Extended-Spectrum β-Lactamase–ProducingEscherichia coliandKlebsiellaSpecies: Risk Factors for Colonization and Impact of Antimicrobial Formulary Interventions on Colonization Prevalence

Abstract

Objective:The incidence of extended-spectrum β-lactamase (ESβL)–mediated resistance has increased markedly during the past decade. Risk factors for colonization with ESβL-producingEscherichia coliand Klebsiella species(ESβL-EK) remain unclear, as do methods to control their further emergence.Design:Case–control study.Setting:Two hospitals within a large academic health system: a 725-bed academic tertiary-care medical center and a 344-bed urban community hospital.Patients:Thirteen patients with ESβL-EK fecal colonization were compared with 46 randomly selected noncolonized controls.Results:Duration of hospitalization was the only independent risk factor for ESβL-EK colonization (odds ratio, 1.11; 95% confidence interval, 1.02 to 1.21). Of note, 8 (62%) of the patients had been admitted from another healthcare facility. In addition, there was evidence for dissemination of a singleK. oxytocaclone. Finally, the prevalence of ESβL-EK colonization decreased from 7.9% to 5.7% following restriction of third-generation cephalosporins (P= .51).Conclusions:ESβL-EK colonization was associated only with duration of hospitalization and there was no significant reduction following antimicrobial formulary interventions. The evidence for nosocomial spread and the high percentage of patients with ESβL-EK admitted from other sites suggest that greater emphasis must be placed on controlling the spread of such organisms within and between institutions.