Extended-spectrum β-lactamases:: Frequency, risk factors, and outcomes

Study Objective. To determine epidemiologic factors of extended-spectrum beta -lactamase (ESBL)-producing Escherichia coli or Klebsiella pneumoniae in a nonoutbreak setting. Design. Retrospective analysis. Setting. University teaching hospital. Patients. Fifty-seven patients with cultures of presumed ESBL-producing (i.e., ceftazidime-resistant) E. coli or K. pneumoniae. Interventions. To determine overall frequency, institutional antibiograms from 1991-1999 were examined for percentage of isolates with ceftazidime resistance. Medical records from January 1997-June 2000 were reviewed for patient demographics, comorbidities, culture site, antimicrobial therapy, and clinical and microbiologic outcomes. Measurements and Main Results. From 1991-1999, frequency increased from undetectable to 4% for ceftazidime-resistant E. coli and from 2% to 6% for ceftazidime-resistant K. pneumoniae. Seventy-one isolates were identified in the 57 patients with presumed ESBL-producing E. coli or K. pneumonia. Fifty-one isolates (72%) were E. coli, with urine the primary site of infection (62%). Eighty-six percent of patients had known risk factors for infection due to ESBL-producing organisms, including hospitalization (37 patients) and residence in long-term care facilities (12 patients). However, in 14% (8 patients), the infection was community acquired in patients who resided at home. Conclusion. In addition to known populations at risk, ambulatory patients with chronic conditions represent another patient population that may harbor ESBL-producing organisms.