EVALUATION OF A COMMERCIAL RIBOSOMAL-RNA AMPLIFICATION ASSAY FOR DIRECT-DETECTION OF MYCOBACTERIUM-TUBERCULOSIS IN PROCESSED SPUTUM

A commercial assay (Amplified Mycobacterium tuberculosis Direct Test, Gen Probe) which combines transcription-mediated amplification of targ et rRNA with amplicon detection by a chemiluminescent DNA probe for th e rapid detection of Mycobacterium tuberculosis in sputum was evaluate d. The test was applied to consecutively collected, NALC/NaOH processe d sputum sediments from two laboratories (H and L), each serving a dif ferent population of patients with pulmonary tuberculosis. Results wer e compared to those of fluorochrome staining and culture. A total of 7 60 specimens obtained from 246 patients were used for the study. The t est was positive in 141 of 144 (98 %) specimens that were fluorochrome -positive and culture-positive for Mycobacterium tuberculosis. Fifteen of 31 specimens that were fluorochrome-negative, culture-positive wer e also assay-positive. A total of 312 specimens (100 patients) from la boratory H (prevalence = 10 %) and 448 specimens (146 patients) from l aboratory L (prevalence = 34 %) were analyzed. Compared to culture, te st sensitivity, specificity, positive predictive and negative predicti ve values were 65 %, 99 %, 94 % and 97 %, respectively, for laboratory H and 93 %, 99 %, 99 % and 97 %, respectively, for laboratory L. If t he results were analyzed on the basis of at least one concordant resul t between the amplification assay and culture in three sputum samples per patient, then the sensitivity, specificity, positive and negative predictive values for identifying infected patients was 70 %, 99 %, 87 % and 97 %, respectively, for laboratory H, and 100 %, 98 %, 96 % and 100 %,respectively, for laboratory L.