Risk Factors for Infection or Colonization with CTX-M Extended-Spectrum β-Lactamase (ESBL)-Positive Escherichia coli

  1. Jennifer H. Han, MD, MSCE1,#,
  2. Kei Kasahara, MD2,
  3. Paul H. Edelstein, MD3,
  4. Warren B. Bilker, PhD4,5 and
  5. Ebbing Lautenbach, MD, MPH, MSCE1,4,5

+Author Affiliations

  1. 1Division of Infectious Diseases, Department of Medicine

  2. 3Department of Pathology and Laboratory Medicine

  3. 4Department of Biostatistics and Epidemiology

  4. 5Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, PA

  5. 2Center for Infectious Diseases, Nara Medical University, Kashihara, Japan


Background: There has been a significant increase in the prevalence of Enterobacteriaceae that produce CTX-M-type extended-spectrum β-lactamases. The objective of this study was to evaluate risk factors for infection or colonization with CTX-M-positive Escherichia coli.

Methods: A case-control study was conducted within a university system from January 1, 2007 to December 31, 2008. All patients with clinical cultures with E. coli demonstrating resistance to extended-spectrum cephalosporins were included. Case patients were designated as those with cultures positive for CTX-M-positive E. coli, and control patients as those with non-CTX-M-producing E. coli. Multivariable logistic regression analyses were performed to evaluate risk factors for CTX-M-positive isolates.

Results: 83 (56.8%) of a total of 146 patients had cultures with CTX-M-positiveE. coli. On multivariable analyses, there was a significant association between infection or colonization with CTX-M-type β-lactamase-positive E. coli and receipt of piperacillin-tazobactam in the 30 days prior to the culture date (odds ratio [OR], 7.36; 95% confidence interval [CI], 1.61-33.8; P=0.01) and a urinary culture source (OR, 0.36; 95% CI, 0.17-0.77; P=0.008). Rates of resistance to fluoroquinolones was significantly higher in isolates from case as opposed to control patients (90.4% and 50.8%, respectively; P<0.001).

Conclusions: We found that non-urinary sources of clinical cultures and the recent use of piperacillin-tazobactam conferred an increased risk of colonization or infection with CTX-M-positive E. coli. Future studies will need to focus on outcomes associated with infections due to CTX-M-positive E. coli, as well as infection control strategies to limit the spread of these increasingly common organisms.

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