Extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella species:: Risk factors for colonization and impact of antimicrobial formulary interventions on colonization prevalence

OBJECTIVE: The incidence of extended-spectrum beta-lactamase (ESbetaL)-mediated resistance has increased markedly during the past decade. Risk factors for colonization with ESbetaL-producing Escherichia coli and Klebsiella species (ESbetaL-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 ESbetaL-EK fecal colonization were compared with 46 randomly selected noncolonized controls. RESULTS: Duration of hospitalization was the only independent risk factor for ESbetaL-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 single K. oxytoca clone. Finally, the prevalence of ESbetaL-EK colonization decreased from 7.9% to 5.7% following restriction of third-generation cephalosporins (P = .51). CONCLUSIONS: ESbetaL-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 ESbetaL-EK admitted from other sites suggest that greater emphasis must be placed on controlling the spread of such organisms within and between institutions (Infect Control Hosp Epidemiol 2002;23:254-260).