Performance characteristics of Abbott RealTime-MTB and RealTime INH/RIF-Resistance Assays for direct detection of M. tuberculosis and genetic resistance markers
23 February 2017 (online)
Abbott RealTime MTB (RT MTB) is a new commercial automated nucleic acid amplification-based test for the detection of Mycobacterium tuberculosis complex (MTBC) in clinical specimens. In combination with the Abbott RealTime MTB INH/RIF Resistance (MTB INH/RIF) assay, which can be applied to RT MTB positive specimens in a reflex mode, the tests also indicate genetic markers of resistance to isoniazid and rifampicin. We tested 715 pre-characterized clinical specimens (412 culture negative specimens, 50 specimens growing non-tuberculous mycobacteria [NTM], 85 smear-negative and 168 smear-positive specimens growing MTBC) with the RT MTB. Positive samples were analyzed in a reflex mode with the MTB INH/RIF assay. Based on culture as method of comparison, the overall sensitivity of RT MTB was 92.1%; the sensitivities for smear-positive and smear-negative samples were 100% and 76.4%, respectively. Sensitivity rates for smear-negative specimens were almost identical for respiratory (46/60; 76.6%) and extra-pulmonary (19/25; 76%) specimens. RT MTB showed 100% (412/412) specificity with culture negative specimens and 96% (48/50) specificity with specimens which grew NTM. RT MTB INH/RIF was applied to all 235 samples which were positive with RT MTB and yielded 189 (80.4%) valid results. Resistance pattern were not reported for 46 (19.6%) samples due to signals below the limit of detection. The RT MTB INH/RIF assay identified ten (4.3%) cases with multi-drug resistance, eight (3.4%) with isoniazid resistance and 171 (72.7%) with no resistance markers for isoniazid or rifampicin. Concordance with resistance patterns obtained by Genotype MTBDRplus (HAIN Lifescience, Germany) and phenotypic drug susceptibility testing in MGIT was 100%. The RT MTB is a very specific and sensitive assay for the diagnosis of TB and accurately indicates potential resistance markers. It is a great asset for high through-put diagnostics of TB or for settings were DR-TB is frequent.