Comparison of Results of Voriconazole Disk Diffusion Testing for Candida Species with Results from a Central Reference Laboratory in the ART
http://www.100md.com
微生物临床杂志 2005年第10期
Departments of Pathology Epidemiology
Medicine, Roy J. and Lucille A. Carver College of Medicine and College of Public Health, University of Iowa, Iowa City, Iowa 52242
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 1 μg/ml (17 mm); susceptible dose dependent (SDD), MIC of 2 μg/ml (14 to 16 mm); and resistant (R), MIC of 4 μg/ml (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 4 μg/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.
INTRODUCTION
One of the important by-products of the standardization of antifungal susceptibility testing methods has been the ability to conduct active surveillance of resistance to antifungal agents (12, 17, 18, 21, 23, 24). Meaningful large-scale studies of antifungal susceptibility and resistance conducted over time would not be possible without a standardized microdilution method for performing in vitro studies (6, 22-24). Many such studies have now been published and include studies of isolates from patients in intensive care units (4, 16, 25) and of nosocomial bloodstream infections (BSI) in the United States and other countries worldwide (1, 5-8, 14, 15, 21, 23, 24, 30, 32, 33). Furthermore, studies of resistance trends to commonly used antifungal agents such as fluconazole (1, 5-8, 10, 14, 21, 23, 24, 35) and comparative analyses of newly licensed and established antifungal agents (9, 10, 18, 21, 25-31) have provided large amounts of useful data and have been greatly facilitated by a standardized microdilution method (19).
In addition to broth microdilution (BMD) MIC determination methods, disk diffusion testing of fluconazole and voriconazole activities against Candida spp. has been developed and standardized in order to provide a simple inexpensive method for monitoring susceptibilities to these agents in a variety of laboratory settings (3, 12, 15, 17, 20, 30, 31). The Clinical and Laboratory Standards Institute (CLSI; formerly the NCCLS) M44-A agar disk diffusion method (20) has been used for more than 4 years to monitor the susceptibility of Candida spp. to fluconazole and voriconazole as part of the ARTEMIS Global Antifungal Surveillance Program (12, 17, 34, 36). In the ARTEMIS program, fluconazole and voriconazole disk diffusion testing is performed in accordance with CLSI M44-A in more than 120 laboratories in 39 countries (ARTEMIS DISK Surveillance Study), and the data are used to follow trends in fluconazole and voriconazole susceptibility patterns worldwide (12, 17, 36). In addition to on-site testing, BSI isolates of Candida spp. collected by ARTEMIS participants are sent to a central reference laboratory at the University of Iowa for confirmatory testing using CLSI disk diffusion and BMD methods (30, 31, 34). Data generated from this program have been useful for documenting the sustained activities of both fluconazole and voriconazole against clinical isolates of Candida (12, 17, 30, 34, 36).
Although the ARTEMIS DISK Surveillance Study (12, 17, 36) generates massive amounts of data, it is recognized that despite the use of a standard protocol, any surveillance system based on susceptibility tests performed by the participating laboratories must include some measure of quality assurance, beyond simple quality control testing, in order to provide an independent assessment of laboratory performance and a validation of results generated from the various laboratories (13, 34, 37). As such, we have recently documented a good agreement between ARTEMIS participant disk diffusion results for fluconazole and reference laboratory disk diffusion and BMD MIC test results (34). In the present study, we assess the accuracy of the ARTEMIS participant voriconazole disk diffusion results by comparing them to those obtained for the same isolates tested in the central reference laboratory by disk diffusion and BMD methods recommended by the CLSI.
MATERIALS AND METHODS
Study design. The ARTEMIS program was established to monitor the species and antifungal susceptibility patterns of Candida spp. isolated from clinically significant sites of infection (e.g., blood and normally sterile sites [NSSI]) via a broad network of sentinel laboratories in North America, Latin America, Europe, Africa, and Asia. Candida spp. causing invasive disease (in blood and NSSI) and the accompanying voriconazole disk zone diameters were reported from 54 different medical centers in 2001 and 2002.
