Herd protection effect of N95 respirators in healthcare workers

Objective To determine if there was herd protection conferred to unprotected healthcare workers (HCWs) by N95 respirators worn by colleagues.Methods Data were analysed from a prospective cluster randomized clinical trial conducted in Beijing, China between 1 December 2008 and 15 January 2009. A minimum compliance level (MCL) of N95 respirators for prevention of clinical respiratory illness (CRI) was set based on various compliance cut-offs. The CRI rates were compared between compliant (≥MCL) and non-compliant (<MCL) N95 wearers by ward, and between non-compliant wearers and control subjects who did not wear masks.Results Data were analysed from 949 HCWs who wore N95 respirators and 125 HCWs who did not wear masks. At 50% MCL there were no significant differences in the CRI rates between compliant and non-compliant N95 wearers by ward. In multivariate analysis, the CRI rate in non-compliant HCWs was significantly lower compared with controls (relative risk 0.26; 95% confidence interval 0.08, 0.82).Conclusion This study suggests herd protection from use of N95 respirators by colleagues within a hospital ward.