A Hospital Outbreak of High-level β-Lactam-Resistant Enterobacter spp.: Association more with Ampicillin and Cephalosporin Therapy than with Nosocomial Transmission

Abstract

We studied an 8 month outbreak of a 7-fold increased isolation rate of high-level β-lactam-resistant Enterobacter spp. from clinical infections (20 patients, 22 isolates: 20 E. cloacae, 2 E. aerogenes). In a case–control analysis the occurrence of resistant Enterobacter spp. was found to be associated with treatment with multiple antibiotics (p = 0.03), broad-spectrum β-lactam agents (p = 0.0001) including ampicillin (p = 0.04), and cephalosporins (cefuroxime and cefotaxime, p = 0.004). Biochemical fingerprinting and pulsed-field gel electrophoresis (PFGE) typing showed no identity between the resistant isolates, indicating that neither cross-infection nor nosocomial transmission from a common source was the immediate cause of the problem. The outbreak was not paralleled by the overall Enterobacter spp. isolation rate or the antibiotic usage pattern in the hospital. Thus, the underlying cause of the outbreak remained obscure.