Pseudomonas aeruginosa carriage, colonization, and infection in ICU patients

We evaluated whether Pseudomonas aeruginosa associated nosocomial infections in our ICU originate mainly from patients' endogenous flora or from exogenous cross-transmission.

A 6-month prospective surveillance survey was performed according to standardized protocols at the interdisciplinary ICU of the Azienda Ospedaliera Cannizzaro.

The study analyzed 121 patients and focused on three different states: carriage upon admission, colonization of sterile sites, and infections during ICU stay.

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.

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.