Vancomycin-resistant Entorococcus faecium : a national prevalence study in Switzerland

Vancomycin-resistant Enterococcus faecium (VREfm) poses a growing threat to healthcare systems. In Switzerland, VREfm remains rare but appears to be on the rise. We aimed to assess the national prevalence of VREfm, identify major circulating clones, and explore evidence of clonal dissemination using genomic epidemiology. All Swiss diagnostic laboratories were invited to submit VREfm isolates collected during February–March 2024. Isolates underwent species confirmation, antimicrobial susceptibility testing, and whole-genome sequencing. Sequence types (STs), core genome multilocus sequence typing (cgMLST), and resistance gene profiles were determined. Clusters were defined based on allele distances. We analyzed 78 VREfm isolates from 17 cantons. Most carried the vanA gene (94%) and exhibited high-level resistance to vancomycin and teicoplanin; the remainder carried vanB. Two clones dominated: ST80 (n=43) and ST612 (n=14), both within clonal complex 17. Eight cgMLST-defined clusters were identified. The ST80-Q cluster was confined to a single canton and linked to a known outbreak. In contrast, ST612-C was found in 7 cantons, suggesting cryptic inter-cantonal dissemination. All ST612 isolates harbored liaR and liaS mutations associated with reduced daptomycin susceptibility, although phenotypic resistance was not observed. No resistance to linezolid or tigecycline was detected. This first nationwide genomic survey reveals the emergence and dissemination of dominant VREfm clones in Switzerland, particularly ST80 and ST612. The results highlight the need for national genomic surveillance and coordinated infection prevention strategies to detect and contain high-risk VREfm clones.