Evaluation of the Gen-Probe amplified Mycobacterium tuberculosis direct test for the routine diagnosis of pulmonary tuberculosis

A total of 624 respiratory specimens from 543 patients (418 Belgian, 110 Rwandan, and 15 Colombian patients) were tested for the presence of Mycobacterium tuberculosis by the Mycobacterium Tuberculosis Direct Test (MTDT, Gen-Probe). Compared to culture, the MTDT on 497 samples of sputum or broncho-alveolar lavage from Belgium had a sensitivity, specificity and positive and negative predictive value of 86.4%, 96.0%, 50.0% and 99.3% respectively. The pooled results for Rwanda (112 specimens) and Colombia (15 specimens) were 97.8%, 65.7%, 88.2%, 92% respectively. After resolution of discrepant results by taking into account the clinical data, the results for the Belgian patients were 86.9%, 96.2%, 52.6%, 99.3% respectively, and for the Rwandan-Colombian patients 98.1%, 100%, 100% and 92% respectively. Results could be improved by testing more than one specimen from each patient and the inclusion of an internal control to detect inhibitors of the reaction. Culture remains necessary for drug susceptibility tests and the isolation and identification of non-tuberculous mycobacteria.