Patients were excluded from the study for the following reasons: age less than 18 years, polymicrobial infection (blood culture positive for more than one pathogen), neutropenia (white blood cell count less than 1.0 x 109/L), or death prior to the return of positive blood cultures. In order to preserve the independence of observations, only the initial episode of gram negative bacteremia was included in the analysis (e.g., patients were only included once). The study was approved by the Duke University Medical Center Institutional Review Board.