K-564. MRSA Bacteremia: Effects of Vancomycin MICs on Outcome
Session: Poster Session: Staphylococcus aureus: Vancomycin Use, Resistance, and Treatment Failure
Saturday, October 25, 2008: 12:00 AM
Room: Hall C
Background: Treatment failures for vancomycin (vanco) in Methicillin Resistant Staphylococcus Aureus (MRSA) infections have been reported for vanco Minimal Inhibitory Concentration (MIC) > 2ug/ml. In 2006, the vanco susceptibility breakpoint was lowered from 4ug/ml to 2ug/ml. The aim of our study was to evaluate the MIC trend for vanco in MRSA blood cultures and to determine the effect of MIC on outcome in MRSA bacteremia. Methods: This was an observational retrospective study of patients hospitalized at Albert Einstein Medical Center with MRSA bacteremia from January 2002 to June 2007. 161 patients were eligible for the study. Patients ≤18 years, or received vanco ≤72 hrs were excluded. Patients were divided into a high MIC group (MIC=2) or a low MIC group (MIC<2). Primary outcome measures included 30 day mortality, infection related complications and persistent bacteremia for > 7 days. Bivariate comparison between the two MIC groups and outcome of interest was calculated using Chi Square. Results: There was a significant increase in the number of MRSA blood culture isolates with an MIC 2 µg/ml from 2002-2004, 14/64 (22%), vs 37/97 (38.1%) of isolates from 2005-June 2007 (p=0.03). Demographics, comorbidities, severity of illness and prior vanco usage were similar between the low and high MIC groups. Outcome measures were as follows:
OutcomeLow MIC(< 2 µg/ml)High MIC(= 2 µg/ml)P value
30-day mortality20/107 (18.7%)10/54 (18.5%)0.90
Infection related complications17/104 (16.3%)11/54 (20.4%)0.50
Persistent bacteremia >7 days9/104 (8.65%)11/54 (20.4%)0.03
Conclusions: MRSA blood culture isolates with a vanco MIC = 2 have increased in our institution since 2002. A vanco MIC =2 was associated with persistent bacteremia but not with an increase in mortality or infection related complications and suggest increased vanco tolerance but decreased virulence in these MRSA isolates. Alternative treatment strategies need to be investigated for MRSA bacteremias with a vanco MIC=2.
Ikjot Kaur, MD1, Jerry Zuckerman, MD1, Sherry Pomerantz, PhD1 and  I. Kaur, None., (1)Albert Einstein Medical Center, Philadelphia, PA