Each participant medical center contributed results (organism identification and voriconazole disk zone diameters) for consecutive blood and NSSI culture isolates (one isolate per patient) of Candida spp. judged to be clinically significant by local criteria and detected in each calendar month during the study. All isolates were saved on agar slants and were sent to the University of Iowa College of Medicine (Iowa City) for storage and further characterization by reference identification methods and susceptibility testing (11, 19, 20). In the central reference laboratory, isolates were tested by both CLSI disk diffusion (20) and BMD (19) methods.
Organism identification. All Candida sp. isolates were identified at participating institutions by the routine method used in each laboratory. Upon receipt at the University of Iowa, the isolates were subcultured onto potato dextrose agar (Remel, Lenexa, Kans.) and CHROMagar Candida medium (Hardy Laboratories, Santa Maria, Calif.) to ensure their viability and purity. Confirmation of the species identification was performed with Vitek and API products (bioMerieux, St. Louis, Mo.), as recommended by the manufacturer, or by conventional methods as required (11). Isolates were stored as suspensions in water or on agar slants at ambient temperature until needed.
Susceptibility testing. Disk diffusion testing of voriconazole was performed in both participant laboratories and the central reference laboratory according to the methods described in CLSI document M44-A (20). MIC testing was performed by the CLSI BMD reference method M27-A2 (19). Standard voriconazole reference powder was obtained from Pfizer Pharmaceuticals (Groton, Conn.), and 1-μg voriconazole disks were obtained from Becton Dickinson (Sparks, Md.).
Disk diffusion testing of voriconazole was performed as described by Hazen et al. (12) and in CLSI document M44-A (20). Agar plates (150-mm diameter) containing Mueller-Hinton agar supplemented with 2% glucose and 0.5 μg of methylene blue per ml at a depth of 4.0 mm were used. The agar surface was inoculated by using a swab dipped in a cell suspension adjusted to the turbidity of a 0.5 McFarland standard. The plates were incubated in air at 35 to 37°C and read at 18 to 24 h. Zone diameter end points were read at 80% growth inhibition by using the BIOMIC image analysis plate reader system (version 5.9; Giles Scientific, Santa Barbara, Calif.) (10, 30).
MIC interpretive criteria for voriconazole were those approved by CLSI (Minutes of CLSI Antifungal Subcommittee Meeting, 2005), as follows: susceptible, MIC of 1 μg/ml; susceptible dose dependent, MIC of 2 μg/ml; and resistant, MIC of 4 μg/ml. The interpretive criteria for the voriconazole disk diffusion test were those used by CLSI (Minutes of CLSI Antifungal Subcommittee Meeting, 2005), as follows: susceptible, zone diameter of 17 mm; susceptible dose dependent, zone diameter of 14 to 16 mm; and resistant, zone diameter of 13 mm.
Quality control. Quality control was performed in accordance with CLSI documents M27-A2 (19) and M44-A (20) by using Candida krusei ATCC 6258 and C. parapsilosis ATCC 22019 (2, 19, 20).
Analysis of results. The diameters of the zones of inhibition (in millimeters) surrounding the voriconazole disks after 24 h of incubation obtained in the participant laboratories and in the reference laboratory were plotted against their respective BMD MICs read at 48 h (Fig. 1 and 2) (3, 30, 34). Similarly, the diameters of the zones of inhibition surrounding the voriconazole disks after 24 h of incubation obtained in the participant laboratories were plotted against their respective zones obtained in the reference laboratory at 24 h. The interpretive breakpoints recently approved by CLSI (Minutes of the CLSI Antifungal Subcommittee Meeting, 2005) were used to determine the categorical agreement between disk diffusion and BMD MIC results and between participant and reference disk diffusion results. Major errors (ME) were classified as resistant by disk diffusion (participant or central laboratory) and susceptible by BMD or resistant by the participant disk diffusion test and susceptible by the central laboratory disk diffusion test. Very major errors (VME) were classified as susceptible by the participant or central laboratory disk diffusion test and resistant by BMD or susceptible by the participant disk diffusion test and resistant by the central laboratory disk diffusion test. Minor errors (M) occurred when the result of one of the tests was susceptible or resistant and that of the other test was susceptible dose dependent.
