Large Outbreak in a Surgical Intensive Care Unit of Colonization or Infection withPseudomonas aeruginosathat Overexpressed an Active Efflux Pump

During a 30-month survey, 55 patients were colonized or infected by a single clone of Pseudomonas aeruginosa in a surgical intensive care unit (ICU). This clone overexpressed an efflux pump system, and its antibiotic resistance pattern was extremely stable as it spread from patient to patient. Pulsed-field gel electrophoresis showed that isolates from different patients were genetically identical or very similar. We were unable to identify an environmental reservoir, but cultures of hand specimens from 2 health care workers were positive. It was not clear whether this carriage was the source of the epidemic or a consequence of it. However, the propagation of the epidemic clone was probably linked to its transmission by the staff from patient to patient. The outbreak was controlled, with difficulty, by strengthening isolation procedures, replacing the antiseptic soap being used by the staff, and changing the antibiotic prescription policy. This observation emphasizes the importance of compliance with hand washing and universal precautions.