A persistent sink reservoir as a potential source of Pseudomonas aeruginosa infections in pediatric oncology patients.

Objective: Outbreaks of Pseudomonas aeruginosa infections have been linked to water-related sources. We describe the investigation of a suspected outbreak of five P. aeruginosa infections in pediatric oncology patients in 2021 that triggered a retrospective review and prospective monitoring of additional cases, environmental sampling, and bacterial genomic analysis.

Setting and patients: Pediatric oncology center.

Methods: Medical records of patients with P. aeruginosa were reviewed and staff were interviewed to identify common exposures. Environmental samples were cultured for P. aeruginosa. Patient and environmental isolates underwent whole genome sequencing and core genome multi-locus sequence typing (cgMLST) and sequences were added to a previously existing library of P. aeruginosa clinical isolates collected in 2017 and onwards to determine strain relatedness.

Findings: During 2019-2022, 82 patients with 110 episodes of P. aeruginosa infections were identified and 132 isolates of P. aeruginosa were sequenced. Twenty-three environmental samples were collected, of which two grew P. aeruginosa in culture. CgMLST demonstrated four multi-patient isolate clusters but no genetic relatedness among the isolates from the patients in the suspected outbreak. Two sink-derived isolates from 2021 were genetically related to patient-derived isolates from 2018 and 2017.

Conclusions: Sequencing revealed there is no common source or linkage between the isolates of the suspected P. aeruginosa outbreak in 2021. However, it revealed genetic relatedness of previous patient strains to later strains collected from hospital sinks, suggesting persistent colonization of a reservoir with P. aeruginosa.