Air dispersal of meticillin-resistant Staphylococcus aureus in residential care homes for the elderly: implications for transmission during the COVID-19 pandemic

Abstract

Meticillin-resistant Staphylococcus aureus (MRSA) infections are rampant in hospitals and residential care homes for the elderly (RCHEs). To analyse the prevalence of MRSA colonization among residents and staff, and degree of environmental contamination and air dispersal of MRSA in RCHEs. Epidemiological and genetic analysis by whole-genome sequencing (WGS) in 12 RCHEs in Hong Kong. During the COVID-19 pandemic (from September to October 2021), 48.7% (380/781) of RCHE residents were found to harbour MRSA at any body site, and 8.5% (8/213) of staff were nasal MRSA carriers. Among 239 environmental samples, MRSA was found in 39.0% (16/41) of randomly selected resident rooms and 31.3% (62/198) of common areas. The common areas accessible by residents had significantly higher MRSA contamination rates than those that were not accessible by residents (37.2%, 46/121 vs. 22.1%, 17/177, P=0.028). Of 124 air samples, nine (7.3%) were MRSA-positive from four RCHEs. Air dispersal of MRSA was significantly associated with operating indoor fans in RCHEs (100%, 4/4 vs. 0%, 0/8, P=0.002). WGS of MRSA isolates collected from residents, staff and environmental and air samples showed that ST 1047 (CC1) lineage 1 constituted 43.1% (66/153) of all MRSA isolates. A distinctive predominant genetic lineage of MRSA in each RCHE was observed, suggestive of intra-RCHE transmission rather than clonal acquisition from the catchment hospital. MRSA control in RCHEs is no less important than in hospitals. Air dispersal of MRSA may be an important mechanism of dissemination in RCHEs with operating indoor fans.