RESULTS AND DISCUSSION
During the 2001-2002 study period, a total of 2,934 isolates of Candida spp. from blood and other NSSI and their accompanying voriconazole disk diffusion zone diameters were submitted from 54 participating centers in North America (8 centers), Latin America (12 centers), Europe (20 centers), and the Asia-Pacific region (14 centers). The frequencies of infections due to the various species of Candida identified in the central reference laboratory are presented in Table 1 and represent a total of 14 different species.
In vitro susceptibility testing performed in both participant laboratories (disk diffusion test) and the reference laboratory (disk diffusion and MIC tests) indicated that resistance to voriconazole was very uncommon among isolates of Candida from blood and NSSI (Table 2). As seen in our previous study with fluconazole (34), more isolates of all species appeared resistant to voriconazole by disk diffusion testing in both participant and reference laboratories, with the greatest resistance observed with disk diffusion testing performed in participant laboratories (Table 2). Overall, the level of categorical agreement between the disk diffusion test results and the reference MIC results was excellent in both participant (94.1%) and reference (99.0%) laboratories (Table 2), exceeding the levels reported previously for fluconazole (87.4% and 92.8%, respectively) (34). Although resistant isolates were uncommon, it is important that there were very few VME, indicating that the disk diffusion test was reliable for detecting isolates resistant to voriconazole by MIC testing (MIC, 4 μg/ml). The level of agreement between disk diffusion and MIC results was highest for C. albicans and lowest for C. glabrata and C. tropicalis. The decreased level of agreement with C. glabrata and C. tropicalis was largely due to false-resistant disk diffusion results (ME) reported by the participant laboratories.
A similar level of agreement was seen when disk diffusion results obtained in the participant laboratories were compared with those obtained in the reference laboratory (Table 3). The overall categorical agreement was excellent, at 93.8%, and the number of VME, ME, and M was very low. As with the comparison to BMD testing, agreement was highest for C. albicans and lowest for C. glabrata and C. tropicalis, with most of the errors in the ME category.
Over 99% of the quality control tests at participating ARTEMIS centers were in control.
Taken together with our previous study of fluconazole disk testing (34), this study constitutes the largest available body of data validating the performance of disk diffusion testing in surveillance program participant laboratories. We demonstrate that in addition to fluconazole testing, voriconazole disk diffusion testing using the CLSI M44-A method can be performed with a high degree of accuracy in more than 50 laboratories worldwide. The participant results were validated not only by voriconazole disk diffusion testing performed in the central reference laboratory but also by reference BMD MIC testing. The data reported herein also represent the first application of the newly approved disk zone and MIC interpretive criteria for voriconazole and document the very low level of resistance to this agent among a large group of clinically significant isolates of Candida.
In summary, we have shown that voriconazole disk diffusion testing performed in accordance with the CLSI M44-A method can be performed with a high degree of accuracy in a wide range of laboratory settings throughout the world. The test was reliable in identifying those strains of Candida characterized as resistant by reference BMD MIC testing. As seen with fluconazole, false-resistant results may be an issue with C. glabrata and other non-C. albicans species. Further assessment of such isolates by BMD should be performed if clinically indicated. This external validation of antifungal susceptibility testing results is an important component of the ARTEMIS Global Antifungal Surveillance Program and ensures the generation of useful antifungal surveillance data and the continued improvement of antifungal susceptibility testing practices.
ACKNOWLEDGMENTS
This study was supported in part by research and educational grants from Pfizer Inc., Pfizer Global Pharmaceuticals, New York, N.Y.
We thank Linda Elliott for secretarial assistance with the preparation of the manuscript. We appreciate the participation of all ARTEMIS site participants. A list of ARTEMIS participants can be found at the following website: http://www.medicine.uiowa.edu/pathology /path_folder/research/acknowledgements/artemis_participants.pdf.
