title: Risk factors for increasing multidrug resistance among extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella species.
abstract: BACKGROUND
  The importance of infections due to extended-spectrum beta -lactamase-producing Escherichia coli and Klebsiella species (ESBL-EK) has been increasingly recognized in recent years. ESBL-EK infections are of clinical concern, because few antimicrobials are available as therapeutic options. Increased reliance on carbapenems has led to increasing carbapenem resistance. Efforts to maintain current therapeutic options for ESBL-EK infections are essential.
  
  
  METHODS
  We conducted a case-control study to identify risk factors for multidrug resistance (MDR) among ESBL-EK. All patients at our institution who had an inpatient clinical culture result positive for an ESBL-EK during the period of 1 June 1997 through 31 December 2002 were eligible for inclusion. An MDR ESBL-EK was defined as ESBL-EK demonstrating resistance to trimethoprim-sulfamethoxazole, aminoglycosides, and quinolones. All available ESBL-EK isolates were characterized by pulsed-field gel electrophoresis (PFGE).
  
  
  RESULTS
  Of 361 total ESBL-EK isolates, 68 (18.8%) were MDR. During the study period, the prevalence of MDR among ESBL-EK isolates increased from 12.5% to 26.9%. The only independent risk factor for MDR ESBL-EK was the infecting organism (i.e., Klebsiella pneumoniae; adjusted odds ratio, 11.7; 95% confidence interval, 4.77-28.51; P < .001). Prior antibiotic use was not independently associated with MDR ESBL-EK. PFGE patterns from K. pneumoniae isolates indicated close genetic relatedness among a substantial proportion of isolates.
  
  
  CONCLUSIONS
  The emergence of MDR among ESBL-EK has important implications for the future ability to treat these infections. The strong association between the species of infecting organism and MDR suggests that the epidemiology in K. pneumoniae may be unique. PFGE results suggest that horizontal spread is important in the emergence of MDR ESBL-EK.
authors.affiliation: Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6021, USA.
authors.forename: Emily P
authors.initials: EP
authors.lastname: Hyle
authors.forename: Adam D
authors.initials: AD
authors.lastname: Lipworth
authors.forename: Theoklis E
authors.initials: TE
authors.lastname: Zaoutis
authors.forename: Irving
authors.initials: I
authors.lastname: Nachamkin
authors.forename: Neil O
authors.initials: NO
authors.lastname: Fishman
authors.forename: Warren B
authors.initials: WB
authors.lastname: Bilker
authors.forename: Xiangquin
authors.initials: X
authors.lastname: Mao
authors.forename: Ebbing
authors.initials: E
authors.lastname: Lautenbach
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016022:Case-Control Studies; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology; D005260:Female; D006801:Humans; D007709:Klebsiella / Q000201:enzymology* / Q000235:genetics; D007710:Klebsiella Infections / Q000453:epidemiology / Q000382:microbiology; D008297:Male; D008875:Middle Aged; D010802:Phylogeny; D012307:Risk Factors; D013997:Time Factors; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001618:beta-Lactamases