Evaluation of the BDProbeTec ET system as screening tool in the direct detection of mycobacterium tuberculosis complex in respiratory specimens

We evaluated the BDProbeTec ET System (Becton Dickinson) for the routine detection of Mycobacterium tuberculosis complex (MTC) in respiratory specimens and pleural fluids, comparing with microscopy (Ziehl Neelsen stain, ZN) and culture in liquid (BACTEC MGIT 960, MGIT) and solid (Löwenstein Jensen, LJ) media. Five hundred and two specimens, collected from 266 patients, of which 257 with suspected tuberculosis and 9 receiving anti-tuberculosis treatment, were investigated. Thirty-nine specimens were positive by any method, including false positives. Mycobacteria were isolated from 33 specimens (32 Mycobacterium tuberculosis and 1 Mycobacterium chelonae). Thirty-six specimens were BDProbeTec ET positive, 33 specimens were MGIT positive, 27 were LJ positive and 22 were ZN positive. With BDProbeTec ET, 2 specimens were false negative (culture positive), and 2 specimens from non-treated patients were false positive (culture negative). The overall sensitivity, specificity, and positive and negative predictive values for BDProbeTec ET compared to culture were 93.7, 98.7, 83.3, and 99.5%, respectively, while with smear-positive and smear-negative specimens the sensitivities were 100% and 81.5% respectively. In five treated patients the disappearance of MTC could be monitored using BDProbeTec ET in parallel with culture. The overall inhibition rate was 0.2%. BDProbeTec ET can be very useful for rapid detection of MTC, especially in smear-negative respiratory specimens.