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Medicine, Roy J. and Lucille A. Carver College of Medicine and College of Public Health, University of Iowa, Iowa City, Iowa 52242
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 1 μg/ml (17 mm); susceptible dose dependent (SDD), MIC of 2 μg/ml (14 to 16 mm); and resistant (R), MIC of 4 μg/ml (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 4 μg/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.
INTRODUCTION
One of the important by-products of the standardization of antifungal susceptibility testing methods has been the ability to conduct active surveillance of resistance to antifungal agents (12, 17, 18, 21, 23, 24). Meaningful large-scale studies of antifungal susceptibility and resistance conducted over time would not be possible without a standardized microdilution method for performing in vitro studies (6, 22-24). Many such studies have now been published and include studies of isolates from patients in intensive care units (4, 16, 25) and of nosocomial bloodstream infections (BSI) in the United States and other countries worldwide (1, 5-8, 14, 15, 21, 23, 24, 30, 32, 33). Furthermore, studies of resistance trends to commonly used antifungal agents such as fluconazole (1, 5-8, 10, 14, 21, 23, 24, 35) and comparative analyses of newly licensed and established antifungal agents (9, 10, 18, 21, 25-31) have provided large amounts of useful data and have been greatly facilitated by a standardized microdilution method (19).
In addition to broth microdilution (BMD) MIC determination methods, disk diffusion testing of fluconazole and voriconazole activities against Candida spp. has been developed and standardized in order to provide a simple inexpensive method for monitoring susceptibilities to these agents in a variety of laboratory settings (3, 12, 15, 17, 20, 30, 31). The Clinical and Laboratory Standards Institute (CLSI; formerly the NCCLS) M44-A agar disk diffusion method (20) has been used for more than 4 years to monitor the susceptibility of Candida spp. to fluconazole and voriconazole as part of the ARTEMIS Global Antifungal Surveillance Program (12, 17, 34, 36). In the ARTEMIS program, fluconazole and voriconazole disk diffusion testing is performed in accordance with CLSI M44-A in more than 120 laboratories in 39 countries (ARTEMIS DISK Surveillance Study), and the data are used to follow trends in fluconazole and voriconazole susceptibility patterns worldwide (12, 17, 36). In addition to on-site testing, BSI isolates of Candida spp. collected by ARTEMIS participants are sent to a central reference laboratory at the University of Iowa for confirmatory testing using CLSI disk diffusion and BMD methods (30, 31, 34). Data generated from this program have been useful for documenting the sustained activities of both fluconazole and voriconazole against clinical isolates of Candida (12, 17, 30, 34, 36).
Although the ARTEMIS DISK Surveillance Study (12, 17, 36) generates massive amounts of data, it is recognized that despite the use of a standard protocol, any surveillance system based on susceptibility tests performed by the participating laboratories must include some measure of quality assurance, beyond simple quality control testing, in order to provide an independent assessment of laboratory performance and a validation of results generated from the various laboratories (13, 34, 37). As such, we have recently documented a good agreement between ARTEMIS participant disk diffusion results for fluconazole and reference laboratory disk diffusion and BMD MIC test results (34). In the present study, we assess the accuracy of the ARTEMIS participant voriconazole disk diffusion results by comparing them to those obtained for the same isolates tested in the central reference laboratory by disk diffusion and BMD methods recommended by the CLSI.
MATERIALS AND METHODS
Study design. The ARTEMIS program was established to monitor the species and antifungal susceptibility patterns of Candida spp. isolated from clinically significant sites of infection (e.g., blood and normally sterile sites [NSSI]) via a broad network of sentinel laboratories in North America, Latin America, Europe, Africa, and Asia. Candida spp. causing invasive disease (in blood and NSSI) and the accompanying voriconazole disk zone diameters were reported from 54 different medical centers in 2001 and 2002.
