Analytical and clinical evaluation of the Epistem Genedrive Assay for detection of Mycobacterium tuberculosis

Shenai S, Armstrong DT, Valli E, Dolinger DL, Nakiyingi L, Dietze R, Dalcomo MP, Nicol MP, Zemanay W, Manabe Y, Hadad DJ, Marques-Rodrigues P, Palaci M, Peres RL, Gaeddert M, Armakovitch S, Nonyane BAS, Denkinger CM, Banada P, Joloba ML, Ellner J, Boehme C, Alland D, Dorman SE, and the TB Clinical Diagnostics Research Consortium

Abstract

Epistem’s Genedrive® is a nucleic acid amplification test available on the market for tuberculosis diagnosis. In this study, the clinical sensitivity was substantially lower than that of sputum smear microscopy. An analytical study revealed cross-reactivity with some other mycobacteria and biosafety concerns.

Background: The Epistem Genedrive® assay rapidly detects Mycobacterium tuberculosis complex from sputum and is currently available for clinical use. However, the analytical and clinical performance of this test has not been fully evaluated.

Methods: The analytical limit of detection (LOD) of the Genedrive PCR amplification was tested with genomic DNA; performance of the complete (sample processing plus amplification) system was tested by spiking M. tuberculosis mc26030 cells into distilled water and M. tuberculosis-negative sputum. Specificity was tested using common respiratory pathogens and non-tuberculosis mycobacteria. A clinical evaluation enrolled adults with suspected pulmonary tuberculosis, obtained three sputa from each participant, and compared Genedrive accuracy to that of the Xpert MTB/RIF assay, using M. tuberculosis cultures as the reference standard.

Results: The Genedrive assay had an LOD of 1pg/μl (100 genomic DNA copies/reaction). The LOD of the system was 2.5×104CFU/mL and 2.5×105CFU/mL for cells spiked into water and sputum, respectively. False positive rpoB probe signals were observed in 3/32(9.4%) negative controls as well as for M. abscessus, M. gordonae and M. thermoresistibile. In the clinical study, among 336 analyzed participants, overall sensitivities for tuberculosis case detection of Genedrive, Xpert and smear microscopy were 45.4% (95%CI: 35.2, 55.8), 91.8% (95%CI: 84.4, 96.4) and 77.3% (95%CI: 67.7, 85.2) respectively. Sensitivities of Genedrive and Xpert for detection of smear microscopy-negative tuberculosis were 0% (95%CI: 0, 15.4) and 68.2% (95%CI: 45.1, 86.1) respectively.

Conclusion: The Genedrive assay did not meet World Health Organization-recommended performance standards for a smear microscopy replacement tuberculosis test. Epistem is working on modifications to improve the assay.

 

Read at J Clin Microbiol