Evaluation of Nitrate Reductase Assay for Detection of Multi-drug Resistant Mycobacterium tuberculosis among Patients at National Tuberculosis Reference Laboratory Zaria Nigeria

Aims: To evaluate nitrate reductase assay for detection of multi-drug resistant Mycobacterium tuberculosis among patients at National Tuberculosis Reference Laboratory Zaria Nigeria.

Study Design: Hospital based cross sectional study

Place and Duration of Study: National Tuberculosis Reference Laboratory Zaria Nigeria from December 2015 to June 2016.

Methodology: A total of 437 re-treatment patients’ samples were screened for Acid Fast Bacilli (AFB), 72 were smear positive. Out of 72 smears positive, 62 were culture positive, using Lowenstein Jensen medium, 57 were found to be Mycobacterium tuberculosis complex (MTBC) using immunochromatographic test. In this study the susceptibility of 57 MTBC isolates to isoniazid (INH), rifampicin (RIF), streptomycin (STR) and Ethambutol (EMB) was determined by Lowenstein Jensen proportion method (LJPM) and Nitrate Reductase Assay (NRA)

Results: The sensitivity and specificity of NRA compared to that of LJPM were observed to be 98% and 89%, 98% and 92%, 64% and 80%, 68% and 77% for RIF, INH, STR, and EMB respectively. Positive predictive values were 91%, 93%, 87% and 83% for RIF, INH, STR and EMB respectively. Negative predictive values were 80%, 92%, 67% and 90% for RIF, INH, STR and EMB respectively .Overall, the sensitivity, specificity ,positive predictive value and negative predictive value of NRA in detecting MDR-TB were 90%,82%,85%and 73% respectively. Good agreement was found in all the tests with κ values of 0.63, 0.61, 0.61 and 0.62 for RIF, INH, EMB and MDR-TB respectively only STR shows moderate agreements with k value of 0.59.

Conclusion: In the emergence of MDR-TB, the NRA may be of great importance due to its higher sensitivity and specificity for the rapid detection of rifampicin and isoniazid resistance, the two most important drugs for tuberculosis treatment. On the basis of our findings, NRA has the potential to be a useful tool for accurate detection of MDR-TB in the study area.