Each participant medical center contributed results (organism identification and voriconazole disk zone diameters) for consecutive blood and NSSI culture isolates (one isolate per patient) of Candida spp. judged to be clinically significant by local criteria and detected in each calendar month during the study. All isolates were saved on agar slants and were sent to the University of Iowa College of Medicine (Iowa City) for storage and further characterization by reference identification methods and susceptibility testing (11, 19, 20). In the central reference laboratory, isolates were tested by both CLSI disk diffusion (20) and BMD (19) methods.
Organism identification. All Candida sp. isolates were identified at participating institutions by the routine method used in each laboratory. Upon receipt at the University of Iowa, the isolates were subcultured onto potato dextrose agar (Remel, Lenexa, Kans.) and CHROMagar Candida medium (Hardy Laboratories, Santa Maria, Calif.) to ensure their viability and purity. Confirmation of the species identification was performed with Vitek and API products (bioMerieux, St. Louis, Mo.), as recommended by the manufacturer, or by conventional methods as required (11). Isolates were stored as suspensions in water or on agar slants at ambient temperature until needed.
Susceptibility testing. Disk diffusion testing of voriconazole was performed in both participant laboratories and the central reference laboratory according to the methods described in CLSI document M44-A (20). MIC testing was performed by the CLSI BMD reference method M27-A2 (19). Standard voriconazole reference powder was obtained from Pfizer Pharmaceuticals (Groton, Conn.), and 1-μg voriconazole disks were obtained from Becton Dickinson (Sparks, Md.).
Disk diffusion testing of voriconazole was performed as described by Hazen et al. (12) and in CLSI document M44-A (20). Agar plates (150-mm diameter) containing Mueller-Hinton agar supplemented with 2% glucose and 0.5 μg of methylene blue per ml at a depth of 4.0 mm were used. The agar surface was inoculated by using a swab dipped in a cell suspension adjusted to the turbidity of a 0.5 McFarland standard. The plates were incubated in air at 35 to 37°C and read at 18 to 24 h. Zone diameter end points were read at 80% growth inhibition by using the BIOMIC image analysis plate reader system (version 5.9; Giles Scientific, Santa Barbara, Calif.) (10, 30).
MIC interpretive criteria for voriconazole were those approved by CLSI (Minutes of CLSI Antifungal Subcommittee Meeting, 2005), as follows: susceptible, MIC of 1 μg/ml; susceptible dose dependent, MIC of 2 μg/ml; and resistant, MIC of 4 μg/ml. The interpretive criteria for the voriconazole disk diffusion test were those used by CLSI (Minutes of CLSI Antifungal Subcommittee Meeting, 2005), as follows: susceptible, zone diameter of 17 mm; susceptible dose dependent, zone diameter of 14 to 16 mm; and resistant, zone diameter of 13 mm.
Quality control. Quality control was performed in accordance with CLSI documents M27-A2 (19) and M44-A (20) by using Candida krusei ATCC 6258 and C. parapsilosis ATCC 22019 (2, 19, 20).
Analysis of results. The diameters of the zones of inhibition (in millimeters) surrounding the voriconazole disks after 24 h of incubation obtained in the participant laboratories and in the reference laboratory were plotted against their respective BMD MICs read at 48 h (Fig. 1 and 2) (3, 30, 34). Similarly, the diameters of the zones of inhibition surrounding the voriconazole disks after 24 h of incubation obtained in the participant laboratories were plotted against their respective zones obtained in the reference laboratory at 24 h. The interpretive breakpoints recently approved by CLSI (Minutes of the CLSI Antifungal Subcommittee Meeting, 2005) were used to determine the categorical agreement between disk diffusion and BMD MIC results and between participant and reference disk diffusion results. Major errors (ME) were classified as resistant by disk diffusion (participant or central laboratory) and susceptible by BMD or resistant by the participant disk diffusion test and susceptible by the central laboratory disk diffusion test. Very major errors (VME) were classified as susceptible by the participant or central laboratory disk diffusion test and resistant by BMD or susceptible by the participant disk diffusion test and resistant by the central laboratory disk diffusion test. Minor errors (M) occurred when the result of one of the tests was susceptible or resistant and that of the other test was susceptible dose dependent.
