Exogenous acquisition of Pseudomonas aeruginosa in intensive care units: a prospective multicentre study, DYNAPYO study.

Summary Pseudomonas aeruginosa remains one of the most common nosocomial pathogens in intensive care units (ICUs). Although exogenous acquisition has been widely documented in outbreaks, its importance is unclear in non-epidemic situations. We aimed to elucidate the role of exogenous origin of P. aeruginosa in ICU patients. We performed a chronological analysis of the acquisition of P. aeruginosa using samples collected in 2009 in DYNAPYO cohort study during which patients and tap water were weekly screened. Molecular relatedness of P. aeruginosa isolates was investigated by pulsed-field gel electrophoresis. Exogenous acquisition was defined as identification of a P. aeruginosa pulsotype previously isolated from another patient or tap water in the ICU. DYNAPYO cohort included 1,808 patients (10,402 samples) and 233 water taps (4,946 samples). Typing of 1,515 isolates from 373 patients and 375 isolates from 81 tap water samples identified 296 pulsotypes. Analysis showed an exogenous acquisition in 170 (45.6%) of 373 patients. The pulsotype identified was previously isolated from another patient and from a tap water sample for 86 and 29 patients respectively. The results differed according to the ICU. The exogenous acquisition of P. aeruginosa could be prevented in a half proportion of patients. The overall findings of this survey supports the need for studies on routes of transmission and risk assessment approach to better define how to control exogenous acquisition in ICUs.