Effect of a national policy of universal masking and uniform criteria for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) exposure on hospital staff infection and quarantine.

Objective: To determine the effect of 2 regulations issued by the Israel Ministry of Health on coronavirus disease 2019 (COVID-19) infections and quarantine among healthcare workers (HCWs) in general hospitals.

Design: Before-and-after intervention study without a control group (interrupted time-series analysis).

Setting: All 29 Israeli general hospitals.

Participants: All HCWs.

Interventions: Two national regulations were issued on March 25, 2020: one required universal masking of HCWs, patients, and visitors in general hospitals and the second defined what constitutes HCW exposure to severe acute respiratory coronavirus virus 2 (SARS-CoV-2) and when quarantine is required.

Results: Overall, 283 HCWs were infected at work or from an unknown source. Before the intervention, the number of HCWs infected at work increased by 0.5 per day (95% confidence interval [CI], 0.2-0.7; < .001), peaking at 16. After the intervention, new infections declined by 0.2 per day (95% CI, -0.3 to -0.1; < .001). Before the intervention, the number of HCWs in quarantine or isolation increased by 97 per day (95% CI, 90-104; < .001), peaking at 2,444. After the intervention, prevalence decreased by 59 per day (95% CI, -72 to -46; < .001). Epidemiological investigations determined that the most common source of HCW infection (58%) was a coworker.

Conclusions: Universal masking in general hospitals reduced the risk of hospital-acquired COVID-19 among HCWs. Universal masking combined with uniform definitions of HCW exposure and criteria for quarantine limited the absence of HCWs from the workforce.