[Reproducibility of MTD system for detection of Mycobacterium tuberculosis: a cooperative study among six laboratories].

The Gen-Probe Amplified Mycobacterium Tuberculosis Direct Test (MTD) is a rapid test for the detection of Mycobacterium tuberculosis, utilizing the rRNA amplification method. For assessing the reliability and reproducibility of the method, a co-operative blind study was conducted among 6 laboratories. Materials for test were sputum and water samples containing known numbers of Mycobacterium bovis BCG or Mycobacterium avium, and samples without bacteria. From three of 6 laboratories, false-positive results were reported for bacteria negative samples, however, the ratio was below 10%; 8.3% (3/36 samples), 5.6% (2/36), and 2.8% (1/36), respectively. It indicates the indispensability of negative controls for sample pretreatment and RNA extraction stages in the routine MTD test. In every laboratory, all the samples with 10(2) BCG in water and 10(4) BCG in sputum were found to be MTD positive. For the sputum samples with 10(2) BCG, positive results with the ratio above 80% were reported from 4 laboratories. These results indicate that the MTD test based on rRNA amplification method is quite useful for the rapid diagnosis of M. tuberculosis infection.