Cross-contamination of carbapenem-resistant Gram-negative bacteria between patients and hospital environment in the first year of a newly built surgical ward

BACKGROUND: Transmission and outbreaks of carbapenem-resistant gram-negative (CRGN) bacteria in hospitals are often associated with contamination of the wastewater environment. We performed a prospective observational study to investigate the colonisation of the hospital wastewater environment during the first year of occupancy of the surgical intermediate and intensive care units of a newly constructed building at the University Hospital of Heidelberg, Germany.

METHODS: We performed monthly screening of the wastewater system (toilets and sinks) for 12 months, starting one month before opening (1 October 2020 to 30 October 2021). Admission and weekly rectal screening of patients for CRGN were also performed in parallel. Bacterial isolates were characterised by whole genome sequencing.

RESULTS: 27 of 1978 (1.4%) admitted patients were colonised/infected with CRGN. A total of 29 CRGN isolates from 24 patients and 52 isolates were available for sequencing. Within the first month of occupancy, we identified seven patients colonised/infected with CRGN, while none were found in the environmental reservoirs. The first detection of CRGN isolates in the sewage system started five months after the first occupancy. Two previously non-colonised patients were colonised/infected with Pseudomonas aeruginosa strains colonising the sewage system. The significant identity of plasmids carrying the carbapenemase gene suggests that long-term colonisation of the sewage system facilitates the emergence of new carbapenem-resistant clones.

INTERPRETATION: Cross-contamination between patients and the hospital environment is bidirectional. Our study demonstrated that contamination of the hospital wastewater environment may lead to persistent colonisation and may serve as a reservoir for nosocomial acquisition of CRGN.