1244. Prior Vancomycin Use Is a Risk Factor For Reduced Vancomycin Susceptibility In Methicillin-susceptible, But Not Methicillin-resistant, Staphylococcus aureus Bacteremia
Session: Poster Abstract Session: Staphylococcal Resistance and Epidemiology
Saturday, October 22, 2011
Room: Poster Hall B1
  • IDSA Poster.pdf (176.9 kB)
  • Background: Staphylococcus aureus is a significant cause of community- and healthcare-acquired infections and is associated with substantial morbidity and mortality.  Minimum inhibitory concentrations (MICs) for vancomycin among S. aureus have increased, and reduced vancomycin susceptibility (RVS) may be associated with vancomycin treatment failure.  We aimed to identify clinical risk factors for RVS in S. aureus (both methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA)) bacteremia.

    Methods: A case control study was performed at 2 centers from May 1, 2007 to December 31, 2009.  All adult patients with S. aureus bacteremia were included.  Cases were patients with a RVS S. aureus isolate (defined as vancomycin Etest MIC>1.0 ug/ml).  Controls were patients with a non-RVS S. aureus isolate.  Glycopeptide heteroresistance (hGISA) was screened by macro Etest method and confirmed by population analysis.   Daptomycin MICs were determined by microbroth dilution. 

    Results: Of 392 total subjects, 134 (34.2%) had RVS.  Fifty-eight of 202 (28.7%) patients with MSSA isolates had RVS and 76 of 190 (40.0%) patients with MRSA isolates had RVS.  In unadjusted analyses, prior vancomycin use was associated with RVS (OR, 2.08 [95% CI, 1.00-4.32]; P=0.046).  In stratified analysis, there was significant effect modification by methicillin susceptibility on the association between vancomycin use and RVS (P=0.04). In multivariable analysis, after controlling for hospital of admission and prior levofloxacin use, the association between vancomycin use and RVS was significant for patients with MSSA [adjusted OR, 4.02 (95% CI, 1.11-14.50)] but not MRSA infection [adjusted OR, 0.87 (95% CI, 0.36-2.13)].  Seventeen (12.7%) RVS isolates exhibited hGISA compared to 3 (1.2%) non-RVS isolates (P<0.001).  The geometric mean daptomycin MIC for RVS isolates was 0.13 ug/ml compared to 0.08 ug/ml for non-RVS isolates (P<0.001).     

    Conclusion: A substantial proportion of patients with S. aureus bacteremia had RVS.  The association between prior vancomycin use and RVS was statistically significant for patients with MSSA but not MRSA infection.  This suggests a complex relationship between the clinical and molecular epidemiology of RVS in S. aureus.


    Subject Category: A. Antimicrobial agents and Resistance

    Kara B. Mascitti, MD1, Paul H. Edelstein, MD2, Neil Fishman, MD3, Knashawn H. Morales, ScD4,5, Andrew J. Baltus2 and Ebbing Lautenbach, MD MPH MSCE4, (1)Division of Infectious Diseases, Department of Medicine, St. Luke's Hospital and Health Network, Bethlehem, PA, (2)Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, (3)Division of Infectious Diseases, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, (4)Department of Biostatistics and Epidemiology, Center for Clinical Epidemiology and Biostatistics , University of Pennsylvania School of Medicine, Philadelphia, PA, (5)Hospital of the University of Pennsylvania, Philadelphia, PA


    K. B. Mascitti, None

    P. H. Edelstein, None

    N. Fishman, None

    K. H. Morales, None

    A. J. Baltus, None

    E. Lautenbach, Cubist Pharmaceuticals: Grant Investigator, Research grant
    Merck: Grant Investigator, Research grant
    AstraZeneca: Grant Investigator, Research grant
    3M: Grant Investigator, Research grant

    Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.