ST8 and ST72 Methicillin-Resistant S. aureus Bacteremia in Korea: A Comparative Analysis of Clinical and Microbiological Characteristics

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) remains a major cause of bloodstream infection worldwide. In Korea, sequence type (ST) 72 has predominated, whereas ST8, including the USA300 lineage, has recently emerged. Comparative data on these genotypes in MRSA bacteremia (MRSAB) are limited. We conducted a retrospective cohort study of adult patients with MRSAB admitted to a 2700-bed tertiary care hospital in Republic of Korea between July 2008 and December 2020. Clinical features and outcomes of patients with ST8 MRSA were compared with those of patients with ST72 MRSA. Among 1975 cases of <i>S. aureus</i> bacteremia, 998 (50.5%) were due to MRSA, including 327 (32.7%) ST72 and 23 (2.3%) ST8 isolates. Demographics and comorbidities were similar, though pneumonia appeared more frequent in ST8 cases without statistical significance. ST8 isolates exhibited greater resistance to ciprofloxacin and erythromycin and more frequent vancomycin E-test MICs ≥1 mg/L, while broth microdilution MICs were comparable. <i>spa</i> type distribution differed, with t324 predominating in ST72 and t008 in ST8. Management practices, persistent bacteremia, recurrence, and 30- and 90-day mortality did not differ significantly. In multivariable analysis, liver cirrhosis and Charlson comorbidity index >4, but not MRSA genotype, independently predicted 30-day mortality. These findings highlight the importance of continued surveillance of emerging ST8 clones.