Comparison of results of voriconazole disk diffusion testing for Candida species with results from a central reference laboratory in the ARTEMIS global antifungal surveillance program

Abstract

The accuracy of antifungal susceptibility testing is important for reliable resistance surveillance and for the clinical management of patients with serious infections. Our primary objective was to compare the results of voriconazole disk diffusion testing of Candida spp. performed by centers participating in the ARTEMIS program with disk diffusion and MIC results obtained by the central reference laboratory. A total of 2,934 isolates of Candida spp. were tested by CLSI disk diffusion and reference broth microdilution methods in the central reference laboratory. These results were compared to the results of disk diffusion testing performed in the 54 participating centers. All tests were performed and interpreted following CLSI recommendations, as follows: susceptible (S), MIC of <or=1 microg/ml (>or=17 mm); susceptible dose dependent (SDD), MIC of 2 microg/ml (14 to 16 mm); and resistant (R), MIC of >or=4 microg/ml (<or=13 mm). The overall categorical agreement between participant disk diffusion test results and reference laboratory MIC results was 94.1%, with 0.1% very major errors (VME) and 3.4% major errors (ME). The categorical agreement between disk diffusion test results obtained in the reference laboratory and the MIC test results was 99.0%. Likewise, good agreement was observed between participant disk diffusion test results and reference laboratory disk diffusion test results, with an agreement of 93.8%, 0.2% VME, and 3.4% ME. The disk diffusion test was reliable for detecting those isolates of Candida spp. that were characterized as resistant (MIC of >or=4 microg/ml) by MIC testing. External quality assurance data obtained by surveillance programs such as the ARTEMIS Global Antifungal Surveillance Program ensure the generation of useful surveillance data and result in the continued improvement of antifungal susceptibility testing practices.

FIG. 1.

Zones of inhibition around 1-μg/ml voriconazole disks tested in ARTEMIS participating laboratories plotted against the MICs determined at 48 h by using the reference BMD method for 2,934 isolates of Candida spp. The numbers represent the number of results (isolates) for each data point, and the dotted line is the regression line.

FIG. 2.

Zones of inhibition around 1-μg/ml voriconazole disks tested in the ARTEMIS central reference laboratory plotted against the MICs determined at 48 h by using the reference BMD method for 2,934 isolates of Candida spp. The numbers represent the number of results (isolates) for each data point, and the dotted line is the regression line.