Evolution of Community-Associated MRSA in Region Örebro County, Sweden

Methicillin resistant Staphylococcus aureus have been an issue in healthcare since the 1960s. Initially residing in healthcare establishments but in the late 1990s emerging without healthcare connection. The mechanisms of intercontinental and national spread are not fully understood, as sometimes novel outbreaks occur without any identifiable source or connection to locally dominant clonal clusters. This study investigates the epidemiology and genomics of CA-MRSA in Region Örebro County, Sweden, through 330 isolates collected between 2000 and 2019. A shift in the dominant sequence type from ST80 to ST22, and an increase in prevalence of STs belonging to CC5 and CC22 had occurred in 2011-2019. Both ST8 and ST80 isolates seem to give way to emerging ST22 isolates also indicated by the declining presence of the USA300 clone. The Staphylococcal chromosomal cassette mec type IV remained dominant, indicating that the SCCmec type IV is relatively geographically stable. This is possibly due to its low cost of fitness and transductal capabilities, which warrants further studies of SCCmec type IV survival mechanics as well as migratory flows effects on local epidemiology in preparation of future possible outbreaks.