Ecology of Pseudomonas aeruginosa in the intensive care unit and the evolving role of water outlets as a reservoir of the organism

In spite of the significant changes in the spectrum of organisms causing intensive care unit (ICU)-associated infections, Pseudomonas aeruginosa has held a nearly unchanged position in the rank order of pathogens causing ICU-related infections during the last 4 decades. Horizontal transmissions between patients have long been considered the most frequent source of P aeruginosa colonizations/infections. The application of molecular typing methods made it possible, during the last ∼7 years, to identify ICU tap water as a significant source of exogenous P aeruginosa isolates. A review of prospective studies published between 1998 and 2005 showed that between 9.7% and 68.1% of randomly taken tap water samples on different types of ICUs were positive for P aeruginosa, and between 14.2% and 50% of infection/colonization episodes in patients were due to genotypes found in ICU water. Faucets are easily accessable for preventive measures, and the installation of single-use filters on ICU water outlets appears to be an effective concept to reduce water-to-patient transmissions of this important nosocomial pathogen.