Performance of GeneXpert Assay in Detecting Pulmonary Tuberculosis and Rifampicin Resistance in Patients Attending Kitui County Hospital, Kenya

Abstract

Background: To combat the challenges of TB epidemic in Kenya there has been massive scale up of both treatment and diagnostic facilities.The challenges encountered in these centers is failure to accurately detect Mycobacterium tuberculosis. In this work, we aimed at evaluating the performance of GeneXpert MTB/RIF assay in detection of pulmonary TB and drug resistant testing. Methods: Smear microscopy, niacin test, culture and GeneXpert MTB/RIF assay were used to test for the presence of Mycobacterium tuberculosis in 400 patient’s sputum samples. Drug susceptibility testing was done using the culture method and GeneXpert MTB/RIFassay. Results: Out of the 400 samples analysed 37.5% were smear positive of which 60% (p<0.05) were male. For the culture and GeneXpert assays the positive samples were 33% and 32.25% respectively. Smear microscopy had the highest number of false positives (28%) and false negatives (9.6%). For bacilli identification the sensitivity, specificity, positive predictive value and negative predictive values for smear microscopy were 81.8%, 84.3%, 72% and 90.4% while for GeneXpert they were 97.7%, 100%, 100% and 98.9% respectively. This implies that GeneXpert was a better method. Drug susceptibility testing using the culture method showed that 23 isolate were rifampicin resistant and with GeneXpert they were 26, implying 3 false positives. The sensitivity, specificity, positive predictive value and negative predictive value for GeneXpert assay in drug susceptibility testing was 100%, 97%, 89% and 100%. Cost of testing samples with GeneXpert assay was higher than culture but it offers rapid detection in that on average it took between 2 hours against up to 8 weeks for the culture method. Conclusion: GeneXpert MTB/RIF assay offers high potential for rapid diagnosis of TB and drug susceptibility testing in an austere Kenyan environment.