Ertapenem-Resistant Enterobacteriaceae: Risk Factors for Acquisition and Outcomes

BACKGROUND AND OBJECTIVE. Carbapenem resistance among Enterobacteriaceae is of concern because of increasing prevalence and limited therapeutic options. Limited research has been focused on understanding ertapenem resistance as a more sensitive marker for resistance to other carbapenems. We sought to determine risk factors for acquisition of ertapenem-resistant, meropenem-susceptible, or intermediate Enterobacteriaceae and to assess associated patient outcomes. DESIGN. Retrospective case-control study among adult hospitalized inpatients. SETTING. A 902-bed quaternary care urban hospital. RESULTS. Sixty-two cases of ertapenem-resistant Enterobacteriaceae were identified from March 14, 2006, through October 31, 2007, and 62 unmatched control patients were randomly selected from other inpatients with cultures positive for ertapenem-susceptible Enterobacteriaceae. Thirty-seven (60%) of case patient isolates were Enterobacter cloacae, 20 (32%) were Klebsiella pneumoniae, and 5 (8%) were other species of Enterobacteriaceae. Risk factors for ertapenem-resistant Enterobacteriaceae infection included intensive care unit stay (odds ratio [OR], 4.6 [95% confidence interval {CI}, 2.0-10.3]), vancomycin-resistant Enterococcus colonization (OR, 7.1 [95% CI, 2.4-21.4]), prior central venous catheter use (OR, 10.0 [95% CI, 3.0-33.1]), prior receipt of mechanical ventilation (OR, 5.8 [95% CI, 2.1-16.2]), exposure to any antibiotic during the 30 days prior to a positive culture result (OR, 18.5 [95% CI, 4.9-69.9]), use of a beta-lactam during the 30 days prior to a positive culture result (OR, 6.9 [95% CI, 3.0-16.0], and use of a carbapenem during the 30 days prior to a positive culture result (OR, 18.2 [95% CI, 2.6-130.0]). For the 62 case patients, 30-day outcomes from the time of positive culture result were 24 discharges (39%), 10 deaths (16%), and 28 continued hospitalizations (44%). The final end point of the hospitalization was discharge for 44 patients (71%) and death for 18 patients (29%). CONCLUSIONS. Ertapenem-resistant Enterobacteriaceae are important nosocomial pathogens. Multiple mechanisms of resistance may be in operation. Additional study of ertapenem resistance is needed.