Abstract
The MTBDRplus (Hain Lifescience, Nehren, Germany) is a molecular assay detecting mutations involved in M. tuberculosis rifampicin (RMP) and isoniazid (INH) resistance, approved for application on culture isolates and smear-positive (AFB+) specimens1.We evaluated its performance as a routine diagnostic assay directly on clinical specimens.
Methods: Consecutive AFB+ and selected AFB- specimens, from high risk patients for drug resistance, were assayed. The results were compared to conventional drug susceptibility testing (DST). For time reduction estimation we counted the days elapsed before patient's first positive culture was available. Results: 475 specimens were analyzed. Interpretable MTBDRplus results were obtained for 331/400 (82.7%) AFB+, 33/70 (47%) AFB- and 1/5 (20%) microscopically suspicious specimens. We identified: 13 MDR, 28 INH resistant, 2 RMP resistant, and 2 rpoB polymorphic strains. Disagreement between DST and MTBDRplus mainly involved strains with inhA mutations (6/8) conferring resistance to low INH concentrations2. The sensitivity, specificity, PPV and NPV values for RMP and INH resistance detection were 100%, 99, 6%, 92, 8%, 100% and 86, 6%, 96, 9%, 79%, 94% respectively. Substantial reduction in drug susceptibility diagnosis was recorded (14.1 ± 6.2 days).
Conclusions: The MTBDRplus assay was informative for the great majority of AFB+ cases, highly accurate for screening RMP and INH resistance and its application achieved considerable reduction in diagnostic delay.
1Hillemann D. et al. J. Clin. Microbiol. 2007, 45: 2635–2640
2Hongling G. et al. J. Med.Microbiol. 2006, 55: 1527-1531.
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