Study: Masking policies significantly reduce hospital-acquired viral respiratory infections

Editor's Note

A cohort study conducted across 10 hospitals in the Mass General Brigham system found that stopping universal masking and SARS-CoV-2 testing significantly increased hospital-onset respiratory viral infections, while reinstating masking for healthcare workers reduced those rates.

As detailed in a November 27 research letter in Jama Network Open, the study analyzed 641,483 hospital admissions from November 2020 to March 2024. The researchers used Poisson regression models to evaluate changes in infection rates across policy shifts, adjusting for seasonality. Hospital-onset infections were defined as those detected via PCR testing more than four days after admission.

Results were categorized into four periods: universal masking and testing pre-Omicron, universal masking and testing during Omicron, no universal masking or testing during Omicron, and masking for healthcare workers only during a winter surge in 2024. Key findings include:

• After stopping universal masking and testing, the proportion of hospital-onset infections relative to community-onset cases rose from 7.6% to 15.5%.
• Reinstating healthcare worker masking reduced the rate to 8.0%.
• Adjusted analysis revealed that ending masking and testing increased hospital-onset infection risk by 25% (rate ratio [RR], 1.25; 95% CI, 1.02-1.53), while resuming healthcare worker masking reduced the risk by 33% (RR, 0.67; 95% CI, 0.52-0.85).

Nosocomial respiratory viral infections are associated with longer hospital stays and higher mortality, researchers write. These results indicate that masking and testing can effectively reduce these infections, especially during periods of high community transmission. However, they caution that the study lacked concurrent control groups and could not fully account for effects of masking versus testing or variability in adherence to protocols.