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 β-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.