721Decreasing Prevalence of Vancomycin-Heteroresistance (hVISA) among Methicillin-Resistant Staphylococcus aureus (MRSA) Blood Isolates over 10 years: Potential Impact of Vancomycin Treatment Guidelines

Methods. Standardized screening of MRSA blood isolates saved from 2002-2012 for hVISA and VISA on BHI agar supplemented with vancomycin 3 and 4 mg/L, respectively (previously shown to be the best screening method based on correlation with population analysis profile). One isolate was selected from each patient and trends were analyzed over time. Results. We encountered 1231 patients with SAB, MRSA accounted for 729 (59.2%). Screening for hVISA was possible for 728 isolates (one isolate could not be recovered for testing). Vancomycin MIC (Etest) was stable between 2002 and 2009 but decreased in 2010-12 (table). The incidence of isolates with vancomycin MIC ≥2mg/L and heteroresistance steadily decreased whereas the changes in VISA prevalence was not significant. Conclusion. Standardized screening using BHI agar supplemented with vancomycin revealed a steadily decreasing incidence of hVISA and isolates with vancomycin MIC ≥2mg/L. The reasons for these trends are uncertain but adherence to updated vancomycin treatment guidelines which advocate for high vancomycin trough levels may suppress the development of less susceptible progeny. VISA remains rare. Disclosures. All authors: No reported disclosures.