Tracking the spread routes of opportunistic premise plumbing pathogens in a haematology unit with water points-of-use protected by antimicrobial filters.

Background: Water networks in hospitals are frequently contaminated by opportunistic premise plumbing pathogens (OPPPs) leading to installation of antimicrobial filters on water points-of-use (POU) in order to limit patients' exposure.

Aim: To assess the spread of OPPPs through secondary water routes (outside the plumbing system) in an adult haematology unit in which 52 out of 73 water POU were high risk for patients and protected by antimicrobial filters.

Methods: An observational audit identified six secondary water routes for which bacteria tracking and typing were performed in 315 surface samplings. Bacterial isolates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and compared to the infra-species level by multiplex repetitive element sequence-based polymerase chain reaction and/or by restriction fragment length polymorphism in pulse-field gel electrophoresis.

Findings: Pseudomonas aeruginosa and Stenotrophomonas maltophilia, as well as non-pathogenic OPPP indicators, were detected in water collected upstream of antimicrobial filters. P. aeruginosa was the sole OPPP retrieved from tested surfaces (5.1%). The same clone of P. aeruginosa spread from water source to dry surfaces in the same room and cross-contaminated two sinks in different rooms. Three clones of non-pathogenic OPPP indicators spread more widely in different rooms.

Conclusion: A strategy based on filtration of most (but not all) water POU in a haematology unit could be sufficient to limit the spread of OPPPs to the environment, provided a functional mapping of 'high-risk' POU has been undertaken. The residual spread of OPPPs and OPPP indicators linked to non-filtered water POU argues for careful monitoring of non-filtered water use.