Objective MRSA strains that are less susceptible to vancomycin have increased recently but studies on the clinical course and prognosis of the bacteremia that differ in vancomycin MIC have been rarely done. The purpose of this study is to compare the clinical characteristics and outcomes of MRSA bacteremia with different vancomycin MICs.
Methods Eighty-two adult patients with MRSA bacteremia and their first blood isolates from November, 2003 to May, 2005 at a tertiary-care teaching hospital in Seoul, were studied. The MICs of vancomycin were measured by agar dilution method. Patients were assigned into two groups; patients with MIC equal or more than 2 µg/ml were classified as the case group and those with MIC equal or less than 1 µg/ml as the control group.
Results Twenty-eight patients were classified as case group and 54 were classified as control group. There were no significant differences in age/sex, underlying disease, duration of hospital stay, prior antibiotic use, and portal of entry between the case and control groups. However, the admission history in the recent 3 months were more common (82.1%[23/28] vs. 59.3%[32/54], P = 0.037) in the case group and infective endocarditis was developed more frequently in the case group (10.7%[3/28] vs. 0%[0/54], P = 0.014). There were no statistically significant difference in the overall mortality (42.9% vs. 64.6%, P = 0.125) and bacteremia-related mortality (23.1% vs. 18.8%, P = 0.658).
Conclusions MRSA bacteremia with vancomycin MIC ≥ 2 µg/ml was more commonly associated with recent admission history and infective endocarditis than that with vancomycin MIC ≤ 1 µg/ml. However, there were no significant differences in mortality rates between two groups.