Evaluation of nitrate reductase assay for early detection of multi and extensively drug resistance tuberculosis in our setup

Objective: To evaluate the performance of nitrate reductase assay on smear positive pulmonary specimens for detection of multi and extensively drug resistant tuberculosis simultaneously. Study Design: Cross-sectional analytical study. Place and Duration of Study: Microbiology Department, Armed Forces Institute of Pathology, Rawalpindi from June to December 2016

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Methodology: Smear positive pulmonary samples were processed both by nitrate reductase method on Lowenstein Jenson medium and also inoculated on gold standard Bactec MGIT 960 TB system. All the specimens were first digested and decontaminated according to standard protocol before inoculation

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Results: Out of total 76 samples, three did not give color and, therefore, were excluded from the final data analysis. Among the remaining 73 samples, mycobacterial index was: 28 specimens were having 1+ [1-9 bacilli/100 fields], 26 samples were 2+ [1-9 bacilli/ field], and 19 samples were having 3+ index [>9 bacilli/field]. The respective sensitivity and specificity were 84% and 100% for isoniazid [INH]; 82% and 100% for rifampin [RIF]; 67% and 100% for amikacin [AK]; and both 100% for ofloxacin [OFX]. Overall agreement in case of INH, RIF, AK, and OFX was 94.5%, 97.2%, 98.6% and100%, respectively. Overall average agreement was 97.5%

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Conclusion: Nitrate reductase assay is a reliable, low cost and accurate method that can be used for early for diagnosis of multi and extensively drug resistant tuberculosis