The impact of new epidemiological cutoff values on Candida glabrata resistance rates and concordance between testing methods

Abstract

Interpretive criteria for Candida susceptibility testing were recently revised with the establishment of species-specific epidemiological cutoff values (ECV). To assess the effect of modified cutoff values on Candida glabrata resistance rates and agreement between testing methods, we tested the susceptibility of 598 clinical isolates to fluconazole, itraconazole, voriconazole, posaconazole, caspofungin, and amphotericin B using CLSI M27-A3 and E-test methods. The caspofungin MICs clustered above the ECV and below the CLSI cutoff (MIC50, 0.5 μg/mL). Applying the ECV reduced the proportion of itraconazole-nonsusceptible strains from 83% to 0.3% but minimally affected resistance rates of other drugs. Categorical agreement between broth microdilution and E-test was increased for itraconazole and reduced for voriconazole and caspofungin. The current caspofungin ECV may not reproducibly differentiate resistant and susceptible C. glabrata strains in hospitals with varying MIC distributions.