Use of Epidemiological Cutoff Values To Examine 9-Year Trends in Susceptibility of Aspergillus Species to the Triazoles

In the absence of clinical breakpoints, epidemiological cutoff values (ECVs) have been established to distinguish wild-type (WT) isolates of Aspergillus spp. from those that may harbor resistance mutations. Recently, the CLSI has developed ECVs for triazoles (itraconazole, posaconazole, and voriconazole) and common Aspergillus species. We applied the triazole ECVs to 1,789 Aspergillus isolates collected from 63 centers worldwide from 2001 to 2009 to determine the frequency of non-WT strains of each species. Temporal trends were evaluated for Aspergillus fumigatus and Aspergillus flavus over the 9-year period for each drug. The collection included 1,312 isolates of A. fumigatus, 235 of A. flavus, 162 of Aspergillus niger, 64 of Aspergillus terreus, and 15 of Aspergillus versicolor. Using the ECVs, the percentages of non-WT isolates for itraconazole, posaconazole, and voriconazole, respectively, were as follows: A. fumigatus (2.0%, 3.5%, and 1.4%), A. flavus (0.8%, 5.1%, and 1.7%), A. niger (17.3%, 3.7%, and 0.6%), A. terreus (0.0%, 1.6%, and 3.2%), and A. versicolor (6.3%, 0.0%, and 0.0%). Among 49 Aspergillus isolates for which itraconazole MICs were >2 μg/ml, the posaconazole and voriconazole MICs were greater than the ECVs for 14 and 12 isolates, respectively. The percentages of isolates for which MICs were greater than the ECVs ranged from 1.1 to 5.7% for posaconazole, 0.0 to 1.6% for voriconazole, and 0.7 to 4.0% for itraconazole. There was no consistent trend toward decreased susceptibility for any triazole and A. fumigatus or A. flavus over time. Decreased susceptibility among Aspergillus spp. was observed for each of the extended-spectrum triazoles and varied by species over the 9-year study period.