BackgroundThe WHO has recommended the implementation of rapid diagnostic tests to detect and help combat M/XDR tuberculosis (TB). There are limited data on the performance and impact of these tests in field settings.MethodsThe performance of the commercially available Genotype MTBDRplus molecular assay was compared to conventional methods including AFB smear, culture and drug susceptibility testing (DST) using both an absolute concentration method on Löwenstein-Jensen media and broth-based method using the MGIT 960 system. Sputum specimens were obtained from TB suspects in the country of Georgia who received care through the National TB Program.ResultsAmong 500 AFB smear-positive sputum specimens, 458 (91.6%) had both a positive sputum culture for Mycobacterium tuberculosis and a valid MTBDRplus assay result. The MTBDRplus assay detected isoniazid (INH) resistance directly from the sputum specimen in 159 (89.8%) of 177 specimens and MDR-TB in 109 (95.6%) of 114 specimens compared to conventional methods. There was high agreement between the MTBDRplus assay and conventional DST results in detecting MDR-TB (kappa = 0.95, p<0.01). The most prevalent INH resistance mutation was S315T (78%) in the katG codon and the most common rifampicin resistance mutation was S531L (68%) in the rpoB codon. Among 13 specimens from TB suspects with negative sputum cultures, 7 had a positive MTBDRplus assay (3 with MDR-TB). The time to detection of MDR-TB was significantly less using the MTBDRplus assay (4.2 days) compared to the use of standard phenotypic tests (67.3 days with solid media and 21.6 days with broth-based media).ConclusionsCompared to conventional methods, the MTBDRplus assay had high accuracy and significantly reduced time to detection of MDR-TB in an area with high MDR-TB prevalence. The use of rapid molecular diagnostic tests for TB and drug resistance should increase the proportion of patients promptly placed on appropriate therapy.

Setting The country of Georgia has a high burden of multidrug and extensively drug-resistant tuberculosis (M/XDR-TB). Objective To assess the performance of the Genotype MTBDRsl assay in the detection of resistance to Kanamycin (KAN), Capreomycin (CAP), Ofloxacin (OFX), and XDR. Design Consecutive AFB smear positive sputum specimens identified as MDR by MTBDRplus testing 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 17 (12%) M. tuberculosis isolates were XDR. Compared to DST, the MTBDRsl had 41% sensitivity and 98% specificity in detecting XDR and an 81% sensitivity and 99% specificity in detecting OFX resistance. Sensitivity was low in detecting resistance to KAN (29%) and CAP (57%) while specificity was 99% and 94%, respectively. Median times from sputum collection to second-line DST and MTBDRsl results were 70–104 versus 10 days. Conclusion The MTBDRsl assay had a rapid turn around time; however 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.