Risk Factors for and Outcomes of Bacteremia Caused by Extended-Spectrum ß-Lactamase-Producing Escherichia coli and Klebsiella Species at a Canadian Tertiary Care Hospital.

Background: Antimicrobial resistance due to production of extended-spectrum ß-lactamases by Escherichia coli and Klebsiella species (ESBL-EK) is concerning. Previous studies have shown that bacteremia due to ESBL-producing organisms is associated with increases in length of stay and/or mortality rate. Rates of infection by ESBL-EK vary worldwide, and regional differences in the prevalence of risk factors are likely. Few Canadian studies assessing risk factors for ESBL-EK infections or the outcomes of empiric therapy have been published.

Objectives: To determine risk factors for and patient outcomes associated with ESBL-EK bacteremia. The appropriateness of empiric antibiotic therapy and the effect of inappropriate empiric therapy on these outcomes were also examined.

Methods: In a retrospective, 1:1 case-control study conducted in a tertiary care hospital between 2005 and 2010, data for 40 patients with ESBL-EK bacteremia were compared with data for 40 patients who had non-ESBL-EK bacteremia.

Results: Of all variables tested, only antibiotic use within the previous 3 months was found to be an independent risk factor for acquisition of ESBL-EK bacteremia (odds ratio 5.2, 95% confidence interval 1.6-16.9). A greater proportion of patients with non-ESBL-EK bacteremia received appropriate empiric therapy (88% [35/40] versus 15% [6/40], p < 0.001). Time to appropriate therapy was longer for those with ESBL-EK bacteremia (2.42 days versus 0.17 day, p < 0.001). Patient outcomes, including length of stay in hospital, admission to the intensive care unit (ICU), length of stay in the ICU (if applicable), and in-hospital mortality were not affected by the presence of ESBL-EK or the appropriateness of empiric therapy.

Conclusions: Previous antibiotic use was a significant, independent risk factor for acquiring ESBL-EK. Thus, prior antibiotic use is an important consideration in the selection of empiric antibiotic therapy and should increase the concern for resistant pathogens.