BACKGROUND: To determine the specificity and sensitivity of Gene Xpert MTB/RIF assay and compare it against acid-fast bacillus (AFB) smear microscopy in the diagnosis of pulmonary tuberculosis. METHODS: The study retrospectively compared the results of Gene Xpert MTB/RIF, AFB smear microscopy and AFB culture on respiratory specimens collected from ‘presumptive’ pulmonary tuberculosis patients from June 2014 to September 2015. Only patients for whom all the three test results were available were included in the study. The result of AFB smear and Gene Xpert MTB/RIF were compared to the results of AFB culture which was taken as the reference standard. RESULTS: The sensitivity & specificity of Gene Xpert MTB/RIF was found to be superior to smear microscopy (90.5% & 99.7% against 62.8% & 97.8% respectively). Additionally, 27 patients were detected as having rifampicin resistance using the Gene Xpert assay. Diabetes mellitus, HIV, smoking and presence of cavity(ies) on chest x-ray were identified as important risk factors for multi-drug resistant TB (MDR-TB). CONCLUSION: Gene Xpert outperformed the more commonly used AFB smear microscopy in terms of specificity, sensitivity, positive predictive values (PPV) and negative predictive values (NPV). It was also able to identify drug resistant TB at an early stage. Hence, it has the potential to replace AFB smear microscopy as an initial diagnostic test in “presumptive” pulmonary TB patients.
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