Dynamic Networks of Methicillin-Resistant Staphylococcus aureus in Communities Drive Hospital Transmission

Although methicillin-resistant Staphylococcus aureus (MRSA) transmission has traditionally been viewed separately in hospital and community settings, this distinction is increasingly blurred. We used whole-genome sequencing and epidemiologic analyses to characterize the movement of MRSA across these interfaces in a rural-urban population.

Serial cross-sectional sampling of MRSA isolates occurred at a tertiary care hospital between 2010 and 2019. Community-onset MRSA was prospectively isolated from patients presenting to the emergency department with acute skin and soft tissue infections (SSTIs), while hospital-onset MRSA was sampled before (2010), during (2015-2017), and after (2019) this community collection period. MRSA transmission was assessed using a joint application of epidemiological approaches and phylodynamic analysis of whole-genome sequences.

After whole-genome sequencing on community and hospital MRSA isolates, phylogenetic analysis revealed 2 major clades distinguished by clonal complex (CC) CC8/t008 and CC5/t002 spa types. Multiple independent introductions of MRSA lineages from the community to the hospital were observed. Geographic clustering of community-onset MRSA was uniquely present outside of the urban center. Subjects with rural residence or livestock exposure were more likely to have community-onset MRSA SSTI compared with those with non-MRSA SSTI.

MRSA transmission in hospital settings was introduced from strains with ancestral origins in community settings. Although community-onset MRSA transmission appears sustained with limited influence from hospital strains, more comprehensive surveillance is required to quantify this relationship. Nosocomial MRSA outbreak prevention strategies should target unique aspects of the community in addition to the hospital, particularly hot spots, risk behaviors, and strain reservoirs.