Performance Assessment of Two Commercial Amplification Assays for Direct Detection ofMycobacterium tuberculosisComplex from Respiratory and Extrapulmonary Specimens

Abstract

The new BDProbeTec ET Mycobacterium tuberculosis Complex Direct Detection Assay (DTB) was compared with the enhanced M. tuberculosis Amplified Direct Test (AMTDII). The system is an automated walkaway system characterized by simultaneous DNA amplification (strand displacement amplification) and real-time fluorometric detection. It also contains an internal amplification control (IAC) designed to identify inhibition from the processed samples. The AMTDII assay amplifies rRNA by transcription-mediated amplification; it uses hybridization with a chemoluminescent probe as a detection system and is entirely manual. A total of 515 N-acetyl-L-cysteine-sodium hydroxide-decontaminated respiratory (n ‫؍‬ 331) and extrapulmonary (n ‫؍‬ 184) sediments (from 402 patients) were tested in parallel by both assays. The results were compared with those of acid-fast staining and culture (solid plus liquid media), setting the combination of culture and clinical diagnosis as the "gold standard." Culture results from the tested specimens were as follows: 121 Mycobacterium tuberculosis complex (MTB) (98 smear-positive), 46 nontuberculous mycobacteria (38 smear-positive), and 338 culture-negative results. After resolution of the discrepant results, the percent sensitivity, percent specificity, and positive and negative likelihood ratios for AMTDII were 88%, 99.2%, 110, and 0.11 for respiratory specimens and 74.3%, 100%, 740, and 0.26 for extrapulmonary specimens, respectively. The corresponding values for DTB were 94.5%, 99.6%, 235, and 0.05 for respiratory specimens and 92.3%, 100%, 920, and 0.07 for extrapulmonary specimens, respectively. The cumulative difference for all tuberculosis-positive extrapulmonary specimens was significant (P ‫؍‬ 0.03). The overall inhibition rate for DTB was 5% (26 specimens). We conclude that both amplification assays proved to be rapid and specific for the detection of MTB in clinical samples and particularly feasible for a routine laboratory work flow. DTB combines a labor-intensive specimen preparation procedure with a completely automated amplification and detection. Finally, differences between AMTDII and DTB sensitivities were associated with the presence of inhibitory samples that the former assay, lacking IAC, could not detect.Tuberculosis (TB) continues to be a global public health problem. In industrialized countries, four main conditions are currently referred to as promoting the spread of TB: human immunodeficiency virus pandemic, immigration from high-TBprevalence areas, the worsening of economic and social conditions (including an increase in homelessness), and the emergence of multidrug-resistant strains. Successful TB control depends on effective case finding and rapid detection of Mycobacterium tuberculosis complex (MTB). Conventional methods include staining smears for acid-fast bacilli (AFB) and culture by liquid and solid media. However, AFB staining lacks sensitivity and specificity, whereas culture results are usually not available earlier than 2 to 3 weeks.Because of their theoreti...

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Evaluation of conventional molecular diagnosis of Mycobacterium tuberculosis in clinical specimens from Morocco

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