Protecting our HEROES (HEalth caRe wOrkErS): Evidence Supporting Universal Masking

Reviewed by: S. Shaefer Spires, MD, Duke University School of Medicine and Valeria Fabre, MD, Johns Hopkins University School of Medicine.

Three recent studies describe the effectiveness of mitigation strategies to protect healthcare workers (HCW) from occupational transmission of SARS-CoV-2 (COVID-19). First, Contejean and colleagues1 report on HCW positivity rates associated with a bundle of interventions including universal masking, hand hygiene emphasis, and use of recommended PPE (medical masking, gowns, gloves, eye protection, and N95 only for AGPs). They tested all symptomatic HCW for SARS-CoV-2 and found a 2.8% (373) positivity rate among all HCWs, with 3.2% in the adult hospital and 2.3% in the children’s hospital. As compliance with universal masking and COVID-19 PPE use improved, and close contact with unmasked employees reduced, the rate of HCW cases decreased.  Most positive HCW (70%) were in direct patient facing roles and 78% were outside dedicated COVID-19 units.  One major limitation of the study is the lack of a control group (negative HCWs) and that it only includes symptomatic HCWs to compare behaviors and exposures.

In a second study, Wang and colleagues2 reported findings of HCW SARS-CoV-2 positivity across a large health system in the northeast US before and after implementation of universal masking of all HCWs and patients. Of 9850 tested HCWs, 1271 (12.9%) were positive.  During the preintervention period, HCW positivity rate 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 health care system such as reduction in elective procedures, social distancing and increased masking in public.

In a third study, Seidelman and colleagues3 also investigated the impact of universal masking on HCW SARS-CoV-2 infection.  A unique aspect of this study was the attempt to classify SARS-CoV-2 positive employees as community-acquired, healthcare-acquired or unknown acquisition based on phone interviews with affected HCWs. Incidence rates of healthcare COVID-19 acquisition among HCW 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 HCWs did not work on COVID units. Of the healthcare-associated cases, 70% were related to unmasked exposure to another HCW and 30% were thought to be secondary to direct care of SARSCoV-2 positive patients. One week following the implementation of universal masking there was a significant decrease in the cumulative incidence rate of healthcare-acquired SARS-CoV-2 infections among HCWs.

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 co-worker or patient.  It is also notable that two of these studies noted a decrease in rate of HCW acquisition in the setting of increasing cases in their respective communities.


  1. Contejean A, Leporrier J, Canouï E, et al. Comparing dynamics and determinants of SARS-CoV-2 transmissions among health care workers of adult and pediatric settings in central Paris. Clin Infect Dis.
  2. Wang X, Ferro EG, Zhou G, Hashimoto D, Bhatt DL. Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers. JAMA. Published online July 14, 2020.
  3. Seidelman J, Lewis S, Advani S, et al. Universal Masking is an Effective Strategy to Flatten the SARS-CoV-2 Healthcare Worker Epidemiologic Curve. Infect Control Hosp Epidemiol. Published online June 25, 2020:1-5.
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