Rising incidence of carbapenem-resistant <i>Citrobacter</i> spp. in a German tertiary-care hospital: epidemiology, clinical impact, and the role of the hospital wastewater system—findings from a six-year molecular study

In this study, we analyzed the significant increase in CRC strains at our tertiary-care hospital over the past six years. Our findings revealed that, unlike classical outbreak scenarios - typically characterized by the clonal expansion of one strain within a single ward or unit - the rising incidence of CRC was driven by the dissemination of numerous genetically diverse strains across multiple departments. The hospital sewage system was identified as a reservoir and plays an important role in the rapid proliferation and dissemination of CRC. The high complexity of the situation presents a new challenge, as transmission pathways are now difficult to trace, hindering effective prevention. Remarkably, the majority of patients affected by CRC were merely colonized, and severe infections were not observed. It remains to be determined whether this pattern reflects a site-specific phenomenon or indicates a broader trend on a European or even global scale.