Two clusters of carbapenemase-producing bacteria linked to hospital utility room wastewater drains – an outbreak report

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BACKGROUND: Outbreak investigations of two carbapenemase-producing bacteria (CPB)-clusters identified a link to utility room wastewater drains (URWD), prompting an investigation into CPB-colonization of the hospital's URWD and into utility room management to identify possible breaches in infection prevention and control (IPC) measures. METHODS: At the University Hospital Basel, Switzerland, a cluster of four patients with VIM-1-producing Enterobacter hormaechei and two patients with KPC-3-producing Citrobacter freundii, occurred between 07/2022 - 07/2024. A multidisciplinary team (IPC specialists, nurses, cleaning experts) evaluated utility room management. Wastewater drains in affected patient rooms and 25 utility rooms of the hospital building (including two wards in which the two transmission-cluster occurred) affected by the clusters were screened for CPB-colonization and whole genome sequencing was performed on clinical and environmental CPB isolates. RESULTS: gene corresponding to both clusters were identified in sequences of Citrobacter freundii and Klebsiella pneumoniae isolates colonizing the ward's URWD. Colonized drains were in proximity to affected patient's rooms, while none of the wastewater drains in the respective patient rooms was colonized with CPB. Overall, CPB were identified in 52% of all URWD. Several breaches in utility room management and design facilitating colonization with CPB and potentially leading to contamination of shared medical equipment by dispersal were observed, including lacking separation between clean and contaminated zones in utility rooms (34%), and improper use of contaminated zones for storage of clean shared medical equipment (88.7%). CONCLUSIONS: URWD serve as reservoirs for CPB. Breaches in utility room management and design, potentially leading to contamination of shared medical equipment by dispersal from contaminated wastewater drains, represent an intervention target for prevention of CPB-transmission.

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