Pseudomonas aeruginosa carriage, colonization, and infection in ICU patients.

Objective: We evaluated whether Pseudomonas aeruginosa associated nosocomial infections in our ICU originate mainly from patients' endogenous flora or from exogenous cross-transmission.
Design and Setting: A 6-month prospective surveillance survey was performed according to standardized protocols at the interdisciplinary ICU of the Azienda Ospedaliera Cannizzaro.
Patients: The study analyzed 121 patients and focused on three different states: carriage upon admission, colonization of sterile sites, and infections during ICU stay.
Results: We identified 138 P. aeruginosa isolates from 45 patients. The cumulative incidence of P. aeruginosa sustained colonization in the ICU was 29.9/100 patients, and the incidence density was 16.2/1,000 patient-days. The cumulative incidence of P. aeruginosa-sustained infections in the ICU was 36.7/100 patients, and the incidence density was 19.9/1,000 patient-days. The most frequent infection type was ventilator-associated pneumonia. PFGE analysis of P. aeruginosa isolates led to the identification of a major clone represented by 60.8% of isolates involving 45.9% of patients. The impact of cross-transmission, i.e., the preventable proportion of P. aeruginosa acquisition, was estimated to be at least 59.5% of all colonization or infection episodes. Acquisition of multidrug-resistant P. aeruginosa was significantly associated with cross-transmission.
Conclusions: Our results suggest that the ICU personnel and environment served as reservoirs for cross-transmission and emphasize the importance of exogenous acquisition of multidrug-resistant P. aeruginosa, of reduction in antibiotic pressure, and prompt enforcement of infection control measures.