1740. Can Higher Minimum Inhibitory Concentration (MIC) to Vancomycin Predict Poor outcome in All Patients with Staphylococcus aureus Bacteremia?
Session: Poster Abstract Session: Treatment of Bacteremia and Endocarditis
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
  • IDSA_2013_poster_final.pdf (349.4 kB)
  • Background: A recent Australian study suggests that patients with Staphylococcus aureus bacteremia (SAB) with MIC >1.5 mcg/ml to Vancomycin (VAN) are at risk for higher all-cause 30 day mortality regardless of methicillin sensitivity. We conducted a study in the US to analyze the association of higher MIC to VAN with various clinical outcomes in both methicillin susceptible Staphylococcus aureus (MSSA) and methicillin resistant Staphylococcus aureus (MRSA) bacteremia.

    Methods: Case control study was conducted at 909-bed hospital. Cases (high MIC group) were all adult patients from 2009 to 2012 who had SAB with MIC > 1 mcg/ml to VAN. Controls (low MIC group) had SAB with MIC of ≤1 mcg/ml to VAN selected randomly from the same time period. Exclusion criteria were death within 72 hour of admission or transfer to another facility. Data collected included demographics, antibiotics used and various clinical outcomes. Fisher’s exact test and t test were used for analysis.

    Results: There were 71 patients (mean age 56, 60.5% male) in high MIC group (34 MRSA, 37 MSSA) and 79 patients (mean age 54, 54.5% male) in low MIC group (39 MRSA, 40 MSSA). All high MIC MRSA were treated with daptomycin, and 95% of low MIC MRSA with VAN. Majority of MSSA bacteremia were treated with β-lactam agents (100% in >1 / 87.5% in ≤1 MIC group). No statistically significant difference was found between the high MIC and low MIC SAB groups in regards to all-cause 30 day mortality (5.6% vs. 12.6%), complicated infections defined as presence of osteomyelitis, septic arthritis, endocarditis, epidural abscess, discitis or meningitis (25.5% vs.26.5%), ICU admissions (25.5% vs. 20.5%), mean length of stay (16 vs. 15 days), or prolonged bacteremia for > 48 hours (17.4 vs.10.2%). However, recurrences of SAB within 90 days were significantly higher in high MIC group (16.2% vs. 2.5%, p=0.019). All the recurrences were in MRSA group (32% in >1 vs. 5.1% in ≤ 1 MIC group, p=0.01). Neither the MIC >1 nor the MIC ≤ 1 MSSA group had any recurrence.

    Conclusion: Higher MIC to VAN appears to be associated with higher recurrence rate of MRSA bacteremia but was not associated with worse clinical outcome in MSSA bacteremia. Clinicians should not consider high MIC to VAN as a poor prognostic marker when treating patients for MSSA bacteremia.

    Wenyang Chen, BS, University of North Carolina Eshelman School of Pharmacy, Chapel Hill, NC, Michael Gooch, MS, RPh, Vidant Medical Center, Greenville, NC, Paul Cook, MD, Infectious Diseases, East Carolina University, Greenville, NC and Muhammad Salman Ashraf, MD, Infectious Disease, Brody School of Medicine, East Carolina University, Greenville, NC


    W. Chen, None

    M. Gooch, None

    P. Cook, Merck: Grant Investigator and Speaker's Bureau, Grant recipient and Speaker honorarium
    Pfizer: Grant Investigator, Grant recipient
    Gilead: Grant Investigator, Grant recipient
    Forest: Speaker's Bureau, Speaker honorarium

    M. S. Ashraf, None

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