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

Objective 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). Methods 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. Results From 449 samples of filtered water, 1.3% were positive for PA in inoculum varying between 1 to 104 Colony Forming Unit (CFU)/100mL according to the tap. All PA hydric isolates belonged to PA-ST299 and displayed <2 Single Nucleotide Polymorphisms (SNPs). Among 278 clinical isolates from 122 patients, 10 isolates in 5 patients showed identical profiles to the hydric PA-ST299 clone in both multiplex-rep PCR and PFGE and differed by <5 SNPs on average, confirming the water network reservoir as the source of contamination by PA for 4.09% of patients. Cross-transmission events by other genotypes of PA than PA-ST299 were responsible for the contamination of 1.75 % of patients. Discussion/conclusion 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.