Résumé : OBJECTIVES: To determine the frequency of colonization by Enterobacter aerogenes in patients in the intensive care unit (ICU) for more than 48 hours and to evaluate the risk factors for infection in patients colonized by this bacteria. DESIGN: An 8-month prospective study. SETTING: A 12-bed medical-surgical ICU in a 450-bed, university-affiliated, tertiary-care hospital in Belgium. METHOD: Pulsed-field gel electrophoresis was used to determine the genotypes of E. aerogenes isolates. RESULTS: We observed two major clones of E. aerogenes in the ICU. Interestingly, 87.5% of infected patients had the same genomic profile for colonization and infection. Risk factors for infection in this particular population included younger age, prolonged hospital stay, mechanical ventilation, and bronchoscopy. CONCLUSIONS: Colonization is a major prerequisite for infection. The identification of risk factors for infection in colonized patients can optimize the quality of treatment in the ICU. © 2002 Society for Healthcare Epidemiology of America.