The Nitrate Reductase Assay in the Rapid Detection of Multidrug-Resistant and Extensively Drug- Resistant Tuberculosis in South Gujarat, India

Introduction The burden of Tuberculosis (TB) particularly with multi-drug-resistance (MDR) is increasing worldwide and has become a major public health concern. The increasing prevalence of MDR as well as extensively drug-resistant (XDR) tuberculosis highlights the need for simple, rapid, affordable and accurate methods for performing drug susceptibility testing against first- line and second- line anti- TB drugs. Aims To evaluate the performance of NRA in the rapid detection of multi-drug resistant and extensively-drug resistant tuberculosis in the region of South Gujarat, India. Materials and Methods 234 samples were collected from clinically suspected TB patients from South Gujarat Region, India and were subjected to microscopy examination by ZN method, culturing on Lowenstein-Jensen medium and drug susceptibility testing by indirect NRA. Indirect NRA was performed on the culture isolates and the results were compared with that of the Proportion method. Results Out of these 234 samples, 94 were smear positive by Ziehl Neelsen (ZN) method (40.17 %) and 140 were smear negative. In case of culturing, out of 234 samples, 101 were culture positive (43.16 %) and 133 were culture negative. By performing First-Line DST, MDR-TB was detected in a total of 37/101 (36.63 %) and 35/101 (34.65 %) by both Proportion method and NRA respectively. By performing Second-Line DST, one case of XDR-TB was detected by both the methods. NRA results were available for 33 samples on day 7, 58 samples on day 10 and 10 samples on day 14. As compared to Proportion method, the sensitivity of NRA was 87.5 % and 100 % and the specificity was 100 % and 96.73 % for RIF and INH respectively. Similarly, for K and OF, the sensitivity of NRA was 71.42 % and 76.92 % and the specificity was 100 % and 100 % respectively. Conclusion NRA is a simple, accurate, inexpensive and rapid method for detection of MDR and XDR-TB, especially in poor-resource countries, with limited laboratory facilities. The technique may become a valid substitute to traditional time consuming methods.