RAPID DETECTION OF MYCOBACTERIUM-TUBERCULOSIS IN RESPIRATORY SPECIMENS, BLOOD AND OTHER NON-RESPIRATORY SPECIMENS BY AMPLIFICATION OF RIBOSOMAL-RNA

SETTING: Diagnostic methods employing gene technology based on amplifi cation of DNA or RNA are expected to improve the speed, sensitivity, a nd specificity of Mycobacterium tuberculosis detection. The Amplified Mycobacterium Tuberculosis Direct Test (AMTDT) enables the amplificati on and detection of M. tuberculosis rRNA directly from respiratory spe cimens. OBJECTIVE: To evaluate the performance of the AMTDT in direct detection of M. tuberculosis in respiratory specimens, blood and other clinical samples, and to compare this method with conventional cultur e and staining techniques. DESIGN: A total of 554 samples from 450 pat ients were examined in this study. All clinical specimens (with the ex ception of bone marrow aspirates and blood samples) were digested and decontaminated with sodium dodecyl (lauryl) sulfate (SDS)-NaOH. Bone m arrow aspirates and blood samples were treated with 10% SDS. Ail proce ssed samples were stained by auramine-rhodamine fluorochrome and inocu lated onto Lowenstein-Jensen and Coletsos solid media, and into BACTEC -12B medium. In addition, the blood samples were inoculated into BACTE C 13A medium. The AMTDT was performed according to manufacturer's inst ructions. In those cases where discrepant results were obtained for AM TDT and cultures, patients' clinical data and other microbiological re sults were evaluated. RESULTS: The sensitivity, specificity, and posit ive and negative predictive values for AMTDT were 87.5, 100, 100, and 96.7%, respectively, in respiratory specimens and 86.8, 100, 100, and 92.8%, respectively, in nonrespiratory specimens. The differences in s ensitivity of these two groups of specimens were not highly statistica lly significant (P > 0.005). CONCLUSION: The sensitivity and specifici ty of the AMTDT were satisfactory for detection of M. tuberculosis in all types of clinical samples. Some minor changes in assay format and laboratory protocols may increase the sensitivity of the AMTDT without adversely affecting its specificity.