SARS-CoV-2 Positivity and Mask Utilization Among Health Care Workers

This cohort study examines the association of mask use with COVID-19 transmission among health care workers in California.


Introduction
Human-to-human transmission of SARS-CoV-2 occurs during exposure to infectious respiratory droplets or aerosols generated by humans with COVID-19. 1 Aerosolizing events (AEs) contribute to the controversy regarding the selection of optimal personal protective equipment (PPE) for preventing transmission of SARS-CoV-2 to health care workers (HCWs). Because of global PPE shortages, 2 further studies examining the association of HCW PPE use with the acquisition of COVID-19 are needed to protect our HCWs and decrease inappropriate PPE use.

Methods
We conducted a retrospective cohort study in a single service area at Kaiser Permanente Southern California (KPSC), identifying all HCWs who underwent testing for COVID-19 by polymerase chain reaction during March 13 through August 3, 2020. HCWs were identified for testing either through (1) exposure to a patient with COVID-19 or (2) symptomatology of potential COVID-19 as defined by US Centers for Disease and Control and Prevention (CDC) criteria. 3 The exposure definition at our institution aligned with CDC criteria. 4 The KPSC institutional review board approved this study and waived informed consent because data were deidentified and involved no more than minimal risk to participants. We followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cohort studies.
Contact tracing by structured interview was conducted with all HCWs who underwent testing.
This process consisted of documentation of exposure status, masking protocol compliance, and testing results. The testing protocol for exposed HCWs was initiated on the day when exposure was identified, then again 5 to 7 days after exposure, and finally at day 14 after exposure. A symptomatic HCW was tested on the first day of reported symptoms. Logistic regression was used to assess the association between mask usage and test positivity. Analysis was performed using SAS software version 9.4 (SAS Institute) with 2-tailed testing and P < .05 as the statistical significance level.

Discussion
Our study found no association in positivity rates among HCW wearing RM vs MM when performing nonaerosolizing, routine patient care, supporting findings from a recent case-control study 5 and an earlier case report 6 suggesting that MM protected HCWs from acquiring COVID-19. Only 4 positive tests followed exposure events (2 among nursing staff, 2 among technician staff), none were from confirmed AEs, and all occurred prior to universal masking implementation. More than 95% of HCWs acquired COVID-19 outside of a known patient-related exposure event, possibly due to improper donning and doffing of masks during social interactions with other HCWs in the workplace or in the community, supporting a study 5 finding higher risk of COVID-19 transmission outside of patient care interactions.
Our low exposure conversion may reflect the low incidence of AEs in our data set and early adoption of universal masking. These factors may have decreased high-risk exposures of unmasked HCWs to unmasked infectious patients.
Strengths of our study include delineating a large cohort with complete individual-level masking and testing data to quantify risk of COVID-19 in the health care setting. Limitations of our study include the potential for recall bias during contact tracing interviews, the unavailability of whole genome sequencing at our institution to confirm the transmission event, and the retrospective nature of the study design. Randomized studies in mask optimization would be ideal, although they may face challenges in enrollment.

JAMA Network Open | Infectious Diseases
SARS-CoV-2 Positivity and Mask Utilization Among Health Care Workers