RESULTS AND DISCUSSION
During the 2001-2002 study period, a total of 2,934 isolates of Candida spp. from blood and other NSSI and their accompanying voriconazole disk diffusion zone diameters were submitted from 54 participating centers in North America (8 centers), Latin America (12 centers), Europe (20 centers), and the Asia-Pacific region (14 centers). The frequencies of infections due to the various species of Candida identified in the central reference laboratory are presented in Table 1 and represent a total of 14 different species.
In vitro susceptibility testing performed in both participant laboratories (disk diffusion test) and the reference laboratory (disk diffusion and MIC tests) indicated that resistance to voriconazole was very uncommon among isolates of Candida from blood and NSSI (Table 2). As seen in our previous study with fluconazole (34), more isolates of all species appeared resistant to voriconazole by disk diffusion testing in both participant and reference laboratories, with the greatest resistance observed with disk diffusion testing performed in participant laboratories (Table 2). Overall, the level of categorical agreement between the disk diffusion test results and the reference MIC results was excellent in both participant (94.1%) and reference (99.0%) laboratories (Table 2), exceeding the levels reported previously for fluconazole (87.4% and 92.8%, respectively) (34). Although resistant isolates were uncommon, it is important that there were very few VME, indicating that the disk diffusion test was reliable for detecting isolates resistant to voriconazole by MIC testing (MIC, 4 μg/ml). The level of agreement between disk diffusion and MIC results was highest for C. albicans and lowest for C. glabrata and C. tropicalis. The decreased level of agreement with C. glabrata and C. tropicalis was largely due to false-resistant disk diffusion results (ME) reported by the participant laboratories.
A similar level of agreement was seen when disk diffusion results obtained in the participant laboratories were compared with those obtained in the reference laboratory (Table 3). The overall categorical agreement was excellent, at 93.8%, and the number of VME, ME, and M was very low. As with the comparison to BMD testing, agreement was highest for C. albicans and lowest for C. glabrata and C. tropicalis, with most of the errors in the ME category.
Over 99% of the quality control tests at participating ARTEMIS centers were in control.
Taken together with our previous study of fluconazole disk testing (34), this study constitutes the largest available body of data validating the performance of disk diffusion testing in surveillance program participant laboratories. We demonstrate that in addition to fluconazole testing, voriconazole disk diffusion testing using the CLSI M44-A method can be performed with a high degree of accuracy in more than 50 laboratories worldwide. The participant results were validated not only by voriconazole disk diffusion testing performed in the central reference laboratory but also by reference BMD MIC testing. The data reported herein also represent the first application of the newly approved disk zone and MIC interpretive criteria for voriconazole and document the very low level of resistance to this agent among a large group of clinically significant isolates of Candida.
In summary, we have shown that voriconazole disk diffusion testing performed in accordance with the CLSI M44-A method can be performed with a high degree of accuracy in a wide range of laboratory settings throughout the world. The test was reliable in identifying those strains of Candida characterized as resistant by reference BMD MIC testing. As seen with fluconazole, false-resistant results may be an issue with C. glabrata and other non-C. albicans species. Further assessment of such isolates by BMD should be performed if clinically indicated. This external validation of antifungal susceptibility testing results is an important component of the ARTEMIS Global Antifungal Surveillance Program and ensures the generation of useful antifungal surveillance data and the continued improvement of antifungal susceptibility testing practices.
ACKNOWLEDGMENTS
This study was supported in part by research and educational grants from Pfizer Inc., Pfizer Global Pharmaceuticals, New York, N.Y.
We thank Linda Elliott for secretarial assistance with the preparation of the manuscript. We appreciate the participation of all ARTEMIS site participants. A list of ARTEMIS participants can be found at the following website: http://www.medicine.uiowa.edu/pathology /path_folder/research/acknowledgements/artemis_participants.pdf.
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