Predictors of persistent methicillin-resistant Staphylococcus aureus bacteraemia in patients treated with vancomycin

Objectives: The high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) coupled with an increase in vancomycin use have induced vancomycin tolerance in MRSA, adversely affecting the outcome of MRSA bacteraemia. This study aimed to identify predictors of persistent MRSA bacteraemia (PMRSAB) in patients treated with vancomycin. Methods: A retrospective, case-control study was performed at a university hospital in Korea from January 2006 to February 2009. Subjects included 96 patients who had MRSA bacteraemia and received vancomycin under therapeutic drug monitoring. We compared the clinical characteristics, management and outcomes of cases with PMRSAB (≥7 days, n=31) with controls with non-PMRSAB (≤3 days, n=32). Vancomycin MICs were determined by the Vitek 2 system. Results: Of 96 patients with MRSA bacteraemia, MRSA isolates from 21 patients (21.9%) showed a vancomycin MIC of 2 mg/L. Independent predictors of PMRSAB were: retention of implicated medical devices [odds ratio (OR), 10.35; 95% confidence interval (CI), 1.03-104.55]; MRSA infection of at least two sites (OR, 10.24; 95% CI, 1.72-61.01); and vancomycin MIC of 2 mg/L (OR, 6.34; 95% CI, 1.21-33.09). The frequency of side effects and mean trough serum vancomycin concentrations were not significantly different between the two groups. Sixteen patients with PMRSAB subsequently received teicoplanin±arbekacin, linezolid or quinupristin/dalfopristin, due to vancomycin failure or intolerance. Conclusions: To minimize the risk of PMRSAB, early removal of implicated devices and evaluation for metastatic infections should be encouraged. Alternative antibiotic therapy is warranted for infections due to isolates with elevated vancomycin MICs, as well as for the high rates of side effects.