Q-BETA REPLICASE-AMPLIFIED ASSAY FOR DETECTION OF MYCOBACTERIUM-TUBERCULOSIS DIRECTLY FROM CLINICAL SPECIMENS

We report the results of a study conducted to evaluate the performance of manual Q-Beta replicase-amplified Mycobacterium tuberculosis compl ex assay compared with that of culture for detecting M. tuberculosis d irectly from digested sputum pellets, A total of 261 specimens submitt ed to three tuberculosis testing laboratories were analyzed. Culture a nd acid-fast bacillus smear results were provided by the tuberculosis testing laboratories. Of these 261 specimens, 34 (13% prevalence rate) were positive for M. tuberculosis by culture. The samples were digest ed and decontaminated by the testing laboratories by using their stand ard digestion and decontamination procedures. An aliquot of the digest ed and decontaminated pellet was sent to GENE-TRAK. The digested and d econtaminated pellet was neutralized by washing it with 0.067 M phosph ate buffer (pH 6.8), and the bacteria present in the washed pellet wer e heat inactivated at 100 degrees C for 15 min. The samples were combi ned with sample processing buffer containing GuSCN and were treated fo r 6 min in the GENE-TRAK Sample Processing Instrument to release the n ucleic acids. The released rRNA was analyzed ir a manual Q-Beta replic ase assay format which incorporates elements of sandwich hybridization , reversible target capture, and Q-Beta replicase signal amplification technologies. In comparison with culture, the overall assay sensitivi ty and specificity were 97.1 and 96.5%, respectively. The positive pre dictive value was 80.5%, and the negative predictive value was 99.5%. After analysis of discrepant results, the assay sensitivity and specif icity were 97.3 and 97.8%, respectively, and the prevalence rate was 1 4%. The positive predictive value and the negative predictive value we re 87.8 and 99.5%, respectively. The Q-Beta replicase assay is rapid, sensitive, semiquantitative, and specific for the direct detection of M. tuberculosis from clinical specimens.