Hospital Toilets and Drainage Systems As a Reservoir for a Long-term Polyclonal Outbreak of Clinical Infections with Multidrug-resistant Species Complex

Background: Nosocomial outbreaks with multidrug-resistant bacteria with a probable reservoir in hospital toilets and drainage systems have been increasingly reported.

Aim: To investigate an increase in bacteraemia with extended-spectrum β-lactamase (ESBL)-producing at our hospital in 2021; the epidemiology of the outbreak suggested an environmental source.

Methods: Available clinical isolates from patient with infection or rectal carriage from 2019 to 2022 were collected. Clinical information was gathered from included patients and sampled sinks, shower drains, and toilet water. Short- and long-read whole-genome sequencing (WGS) was performed on patient and environmental isolates to assess phylogenetic relationships, antibiotic resistance genes/mutations, and plasmid profiles.

Results: WGS revealed four clusters and a polyclonal population consisting of ESBL-producing and . All clusters contained both clinical and environmental isolates. The environmental sampling revealed widespread contamination of the outbreak strains in the outbreak ward, and plasmid analyses indicated possible transfer of plasmids between species and clones. Most environmental findings in the outbreak ward were from toilet water, and enhanced cleaning of bathrooms and toilets was introduced. The following year, a decrease in outbreak strains in systemic infections was observed.

Conclusion: This investigation uncovered a polyclonal outbreak of multidrug-resistant and and unveiled a persistent reservoir of outbreak clones in the drainage system and toilet water, facilitating exchange of resistance genes. The risk of toilet water as a source of clinical infections warrants further investigation.