Large, protracted, multi-species and multi-clonal spread of VIM-type metallo-β-lactamase-producing Enterobacterales in an Italian hospital.

Carbapenem-resistant Enterobacterales, particularly those producing carbapenemase (CPE), pose a major threat to human health, being listed among critical-priority resistant pathogens by the World Health Organization. To report on a large nosocomial spread of CPE of different species producing Verona integron-encoded metallo-β-lactamase (VIM)-type carbapenemases, and on the infection prevention and control measures that were adopted to combat the spread. Conventional culture and molecular methods were used for detection and identification of VIM-positive CPE (VIM-CPE) causing infections or colonizing patients or present in environmental specimens. Whole-genome sequencing analysis of selected isolates was performed to investigate clonal relatedness. Basic (active surveillance, contact precautions, close contact screening, cohorting of patients, surface cleaning, hand hygiene) and advanced (weekly point-prevalence surveys for rectal colonization, additional training of healthcare workers, extraordinary ward sanitization, extraordinary maintenance interventions, and environmental microbiological screening, single-use equipment, ward relocation) infection prevention and control (IPC) measures were implemented to combat the spread. Spread of VIM-CPE involving 151 patients (mostly colonizations) was documented in a single hospital ward from November 2021 to December 2023. The spread involved several different species of Enterobacterales, with clonal expansion documented in some cases. Implementation of basic and advanced IPC measures was temporarily successful at mitigating the spread, but multiple relapses were observed, suggesting the presence of an unidentified environmental reservoir. VIM-CPE has the potential to cause large and complex nosocomial outbreaks in hospital environments, underscoring the challenges to their control by IPC practices.