Is reduced vancomycin susceptibility a factor associated with poor prognosis in MSSA bacteraemia?

Objectives: The known data about the influence of vancomycin MIC on Staphylococcus aureus bacteraemia are contradictory. Our objective was to study the possible impact of vancomycin MIC ≥1.5 mg/L on short- and medium-term mortality. Methods: A prospective cohort study was carried out from March 2008 to January 2011 on adult patients with MSSA bacteraemia admitted to a tertiary hospital located in Seville (Spain). We studied the relationship between vancomycin MIC, accessory gene regulator (agr) type and absence of d-haemolysin and poor prognosis. All isolates were genotyped by PFGE. Multivariate analysis, including a propensity score for having a vancomycin MIC of ≥1.5 mg/L, was performed by Cox regression. Results: One-hundred and thirty-five episodes of bacteraemia due to MSSAwere included in the analysis. Twentynine (21.5%) isolates had a vancomycin MIC of ≥1.5 mg/L by Etest. There were no differences in agr distribution or absence of d-haemolysin between isolates with reduced vancomycin susceptibility (RVS) and those without. RVS was not more frequent in specific clones; RVS was not associated with higher 14 or 30 day crude mortality SQ1 (RR¼0.44, 95% CI¼0.14 –1.35; and RR¼1.01, 95% CI¼0.52 –1.96) rates, and it did not show higher rates of complicated bacteraemia (14.2% versus 13.8%, P¼0.61). Cox regression analysis did not significantly modify the results for 14 day mortality (HR¼0.39, 95% CI¼0.11 –1.34) or 30 day mortality (HR¼0.89, 95% CI¼0.39 –2.04). Conclusions: Contrary to previously published data, we did not find a relationship between RVS and higher mortality in patients with MSSA bacteraemia and we did not find a link with higher complicated bacteraemia rates.