Reservoirs of Pseudomonas aeruginosa in the intensive care unit. The role of tap water as a source of infection

In spite of significant changes in the spectrum of organisms causing nocosomial infections in intensive care units (ICUs), Pseudomonas aeruginosa has held a nearly unchanged position as an important pathogen. Today, the organism is isolated as the second most frequent organism causing ventilator-associated pneumonia, and the third or fourth most frequent pathogen causing septicemia, urinary tract infections, and surgical wound infections. In the past, horizontal transmissions were regarded as the most relevant route of strain acquisition. However, during the last 10 years, a significant proportion of P. aeruginosa isolates were demonstrated to stem from ICU water sites. Studies using molecular typing techniques have shown that up to 50% (in one study 92%) of nosocomial P. aeruginosa acquisitions may result from transmission through tap water. Additional proof of concept of waterborne infection comes from the reports of three recent studies that infection rates may be lowered significantly by eliminating colonized tap water sources or interrupting transmission chains from water sites.