Residual risk of Pseudomonas aeruginosa waterborne contamination in intensive care unit despite the presence of filters on all water points-of-use.

To assess the residual risk of waterborne contamination by Pseudomonas aeruginosa (PA) from water network colonized by a single genotype (Sequence Type (ST)299) despite the presence of antimicrobial filters in a medical intensive care unit (ICU). During the first 19-month period after ICU opening, water network contamination was assessed monthly by collecting water upstream the filters. Downstream water was also sampled to assess filters efficiency. PA clinical isolates from patients were collected and compared to the waterborne ST299-PA by multiplex-rep PCR, Pulsed-Field Gel Electrophoresis (PFGE) and whole-genome sequencing. Cross-transmission events occurring independently of the genotype of PA involved were also assessed. From 449 samples of filtered water, 1.3% were positive for PA in inoculum varying between 1 to 10 Antimicrobial filters are not sufficient to preserve patients from waterborne pathogens when the water network is highly contaminated. The microbiological survey of filtered water may be needed in units hosting at-risk patients for PA infections, even when all water points-of-use are protected by filters.

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