Evaluation of Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test and Roche PCR-Microwell Plate Hybridization Method (AMPLICOR MYCOBACTERIUM) for direct detection of mycobacteria

We evaluated the clinical utility of an rRNA amplification-based Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test (AMTD) system and a PCR-based Roche AMPLICOR MYCOBACTERIUM? system for direct detection of Mycobacterium tuberculosis, M. avium, and M. intracellulare. Of the 422 sputum samples from 170 patients, 137 (121 of M. tuberculosis, 14 of M. avium-M. intracellulare complex [MAC], 2 of mycobacterium other than M. tuberculosis or MAC) were culture positive with the Septi-Chek AFB system. One sample of a contaminated culture result was excluded for further analyses. The AMTD system detected all of the 121 samples which grew M. tuberculosis (sensitivity, 100%). Of the 284 culture negative samples, 28 were positive by this system (specificity, 90.1%). After resolution of the discrepant samples, based on a positive history for culture of the patient, the specificity of this system increased to 99.3%. On the other. hand, the AMPLICOR system gave a positive result for 132 out of the 135 culture positive samples for M. tuberculosis or MAC (sensitivity, 97.8%). Of the 284 culture-negative samples, 37 were positive by this system (specificity, 87.0%). The specificity for this system after resolution of the discrepant samples increased to 98.9%. The agreement between the results from the AMTD system and the AMPLICOR system was 98.7%. Both of the systems are highly sensitive and specific for detecting M. tuberculosis and/or MAC directly from sputum samples within hours, and they should be recommended for routine use in the clinical microbiology laboratory.