P-311. Shifts in Methicillin-Resistant <i>Staphylococcus aureus</i> Types in Bloodstream Infections: Nationwide and Regional Influences and Their Impact on Mortality

Abstract Background Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of bloodstream infections (BSI). In the USA and Japan, the New York/Japan clone (ST5-II) was historically prevalent, but recent studies in Japan have shown a shift towards ST8-IV and CC1-IV as the dominant strains. The extent to which these trends are mirrored in individual facilities and the variation in patient backgrounds across different MRSA types remains unclear. Methods We analyzed MRSA strains from blood cultures collected at Nagasaki University between 2012 and 2019. Whole-genome sequencing was utilized to determine sequence types, SCCmec, spa types, and resistance and virulence genes, complemented by phylogenetic analysis using core-genome MLST. Data were compared with earlier studies from 2003-2011 at the same hospital. Results Between 2003 and 2019, SCCmec type II decreased from 79.2% to 15.5%, whereas type IV increased from 18.2% to 65.5%. Severity and outcomes also changed: SOFA score decreased from 5.8 to 3.1, while in-hospital mortality decreased from 39.8% to 15.5%. No changes in the patient background, such as age, sex, or underlying diseases, were observed (Table 1). Further, the percentage of intravascular device-related BSI increased significantly from 18.1% during 2003–2007 to 46.6% during 2016–2019. The most common SCCmec type IV detected between 2012 and 2019 were ST8-IV and CC1-IV (Fig. 1A). ST8 was the predominant ST in both 2012–2015 and 2016–2019, but CC1 was detected only during 2016–2019 (Fig. 1B). In ST8-IV, MRSA/J and ST8-IV with spa type t5071 were identified, with MRSA/J being predominant. The detected MRSA/J, ST8-IV with spa type t5071, and CC1-IV subtypes were similar in terms of drug resistance, molecular characteristics, and phylogenetic features to those detected in the nationwide surveillance (Fig. 2). Patient characteristics across major MRSA types (ST8-IV, CC1-IV, ST8-I, ST5-II) revealed no significant differences, with lower SOFA scores and in-hospital mortality for CC1-IV (Table 2). Conclusion The evolving nature of MRSA types in bloodstream infections, correlating with improved outcomes over time and influenced by changes in nationally and regionally circulating strains, is highlighted. Disclosures Hiroshi Mukae, M.D., Ph.D., AstraZeneca: Lecture fees|Gilead Sciences: Lecture fees|GSK: Lecture fees|MSD: Advisor/Consultant|MSD: Lecture fees|Pfizer: Lecture fees|Shionogi &amp; Co., Ltd.: Advisor/Consultant|Shionogi &amp; Co., Ltd.: Grant/Research Support|Shionogi &amp; Co., Ltd.: Lecture fees