Real-World Experience with Echinocandin MICs against Candida Species in a Multicenter Study of Hospitals That Routinely Perform Susceptibility Testing of Bloodstream Isolates
ABSTRACTReference broth microdilution methods ofCandidaechinocandin susceptibility testing are limited by interlaboratory variability in caspofungin MICs. Recently revised Clinical and Laboratory Standards Institute (CLSI) breakpoint MICs for echinocandin nonsusceptibility may not be valid for commercial tests employed in hospital laboratories. Indeed, there are limited echinocandin susceptibility testing data from hospital laboratories. We conducted a multicenter retrospective study of 9 U.S., Australian, and New Zealand hospitals that routinely testedCandidabloodstream isolates for echinocandin susceptibility from 2005 to 2013. Eight hospitals used Sensititre YeastOne assays. TheCandidaspp. wereC. albicans(n= 1,067),C. glabrata(n= 911),C. parapsilosis(n= 476),C. tropicalis(n= 185),C. krusei(n= 104), and others (n= 154). Resistance and intermediate rates were ≤1.4% and ≤3%, respectively, for each echinocandin againstC. albicans,C. parapsilosis, andC. tropicalis. Resistance rates amongC. glabrataandC. kruseiisolates were ≤7.5% and ≤5.6%, respectively. Caspofungin intermediate rates amongC. glabrataandC. kruseiisolates were 17.8% and 46.5%, respectively, compared to ≤4.3% and ≤4.4% for other echinocandins. Using CLSI breakpoints, 18% and 19% ofC. glabrataisolates were anidulafungin susceptible/caspofungin nonsusceptible and micafungin susceptible/caspofungin nonsusceptible, respectively; similar discrepancies were observed for 38% and 39% ofC. kruseiisolates. If only YeastOne data were considered, interhospital modal MIC variability was low (within 2 doubling dilutions for each agent). In conclusion, YeastOne assays employed in hospitals may reduce the interlaboratory variability in caspofungin MICs againstCandidaspecies that are observed between reference laboratories using CLSI broth microdilution methods. The significance of classifying isolates as caspofungin intermediate and anidulafungin/micafungin susceptible will require clarification in future studies.