EC 56 - Troubled Waters: Making Sense of Pseudomonas in a Neonatal Intensive Care Unit

Background: Pseudomonas aeruginosa (PA) is a resilient environmental bacterium commonly associated with healthcare-associated infections. Contaminated water sources, faucets, drains and moisture rich environments such as ventilators and contaminated equipment have been associated with PA outbreaks. Following a PA-infection related death of a neonatal intensive care unit (NICU) patient, we initiated an investigation to determine potential sources of the infection and develop a response plan.

Methods: Epidemiological case review was performed to guide environmental sampling. We tested mother's breast milk, high-risk equipment and water sources including breast milk pump parts, ventilator, isolette humidifier reservoir and sinks on the unit. A commercial vendor provided water microbiological analyses for PA on every sink. Speciation and phylogenetic relatedness were analyzed by high-resolution short read whole genome sequencing (WGS) on positive samples.

Results: PA was isolated from 18 of 21 drain (85.7%). No PA was isolated from sampled equipment. Water from the sink closest to the patient yielded PA (120 CFU/mL). PA was not detected in any other water samples (n=20). PA isolates from the drain and water were compared to the clinical isolate by WGS and found to be genomically unrelated. Faucet fixtures of impacted sink were replaced. Subsequent testing did not yield further positive PA cultures. No additional clinical cases were identified.

Conclusions: The lack of genomic relatedness of the contaminated sink and patient's PA suggests they were not linked. However, the proximity of the contaminated sink to the case makes this an epidemiologically plausible source of infection. The possibility exists that multiple strains of PA may have existed within the cultures collected, and therefore the lack of genomic relatedness does not absolutely rule out the source. Water sources, particularly on units housing vulnerable patients, should be identified in water infection control risk assessments for inclusion in water management plans to be considered for frequent water testing.