387. Reduced Vancomycin Susceptibility and Staphylococcal Cassette Chromosome mec (SCCmec) Type Distribution in Methicillin-Resistant Staphylococcus aureus Bacteremia
Session: Poster Abstract Session: MRSA Molecular Epidemiology
Thursday, October 18, 2012
Room: SDCC Poster Hall F-H
Posters
  • SCCmecRVS.pdf (255.4 kB)
  • Background: Recent epidemiologic evidence indicates that community-associated and healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) strains are increasingly mixing in both community and healthcare settings. As such, it is possible that the genotypic and phenotypic characteristics that have typically distinguished community-associated MRSA and healthcare-associated MRSA strains may be evolving. The objective of this study was to examine the association between reduced vancomycin susceptibility (RVS) and staphylococcal cassette chromosome (SCCmec) type in MRSA bloodstream isolates.

    Methods: A cohort study of patients who were hospitalized from 2007 to 2009 with S. aureus bacteremia was conducted within a university health system. Bivariable analyses were conducted to determine the association between RVS and SCCmec type, as well as other microbiologic characteristics including Panton-Valentine leucocidin, accessory gene regulator (agr) dysfunction, and vancomycin hetero-resistance.

    Results: A total of 188 patients with MRSA bacteremia were identified during the study period: 116 (61.7%) and 72 (38.3%) patients had infections due to healthcare-associated MRSA and community-associated MRSA, respectively. As defined by a vancomycin Etest minimum inhibitory concentration (MIC) >1.0 mcg/mL, the prevalence of RVS was 40.4%. There was no significant change in the proportion of isolates with RVS over time during the study period (P=0.31, chi-square test for trend). Isolates with RVS were significantly more likely to be associated with SCCmec II compared to isolates without RVS (74.7% and 47.3%, respectively, P<0.001), but not Panton-Valentine leucocidin positivity (P=0.10), agr dysfunction (P=0.19), or healthcare-associated infection (P=0.36).

    Conclusion: The results of our study demonstrate important microbiologic characteristics among MRSA isolates characterized by RVS, including a significant association between SCCmec II and elevated vancomycin MIC. It is clear that the clinical and molecular epidemiology of MRSA is evolving, and further understanding of factors determining virulence will be important for elucidation of optimal treatment approaches for associated infections.

    Jennifer Han, MD1, Paul H. Edelstein, MD2, Ebbing Lautenbach, MD, MPH, MScE1,3,4 and the CDC Prevention Epicenter Program, (1)Division of Infectious Diseases, Dept. of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, (2)Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, (3)Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA, (4)Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, PA

    Disclosures:

    J. Han, None

    P. H. Edelstein, None

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

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