Trends in health care-associated non-SARS-CoV-2 respiratory viral infections in conjunction with masking policies during and after the COVID-19 pandemic: A time-series analysis.

Background: While introduction of universal masking was associated with significant declines in health care-associated-respiratory-viral-infections (HA-RVI), subsequent studies have shown mixed results. We sought to evaluate the impact on HA-RVI when masking was continued in the postpandemic period.

Methods: Observational study in 2 Singaporean hospitals from January 1, 2016 to April 30, 2024. Prepandemic, masking (surgical masks) was only practiced in high-risk wards. During the pandemic, masking was made mandatory hospital-wide, together with other extensive mitigation measures; in the postpandemic phase, other mitigation measures were stood-down but masking in hospitals was continued. Interrupted time-series analysis was utilized to compare trends in HA-RVI.

Results: During the pandemic, HA-RVI fell to near-zero. In the postpandemic phase, when other mitigation measures were stood-down but masking in hospitals was continued, HA-RVI rebounded. Time-series analysis showed immediate decrease in HA-RVI following imposition of universal masking, together with other mitigation measures during the pandemic; postpandemic, there was both an immediate increase in HA-RVI, as well as a significant increase in the trend of HA-RVI over time, despite continuation of masking.

Conclusions: HA-RVI rebounded in the postpandemic period after other mitigation measures were stood-down, even whilst masking continued in hospitals.