Clinical, microbiologic, and genetic determinants of persistent methicillin-resistant Staphylococcus aureus bacteremia

Abstract

Methicillin-resistant Staphylococcus aureus bacteremia (MRSAB) often persists despite full susceptibility to vancomycin; therefore, associated factors were assessed. A retrospective cohort analysis of 222 patients with MRSAB treated with vancomycin was conducted; patients with persistent MRSAB (pMRSAB) were compared to those with nonpersistent bacteremia (NPB). Incidence of pMRSAB was 9%. More patients with vancomycin MIC = 2 mg/L had pMRSAB (16%) compared to patients with vancomycin MIC <2 mg/L (5%), P = 0.012. SCC mec type and Panton–Valentine leukocidin production were similar between patients with pMRSAB and NPB. There was no difference in vancomycin troughs, time to first dose, or area under the concentration–time curve/MIC between groups. More metastatic complications were observed in pMRSAB 63% versus NPB 32% ( P = 0.005). Multivariate analysis found endocarditis (odds ratio [OR], 2.3; P = 0.021), complicated MRSAB (OR, 2.6; P = 0.009), vancomycin MIC = 2 (OR, 2.6; P = 0.009), and septic shock (OR 2.2 P = 0.031), which were independent predictors of pMRSAB.