Multicenter evaluation of a pathogenic Mycobacterium screening probe

The introduction of nucleic acid amplification assays into the clinical lab oratory has reduced the time needed to diagnose diseases caused by members of the Mycobacterium tuberculosis complex (MTBC). However, several mycobact erial species other than those of the MTBC are known to cause disease, espe cially in immunocompromised individuals. A screening assay has been develop ed for the detection of the major pathogenic mycobacterial species. The ass ay utilizes pan-genus primers to amplify mycobacterial DNA and a screening probe (KY493) that detects all major pathogenic mycobacteria. A multicenter European study was conducted to assess the performance of the screening pr obe in the clinical laboratory. The screening probe was evaluated against i ndividual probes specific for M. tuberculosis, M. avium, and M. intracellul are, a genus-specific probe with broader species coverage, and culture. The screening probe had a sensitivity equivalent to that of the species-specif ic probes; all specimens positive with any of the species-specific probes w ere also positive with the screening probes. Compared to culture, the sensi tivity of the screening probe was 89% (154 of 173) for all culture-positive specimens tested. This value was 89.6% for the genus-specific probe. The s creening probe was more specific than the genus-specific probe. Specificity was 93.9% (661 of 704) compared to culture results alone. The comparable s pecificity value for the genus-specific probe was 84.8%. When clinical data were taken into consideration, the sensitivity of the screening assay was similar to that of culture (81% versus 76.2%) but the positive predictive v alue of the test was lower (76.2% versus 100% for culture). However, the sc reening probe was more sensitive than smear and may be a useful tool in the rapid diagnosis of mycobacterial disease.