Program Schedule

The Relationship between Vancomycin Minimum Inhibitory Concentrations (MICs) and Treatment Failure among Patients with Methicillin-Resistant Staphylococcus aureus Blood Stream Infections (MRSA-BSI) at the University of Connecticut Health Center (UCHC)

Session: Poster Abstract Session: Treatment of Antimicrobial Resistant Infections
Thursday, October 9, 2014
Room: The Pennsylvania Convention Center: IDExpo Hall BC
  • Gemtessa IDWeek 2014 Poster.pdf (1.1 MB)
  • Background:

    MRSA-BSI has been associated with mortality rates of 20-30%. In recent publications, many factors have been associated with increased risks of treatment failure, including vancomycin MIC >1 μg/ml. Over the past few years, we have observed a substantial increase in the prevalence of MRSA with vancomycin MICs of 2 μg/ml. The purpose of our study is to compare the treatment outcomes of patients with MRSA-BSIs caused by MRSA strains with vancomycin MICs of 1 μg/mL versus 2 μg/mL.


    This is an ongoing retrospective observational cohort study of adult patients with MRSA-BSIs that occurred between January 2008-November 2013. Patients were included in the cohort if they were treated with vancomycin for >3 days and had at least 1 serum vancomycin level obtained during therapy. The primary outcome is treatment failure defined as: a composite of 30-day mortality; persistent bacteremia for ≥ 5 days; or clinical nonresponse. Previous published studies using this composite endpoint have reported treatment failure rates of 39% to 53%. Therefore, we used an anticipated difference in treatment failure rate of 25%. An adequate sample size (based on α error of 0.05 and β error of 80%) would be 102 patients in order to achieve adequate power.


    Thus far data have been collected and evaluated for a total of 33 patients; vancomycin MICs were 1 μg/mL and 2 μg/mL for 16 and 17 patients, respectively. The median ages were 59 (range 23-92) and 57 years (range 21-85) respectively. There were 11 male and 5 female patients in the MIC ≤1 μg/ml group compared to 8 male and 9 female patients in the MIC ≥2 μg/ml group. Treatment failure was higher in the MIC ≥2 μg/ml group (10/17=64.7%) compared to the MIC ≤1 μg/ml group (6/16=37.5%). Treatment failure was predominantly related to higher numbers of patients with persistent bacteremia in the MIC ≥2 μg/ml group (7/17=41.2%) compared to the MIC ≤1 μg/ml group (3/16=18.8%). There were 6 patients in the MIC ≥2 μg/ml group who required ICU level of care as compared to 3 patients in the MIC ≤1 μg/ml group.


    A preliminary analysis of data from 33 patients has already revealed a numerical trend towards higher prevalence of treatment failure driven by persistent bacteremia for the patients who had MRSA-BSIs caused by strains with vancomycin MIC ≥2 μg/ml.

    Tilahun Amdissa Gemtessa, MD, Division of Infectious Diseases, University of Connecticut Health Center, Farmington, CT, Trini Ann Mathew, MD, MPH, FACP, Division of Infectious Diseases, Department of Medicine, University of Connecticut, Farmington, CT and Jeffrey R. Aeschlimann, Pharm.D., Dept. of Pharmacy Practice, Univ. of Connecticut School of Pharmacy, Farmington, CT


    T. A. Gemtessa, None

    T. A. Mathew, None

    J. R. Aeschlimann, None

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