Chloramphenicol resistance in vancomycin-resistant enterococcal bacteremia: Impact of priop fluoroquinolone use?

OBJECTIVE: The prevalence of vancomycin-resistant enterococci (VRE) has increased markedly during the past decade. Few data exist regarding the epidemiology of resistance of VRE to chloramphenicol, one of the few therapeutic options. DESIGN: Survey and case-control study. SETTING: A 725-bed, tertiary-care academic medical center and a 344-bed urban community hospital. PATIENTS: Hospitalized patients with blood cultures demonstrating VRE. METHODS: We examined the trends in the prevalence of chloramphenicol resistance in VRE blood isolates at our institution from 1991 through 2002 and conducted a case-control study to identify risk factors for chloramphenicol resistance among these isolates. RESULTS: From 1991 through 2002, the annual prevalence of chloramphenicol-resistant VRE increased from 0% to 12% (P <.001, chi-square test for trend). Twenty-two case-patients with chloramphenicol-resistant VRE bloodstream isolates were compared with 79 randomly selected control-patients with chloramphenicol-susceptible VRE. Independent risk factors for chloramphenicol-resistant VRE were prior chloramphenicol use (odds ratio [OR], 10.9; 95% confidence interval [CI95], 1.72-68.91; P =.01) and prior fluoroquinolone use (OR, 4.74; CI95, 1.15-19.42; P =.03). Chloramphenicol-resistant VRE isolates were more likely to be susceptible to beta-lactams and resistant to tetracycline than were chloramphenicol-susceptible VRE isolates. CONCLUSIONS: Significant increases in the prevalence of chloramphenicol-resistant VRE may limit the future utility of chloramphenicol in the treatment of VRE infections, and close monitoring of susceptibility trends should continue. The association between fluoroquinolone use and chloramphenicol-resistant VRE, reflecting possible co-selection of resistance, suggests that recent dramatic increases in fluoroquinolone use may have broader implications than previously recognized.