College of American Pathologists Mycobacteriology E Proficiency Testing Survey. Summary of participant performance, 1979-1992.

The College of American Pathologists first offered a program of proficiency testing in mycobacteriology in 1969 to laboratories that offered any extent of diagnostic service. This program was intended to provide a mechanism for evaluation of methods of staining, culture, identification, and susceptibility testing. From 1979 to 1992, the period covered by this review, participation in the Mycobacteriology E Survey increased almost sixfold. On graded smears to be stained for detection of acid-fast bacilli, more than 85% of Extent 4 and Extent 3 laboratories and more than 80% of Extent 2 laboratories responded correctly to all specimens except one. Performance on specimens that contained Mycobacterium tuberculosis was similar for Extent 4 and Extent 3 laboratories. For all specimens containing M tuberculosis, a mean of more than 90% of Extent 4 and Extent 3 laboratories provided a correct identification each year except 1979, when a mean of 83% of Extent 3 laboratories responded correctly. Only Extent 4 laboratories were required to identify isolates other than M tuberculosis to the species level. For specimens that contained nontuberculous mycobacteria, the means of the yearly averages of correct responses for Extent 4 laboratories were 90% or greater for M kansasii, M marinum, M avium complex, and M fortuitum-chelonae complex and less than 85% for M bovis, M simiae, M scrofulaceum, M szulgai, M flavescens, M xenopi, M terrae complex, and M gastri. In general, on these same specimens, a slightly higher percentage of Extent 3 laboratories (which were required to identify only M tuberculosis to the species or complex level) gave correct or acceptable responses, and the performance of Extent 2 laboratories (which were only required to report whether or not a mycobacterium was present) was the best of all extents. The data suggest that laboratory performance improved somewhat after initial experience with uncommonly encountered organisms. For the most part, however, performance with a given species changed minimally from year to year.