Hospital water environment and antibiotic use: key factors in a nosocomial outbreak of carbapenemase Serratia marcescens

Background: The healthcare water environment is a potential reservoir of carbapenemresistant organisms (CROs). Aim: To report the role of the water environment as a reservoir and the infection control measures applied to suppress a prolonged outbreak of Klebsiella pneumoniae carbapenemase-producing Serratia marcescens (KPC-SM) in two intensive care units (ICUs). Methods: The outbreak occurred in the ICUs of a tertiary hospital from October 2020 to July 2021. Comprehensive patient contact tracing and environmental assessments were conducted, and a case-control study was performed to identify factors associated with the acquisition of KPC-SM. Associations among isolates were assessed via pulsed-field gel electrophoresis (PFGE). Antibiotic usage was analysed. Findings: The outbreak consisted of two waves involving a total of 30 patients with KPCSM. Multiple environmental cultures identified KPC-SM in a sink, a dirty utility room, and a communal bathroom shared by the ICUs, together with the waste bucket of a continuous renal replacement therapy (CRRT) system. The genetic similarity of the KPC-SM isolates from patients and the environment was confirmed by PFGE. A retrospective review of 30 cases identified that the use of CRRT and antibiotics was associated with acquisition of KPC-SM (P < 0.05). There was a continuous increase in the use of carbapenems; notably, the use of colistin has increased since 2019. Conclusion: Our study demonstrates that CRRT systems, along with other hospital water environments, are significant potential sources of resistant micro-organisms, underscoring the necessity of enhancing infection control practices in these areas. (c) 2024 The Healthcare Infection Society. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.