Impact of molecular epidemiology and reduced susceptibility to glycopeptides and daptomycin on outcomes of patients with methicillin-resistant Staphylococcus aureus bacteremia

Background Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia was associated with high mortality, but the risk factors associated with mortality remain controversial. Methods A retrospective cohort study was designed. All patients with MRSA bacteremia admitted were screened and collected for their clinical presentations and laboratory characteristics. Minimum inhibitory concentration (MIC) and staphylococcal cassette chromosome mec (SCCmec) type of bacterial isolates were determined. Risk factors for mortality were analyzed. Results Most MRSA isolates from the 189 enrolled patients showed reduced susceptibility to antibiotics, including MIC of vancomycin ≥1.5 mg/L (79.9%), teicoplanin≥2 mg/L (86.2%), daptomycin≥0.38 mg/L (73.0%) and linezolid≥1.5 mg/L (64.0%). MRSA with vancomycin MIC≥1.5 mg/L and inappropriate initial therapy were the two most important risk factors for mortality (both P < 0.05; odds ratio=7.88 and 6.78). Hospital-associated MRSA (HAMRSA), carrying SCCmec type I, II, or III, was associated with reduced susceptibility to vancomycin, teicoplanin or daptomycin and also with higher attributable mortality (all P < 0.05). Creeping vancomycin MIC was linked to higher MIC of teicoplanin and daptomycin (both P < 0.001), but not linezolid (P=0.759). Conclusions Giving empirical broad-spectrum antibiotics for at least 5 days to treat catheter-related infections, pneumonia, soft tissue infection and other infections was the most important risk factor for acquiring subsequent HA-MRSA infection. Choice of effective anti-MRSA agents for treating MRSA bacteremia should be based on MIC of vancomycin, teicoplanin and daptomycin. Initiation of an effective anti-MRSA agent without elevated MIC in 2 days is crucial for reducing mortality.