Validation of the GenoType(R) MTBDRplus assay for diagnosis of multidrug resistant tuberculosis in South Vietnam

ABSTRACT: BACKGROUND: To control multidrug resistant tuberculosis (MDR-TB), the drug susceptibility profile is needed to guide therapy. Classical drug susceptibility testing (DST) may take up to 2 to 4 months. The GenoType(R) MTBDRplus test is a commercially-available line-probe assay that rapidly detects MTB complex, as well as the most common mutations associated with rifampin and isoniazid resistance. We assessed sensitivity and specificity of the assay by using a geographically representative set of MTB isolates from the South of Vietnam. METHODS: We re-cultured 111 MTB isolates that were MDR, rifampin-resistant or pan-susceptible according to conventional DST and tested these with the GenoType(R) MTBDRplus test. RESULTS: By conventional DST, 55 strains were classified as MDR-TB, four strains were rifampicin mono-resistant and 52 strains were susceptible to all first-line drugs. The sensitivity of the GenoType(R) MTBDRplus was 93.1% for rifampicin, 92.6% for isoniazid and 88.9% for the combination of both; its specificity was 100%. The positive predictive value of the GenoType(R) MTBDRplus test for MDR-TB was 100% and the negative predictive value 90.3%. CONCLUSION: We found a high specificity and positive predictive value of the GenoType(R) MTBDRplus test for MDR-TB which merits its use in MDR-TB treatment program in Vietna