Did universal masking during the COVID-19 pandemic reduce MRSA and MSSA acquisition in the NICU?

Objectives: To assess whether universal masking during the COVID-19 pandemic reduced neonatal acquisition of S. aureus.

Study design: We performed a retrospective cohort study of neonates admitted to a level three regional NICU for three years before and after implementation of universal masking for the COVID-19 pandemic. Multivariable proportional hazards regression models evaluated the effect of masking on time-to-acquisition of methicillin-resistant and methicillin-sensitive S. aureus (MRSA and MSSA) while adjusting for fixed and time-varying neonatal characteristics.

Results: We analyzed 2,728 neonates, 1,446 pre-pandemic and 1,282 post-pandemic; 84.9% were inborn, with mean gestational age of 34 weeks and 6 days (SD = 4.2) and mean birthweight of 2,500 grams (SD = 975). The mean number of screening cultures per neonate was 3.07 (SD = 3.31). When adjusting for covariates, universal masking was associated with decreased acquisition of MRSA (hazard ratio =0.43 (95% CI: 0.19-0.99), p = 0.04) but not MSSA (HR = 1.27 (95% CI: 00.87-1.85), p = 0.21). Among covariates, airway devices and maternal S. aureus status were associated with S. aureus acquisition.

Conclusions: Universal masking decreased the rate of NICU MRSA acquisition by 60% while MSSA acquisition was unchanged. Masking may reduce MRSA spread via colonized healthcare personnel while MSSA may be more likely to be acquired from parental skin-to-skin contact and was thus unaffected by masking.