Besides, all previously known risk factors were adjusted for, as well as widespread and repeated patient and tap water screening (including samples from shared rooms), which have not always been completely (only patient-to-patient transmission) [11,18] or properly (type and frequency of environmental screening) [10,13] selleck chemical assessed. Moreover, active antibiotics were distinguished from inactive antibiotics (selective antibiotic pressure), which could help P. aeruginosa become dominant in the patients’ flora.In our ICU, as potentially in others with the same endemic and antibiotic consumption profiles, the results of this study will lead to the development of coordinated strategies against the use of antibiotics that are inactive against P.

aeruginosa (such as a decrease in systematic penicillin or cephalosporin treatment for aspiration pneumonia) and against the environmental spread of bacteria. The latter should include alcohol-based hand-cleaning programmes since cross-contamination between patients and contaminated tap water was suspected in our study. Contaminated tap water and patients’ samples were associated with P. aeruginosa acquisition in univariate analysis but only patients’ samples were significant in multivariate analysis. Positive cultures from shared rooms were associated with P. aeruginosa acquisition in univariate analysis and should be interpreted as additional to ICU P. aeruginosa colonization pressure.There are several limitations to our study. It was a single-centre study and the limited observations may give reduced power to detect other contributing risk factors.

These limitations prevent its application to other ICUs where the patient case mix, prevalence of P. aeruginosa colonization at admission and antibiotic consumption are different. Antibiotic selective pressure could have played a role in revealing a pre-existing P. aeruginosa flora shared with the patient’s environment without a cause-and-effect relationship (which would only have been demonstrated by chronological acquisition of the same genotypic strain) or in rendering the patient susceptible to P. aeruginosa acquisition from the environment. Other limitations include the fact that adherence to hygiene rules was not assessed, antibiotic consumption before admission was not recorded and P. aeruginosa screening was not performed at the end of the ICU stay.

Moreover, the environment (patients and tap water) was screened by intermittent samples. However, the inclusion in the model of the most recent sample provided a closer analysis of the time-dependent process of acquisition. Finally, routine surveillance cultures were not obtained from 15 patients AV-951 with a short stay, although this probably did not significantly influence our findings as they accounted for only 7% of total patient-days.