a decrease in the rate of SARS-CoV-2 acquisition among healthcare workers in the setting of increasing cases in their respective communities.

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