844. Elevated vancomycin MIC and presence of deep seated infection in Staphylococcus aureus bacteremia
Session: Poster Abstract Session: Bacteremia and Endocarditis
Friday, October 9, 2015
Room: Poster Hall
Background: Staphylococcus aureus bacteremia (SAB) is a common bloodstream infection that results in significant mortality and morbidity.  The effect of the infecting isolate’s vancomycin minimum inhibitory concentration (MIC) on treatment failure is not clear.  We hypothesize that an elevated vancomycin MIC is only predictive of failure when treating a deep seated S. aureus infection. 

Methods: All patients from 5 Intermountain Healthcare hospitals with ≥ 1 blood culture positive for S.aureus were included.  Data were obtained through manual chart review as well as Enterprise Data Warehouse (EDW) extraction.  MIC was evaluated by routine automated methods (Phoenix) as well as E-test performed on stored bacterial isolates per standard protocol. Failure was defined as: all cause 60-day mortality, growth of S. aureus in blood cultures ≥7 days after index culture while on therapy, or recurrence of bacteremia within 30 days of completion of therapy. Deep seated infection was defined as: endocarditis, epidural abscess, pneumonia, psoas abscess, osteomyelitis, septic arthritis, or cardiac device infection. Data were analyzed using multivariate logistic regression with interaction variables.

Results: 328 cases of SAB were identified from 1/2010 to 7/2012, 31% were due to methicillin resistant S. aureus (MRSA). 16% of cases met failure criteria and 53% were complicated by deep seated infection. The following variables were independently associated with failure: age (aOR = 1.03, p<0.003); MRSA (aOR = 2.28, p=0.02); presence of deep seated infection (aOR = 2.97, p=0.04); and number of days with fever (aOR = 1.15, p=0.003).  Elevated vancomycin MIC was not predictive of failure (aOR Etest =1.32, p=0.62, aOR Phoenix = 1.01, p=0.99). No evidence of interaction between elevated MIC and deep seated infection was observed with Etest or Phoenix. 

Conclusion: We found no evidence of interaction between elevated vancomycin MIC and deep seated infection in relation to failure in SAB. Age, MRSA, presence of deep seated infection, and number of days with fever were independent predictors of failure.

Robert Odrobina, MD1, Peter S. Jones, MSLS2, Diana Handrahan, BS3, Jana Coombs, BS2, Bert K. Lopansri, MD2, Michaela Gazdik, PhD2 and Edward Stenehjem, MD, MSc4, (1)Division of Infectious Diseases, University of Utah, Salt Lake City, UT, (2)Clinical Epidemiology and Infectious Diseases, Intermountain Medical Center, Murray, UT, (3)Office of Research, Lds Hospital, Intermountain Healthcare, Salt Lake City, UT, (4)Division of Infectious Diseases, Intermountain Medical Center, Murray, UT


R. Odrobina, None

P. S. Jones, None

D. Handrahan, None

J. Coombs, None

B. K. Lopansri, None

M. Gazdik, None

E. Stenehjem, None

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