title: Risk factors, molecular epidemiology and outcomes of ertapenem-resistant, carbapenem-susceptible Enterobacteriaceae: a case-case-control study.
abstract: BACKGROUND
  Increasing prevalence of ertapenem-resistant, carbapenem-susceptible Enterobacteriaceae (ERE) in Singapore presents a major therapeutic problem. Our objective was to determine risk factors associated with the acquisition of ERE in hospitalized patients; to assess associated patient outcomes; and to describe the molecular characteristics of ERE.
  
  
  METHODS
  A retrospective case-case-control study was conducted in 2009 at a tertiary care hospital. Hospitalized patients with ERE and those with ertapenem-sensitive Enterobacteriaceae (ESE) were compared with a common control group consisting of patients with no prior gram-negative infections. Risk factors analyzed included demographics; co-morbidities; instrumentation and antibiotic exposures. Two parallel multivariate logistic regression models were performed to identify independent variables associated with ERE and ESE acquisition respectively. Clinical outcomes were compared between ERE and ESE patients.
  
  
  RESULTS
  Twenty-nine ERE cases, 29 ESE cases and 87 controls were analyzed. Multivariate logistic regression showed that previous hospitalization (Odds ratio [OR], 10.40; 95% confidence interval [CI], 2.19-49.20) and duration of fluoroquinolones exposure (OR, 1.18 per day increase; 95% CI, 1.05-1.34) were unique independent predictors for acquiring ERE. Duration of 4(th)-generation cephalosporin exposure was found to predict for ESE acquisition (OR, 1.63 per day increase; 95% CI, 1.05-2.54). In-hospital mortality rates and clinical response rates were significantly different between ERE and ESE groups, however ERE infection was not a predictor of mortality. ERE isolates were clonally distinct. Ertapenem resistance was likely to be mediated by the presence of extended-spectrum β-lactamases or plasmid-borne AmpC in combination with impermeability due to porin loss and/or efflux pumps.
  
  
  CONCLUSIONS
  Prior hospitalization and duration of fluoroquinolone treatment were predictors of ERE acquisition. ERE infections were associated with higher mortality rates and poorer clinical response rates when compared to ESE infections.
authors.affiliation: Department of Pharmacy, Singapore General Hospital, Singapore, Singapore.
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Teo
authors.forename: Yiying
authors.initials: Y
authors.lastname: Cai
authors.forename: Sarah
authors.initials: S
authors.lastname: Tang
authors.forename: Winnie
authors.initials: W
authors.lastname: Lee
authors.forename: Thean Yen
authors.initials: TY
authors.lastname: Tan
authors.forename: Thuan Tong
authors.initials: TT
authors.lastname: Tan
authors.forename: Andrea Lay-Hoon
authors.initials: AL
authors.lastname: Kwa
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use; D015780:Carbapenems / Q000494:pharmacology / Q000627:therapeutic use*; D016022:Case-Control Studies; D003428:Cross Infection / Q000188:drug therapy* / Q000453:epidemiology / Q000382:microbiology; D004352:Drug Resistance, Microbial; D024901:Drug Resistance, Multiple, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000254:growth & development; D004756:Enterobacteriaceae Infections / Q000188:drug therapy* / Q000453:epidemiology / Q000382:microbiology; D000077727:Ertapenem; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D017720:Molecular Epidemiology; D015999:Multivariate Analysis; D012307:Risk Factors; D012846:Singapore / Q000453:epidemiology; D016896:Treatment Outcome; D055815:Young Adult; D047090:beta-Lactams / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: D000900:Anti-Bacterial Agents; D015780:Carbapenems; D047090:beta-Lactams; D000077727:Ertapenem