The relationship between vancomycin tolerance and clinical outcomes in patients with Staphylococcus aureus bacteremia

Abstract

Background: Treatment failure is increasingly common in Staphylococcus aureus bacteremia (SAB). Vancomycin tolerance may be playing a role in clinical outcomes in SAB that has yet to be fully explored. Methods: This was a single-center retrospective cohort study of 166 patients (September 2012 - January 2014) evaluating the relationship between vancomycin tolerance and clinical failure in SAB. Vancomycin minimum inhibitory concentration (MIC) was determined by broth microdilution and Etest. Vancomycin tolerance was defined as a vancomycin minimum bactericidal concentration (MBC)/MIC greater than or equal to 32. Univariable and multivariable analyses were conducted to determine the relationship between vancomycin tolerance and clinical failure after adjusting for other factors. Results: Of the 166 patients evaluated, 26.5% had vancomycin tolerant clinical isolates. Tolerance to vancomycin was more common in methicillin-susceptible S. aureus bacteremia (MSSA-B) than methicillin-resistant S. aureus bacteremia (MRSA-B; n=29/101 [28.7%] vs. n=15/65 [23.1%]), although not significantly (P=0.422). Clinical failure was frequently observed (50% overall). Elevated vancomycin MIC by Etest (greater than or equal to 1.5 mcg/mL) was not associated with clinical failure (P=0.50). Vancomycin tolerance was significantly associated with SAB clinical failure in univariable analysis (P=0.014). This relationship persisted even when adjusting for other factors in multivariable analysis (adjusted odds ratio [AOR], 2.70; 95% confidence interval [CI], 1.27-5.70; P=0.010). Conclusions: Vancomycin tolerance is a clinically significant predictor of clinical failure in SAB independent of methicillin susceptibility and antibiotic choice. Future research is needed to determine optimal treatment of vancomycin tolerant SAB.