Determinants of fluconazole resistance and echinocandin tolerance in isolates causing a large clonal candidemia outbreak among COVID-19 patients in a Brazilian ICU.

Patients presenting with severe COVID-19 are predisposed to acquire secondary fungal infections such as COVID-19-associated candidemia (CAC), which are associated with poor clinical outcomes despite antifungal treatment. The extreme burden imposed on clinical facilities during the COVID-19 pandemic has provided a permissive environment for the emergence of clonal outbreaks of multiple species, including and . Here we report the largest clonal CAC outbreak to date caused by fluconazole resistant (FLZR) and echinocandin tolerant (ECT) . Sixty strains were obtained from 57 patients at a tertiary care hospital in Brazil, 90% of them were FLZR and ECT. Although only 35.8% of FLZR isolates contained an mutation, all of them contained the mutation and significantly overexpressed . Introduction of into a susceptible background increased the MIC of fluconazole and voriconazole 8-fold and resulted in significant basal overexpression of . Additionally, FLZR isolates exclusively harboured E1939G outside of Fks1 hotspot-2, which did not confer echinocandin resistance, but significantly increased ECT. Multilocus microsatellite typing showed that 51/60 (85%) of the FLZR isolates belonged to the same cluster, while the susceptible isolates each represented a distinct lineage. Finally, biofilm production in FLZR isolates was significantly lower than in susceptible counterparts Suggesting that it may not be an outbreak determinant. In summary, we show that and confer FLZR and ECT, respectively, in CAC-associated . Our study underscores the importance of antifungal stewardship and effective infection control strategies to mitigate clonal outbreaks.