In vivo evolution to echinocandin resistance and increasing clonal heterogeneity in during a difficult-to-control hospital outbreak, Italy, 2019 to 2022.

A difficult-to-control outbreak of is ongoing in a large tertiary care hospital in Liguria, Italy, where it first emerged in 2019. In a retrospective analysis, 503 cases of carriage or infection were observed between July 2019 and December 2022. Genomic surveillance identified putative cases that no longer occurred as part of one defined outbreak and the emergence of echinocandin (pandrug) resistance following independent selection of S639F and F635Y mutants upon prolonged exposure to caspofungin and/or anidulafungin.