Evaluation of nitrate reductase assay for rapid detection of resistance to second-line drugs in Mycobacterium tuberculosis in a tertiary care hospital

The present study evaluated nitrate reductase assay (NRA) for rapid detection of resistance to 5 second-line drugs: kanamycin, ethionamide, ofloxacin, cycloserine, and para-aminosalicylic acid. Eighty-six multidrug-resistant clinical isolates of Mycobacterium tuberculosis were used to compare NRA with proportion method for rapid detection of resistance to second-line drugs. The sensitivity of the NRA for different drugs ranged from 86.4% to 100%, whereas the specificity ranged from 98.4% to 100%. Excellent agreement was found between the 2 tests with respect to their κ values. For 63% of the isolates, the results were available in 14 days (turnaround time). The NRA is a rapid, accurate, simple, and inexpensive method for detection resistance to second-line drugs. This method may become an appropriate alternative method, especially for the resource poor settings.