Performance of the MTBDRsl assay in Georgia

SETTING: The country of Georgia has a high burden of multi- (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB). OBJECTIVE: To assess the performance of the GenoType® MTBDRsl assay in the detection of resistance to kanamycin (KM), capreomycin (CPM) and ofloxacin (OFX), and of XDR-TB. DESIGN: Consecutive acid-fast bacilli smear-positive sputum specimens identified as MDR-TB using the MTBDRplus test were evaluated with the MTBDRsl assay and conventional second-line drug susceptibility testing (DST). RESULTS: Among 159 specimens, amplification was adequate in 154 (97%), including 9 of 9 culture-negative and 2 of 3 contaminated specimens. Second-line DST revealed that 17 (12%) Mycobacterium tuberculosis isolates were XDR-TB. Compared to DST, the MTBDRsl had 41% sensitivity and 98% specificity in detecting XDR-TB and 81% sensitivity and 99% specificity in detecting OFX resistance. Sensitivity was low in detecting resistance to KM (29%) and CPM (57%), while specificity was respectively 99% and 94%. Median times from sputum collection to second-line DST and MTBDRsl results were 70-104 vs. 10 days. CONCLUSION: Although the MTBDRsl assay had a rapid turnaround time, detection of second-line drug resistance was poor compared to DST. Further genetic mutations associated with resistance to second-line drugs should be included in the assay to improve test performance and clinical utility.