Analytical and Clinical Evaluation of the Epistem Genedrive Assay for Detection of Mycobacterium tuberculosis

Abstract

The Epistem Genedrive assay rapidly detects the Mycobacterium tuberculosis omplex from sputum and is currently available for clinical use. However, the analytical and clinical performance of this test has not been fully evaluated. The analytical limit of detection (LOD) of the Genedrive PCR amplification was tested with genomic DNA; the performance of the complete (sample processing plus amplification) system was tested by spiking M. tuberculosismc(2)6030 cells into distilled water andM. tuberculosis-negative sputum. Specificity was tested using common respiratory pathogens and nontuberculosis mycobacteria. A clinical evaluation enrolled adults with suspected pulmonary tuberculosis, obtained three sputum samples from each participant, and compared the accuracy of the Gene drive to that of the Xpert MTB/RIF assay using M. tuberculosiscultures as the reference standard. The Genedrive assay had an LOD of 1 pg/μl (100 genomic DNA copies/reaction). The LODs of the system were 2.5 × 10(4)CFU/ml and 2.5 × 10(5)CFU/ml for cells spiked into water and sputum, respectively. False-positiverpoBprobe signals were observed in 3/32 (9.4%) of the negative controls and also in few samples containing Mycobacterium abscessus,Mycobacterium gordonae, o rMycobacterium thermoresistibile In the clinical study, among 336 analyzed participants, the overall sensitivities for the tuberculosis case detection of Gene drive, Xpert, and smear microscopy were 45.4% (95% confidence interval [CI], 35.2% to 55.8%), 91.8% (95% CI, 84.4% to 96.4%), and 77.3% (95% CI, 67.7% to 85.2%), respectively. The sensitivities of Gene drive and Xpert for the detection of smear-microscopy-negative tuberculosis were 0% (95% CI, 0% to 15.4%) and 68.2% (95% CI, 45.1% to 86.1%), respectively. The Genedrive assay did not meet performance standards recommended by the World Health Organization for a smear microscopy replacement tuberculosis test. Epistem is working on modifications to improve the assay.