Multi-drug resistant tuberculosis (MDR-TB) remains a major challenge for the control of tuberculosis worldwide. Susceptibility testing of Mycobacterium tuberculosis isolates to first line drugs is therefore necessary to ascertain the diagnosis of MDR-TB. A total of 437 re-treatment patients' samples were screened for Acid Fast Bacilli (AFB), 72 were smear positive giving a prevalence of 16.47%. Out of 72 smears positive, 62 were culture positive, 6 were culture negative and 4 were contaminant using Lowenstein Jensen medium. Out of 62 cultures positive, 57 were found to be Mycobacterium tuberculosis complex (MTBC) using immunochromatographic test while 5 were negative which were considered to be NTM (Non-Tuberculosis Mycobacteria).
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). LJ PM detected 41(71.93%) MDR-TB while NRA detected 44(77.19%) MDR-TB isolates. The occurrence of poly resistance to anti-TB drugs using NRA and LJ PM was 12% and 14% while pan susceptible were of 11% and 14% by LJ PM and NRA respectively. The sensitivities and specificities of NRA compared to those of LJPM were observed to be 98% and 98%, 64% and 68%, 89% and 92%, 80% 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 values were 80%, 92%, 67% and 90% for RIF, INH, STR and EMB respectively. Good agreement was found in all the tests with ? values of 0.63, 0.61, 0.59, and 0.61for RIF, INH, STR, and EMB respectively. The HIV/TB co-infections and HIV/MDR-TB co-infections were reported to be 9.7% and 7% respectively. Highest MDR-TB among age groups of 21-30 and 31-40 years were detected by NRA and LJPM and higher MDR-TB and TB were observed in male. The NRA has the potential to be a useful tool for rapid detection of MDR-TB in resource-limited settings because of its higher sensitivity and specificity.
