Strain Differences in Bloodstream and Skin Infection MRSA isolated between 2019-2021 in a Single Health System

S. aureus is a common cause of skin and soft tissue infections (SSTIs) and has recently become the most common cause of bloodstream infections (BSIs), but whether the strains causing these two clinical syndromes overlap has not been studied adequately. USA300/500 (clonal complex [CC] 8-ST8) and USA100 (CC5-ST5) have dominated among methicillin-resistant S. aureus (MRSA) strains in the U.S. since the early 2000s. We compared the genomes of unselected MRSA isolates from 131 SSTIs with those from 145 BSIs at a single U.S. center in overlapping periods in 2018-2021. CC8 MRSA was more common among SSTIs and CC5 was more common among BSIs, consistent with prior literature. Based on clustering genomes with a threshold of 15 single nucleotide polymorphisms (SNPs), we identified clusters limited to SSTI patients and separate clusters exclusively comprising BSI patients. However, we additionally identified 8 outbreak clusters that included at least one SSTI and one BSI isolate. This suggests that virulent MRSA strains are transmitted from person-to-person locally in the healthcare setting and the community and that single lineages are often capable of causing both SSTIs and BSIs.