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

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. SCCmec 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.