1257. Methicillin-resistant Staphylococcus aureus (MRSA) Bacteremia: Correlation between Vancomycin Minimum Inhibitory Concentration Values by the Broth Microdilution Method and Treatment Outcome
Session: Poster Abstract Session: Staphylococcal Resistance and Epidemiology
Saturday, October 22, 2011
Room: Poster Hall B1
  • IDSA No.1257.pdf (652.4 kB)
  • Background: There has been little research evaluating the correlation between vancomycin (VAN) minimum inhibitory concentration (MIC) and treatment outcome in MRSA bacteremia using the reference broth microdilution (BMD) for VAN susceptibility determination. Most previous studies used E test for VAN MIC determination, but E test has been shown to provide VAN MIC results consistently higher than those provided by precisely performed reference BMD tests.

    Methods: Using a reference BMD method, we determined the VAN MICs for MRSA isolated from 51 patients (pts) with MRSA bacteremia between Dec.2007 and Dec.2010 at St. Luke’s International Hospital , 530 bed ,acute care teaching hospital in Tokyo. We retrospectively reviewed medical records and compared the clinical background and 30-day mortality after the first positive blood cultures between MRSA infected pts with low VAN MIC (MIC=0.5 or 1.0μg/ml) versus high MIC (MIC=2.0μg/ml).

    Results: Among 51 MRSA isolates, 23.5% (12 /51) had a MIC=0.5μg/ml, 60.8% (31 /51) had a MIC=1.0μg/ml ,and 15.7% (8 /51) had a MIC=2.0μg/ml. Between the 43 pts with low MIC and the 8 pts with high MIC, there were no significant differences in age, baseline diseases, focus of infections or prior use of VAN. Eight pts with terminal stage malignancy or under palliative care were excluded from the evaluation of mortality. All of the remaining 43 pts (6 in high MIC and 37 in low MIC group) were initially treated with VAN. VAN was changed to linezolid in 16.6% (1 /6) high MIC pts and 10.8%(4 /37) low MIC pts due to adverse reactions to VAN in 4 pts and clinically resistant vascular graft infection in 1 low MIC pt. Combination therapy(5 pts VAN+RFP+TMP/SMX, 4 pts VAN+RFP) was given in 9 pts (23.2%) in low MIC group only. The 30-day mortality associated with MRSA bacteremia was as follows: 23.3% (10 /43) in total, 27% (10 /37) in low MIC group ,and 0% (0 /6) in high MIC group (P=0.31, Fisher’s exact test)

    Conclusion: In 30-day mortality associated with MRSA bacteremia, there was no significant difference between pts with high MIC (MIC=2.0μg/ml) and pts with low MIC (MIC=0.5 or 1.0μg/ml) determined by the CLSI reference BMD method.

    Subject Category: C. Clinical studies of bacterial infections and antibacterials including sexually transmitted diseases and mycobacterial infections (surveys, epidemiology, and clinical trials)

    Keiichi Furukawa, MD, Infectious Diseases, St Luke's International Hospital, Tokyo, Japan, Yumiko Mikami, Department of Laboratory Medicine, St Luke' International Hospital, Tokyo, Japan and Kyoko Yokota, MD, Division of Infectious Diseases, St Luke's International Hospital, Tokyo, Japan


    K. Furukawa, None

    Y. Mikami, None

    K. Yokota, None

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