Evaluations of Antimicrobial Susceptibility Test Proficiency by the College of American Pathologists Survey Program: A Clarification of Quality Control Recommendations

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Abstract
The College of American Pathologists (CAP) Interlaboratory Survey Program in microbiology was reviewed for quality control practices of the Special Bacteriology participants (907 laboratories) using the disk agar diffusion antimicrobial susceptibility test method. Data from a questionnaire was compared to performance results on two well recognized quality control strains, e.g., Pseudomonas aeruginosa ATCC 27853 and Streptococcus faecalis ATCC 29212. The results show no significant difference in survey performance between those participants using daily controls (97.78 and 96.99% acceptable results) and those using weekly controls (97.33 and 96.67% acceptable results). Similarly, the number of tests done per work day had little influence on the reported mean zone diameter and subscriber results were comparable to published means from the reference literature. Recommendations are made to use weekly quality control after test proficiency has been repeatedly demonstrated by daily or batch control results. More frequent testing would be required if any reagent lot were replaced or altered. Comparable data on quality control intervals of >7 days was not evaluated due to small numbers of test results.