Rapid progress has been made in the development of new diagnostic assays for tuberculosis in recent years. New technologies have been developed and assessed, and are now being implemented. The Xpert MTB/RIF assay, which enables simultaneous detection of Mycobacterium tuberculosis (MTB) and rifampicin (RIF) resistance, was endorsed by WHO in December, 2010. This assay was specifically recommended for use as the initial diagnostic test for suspected drug-resistant or HIV-associated pulmonary tuberculosis. By June, 2012, two-thirds of countries with a high tuberculosis burden and half of countries with a high multidrug-resistant tuberculosis burden had incorporated the assay into their national tuberculosis programme guidelines. Although the development of the Xpert MTB/RIF assay is undoubtedly a landmark event, clinical and programmatic effects and cost-effectiveness remain to be defined. We review the rapidly growing body of scientific literature and discuss the advantages and challenges of using the Xpert MTB/RIF assay in areas where tuberculosis is endemic. We also review other prospects within the developmental pipeline. A rapid, accurate point-of-care diagnostic test that is affordable and can be readily implemented is urgently needed. Investment in the tuberculosis diagnostics pipeline should remain a major priority for funders and researchers.
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The high cost of this technology (similar to that of liquid culture, but far exceeding that of smear microscopy) is seen as a key hurdle to implementation. 66,67 FIND negotiated a discounted pricing structure applicable to 145 high burden and developing countries. 68 A four module GeneXpert platform and linked computer costs about US$17 000 (more than 60% lower than elsewhere). Compared with cartridge costs of roughly $65 in the European Union, discounted costs were initially $18·68 per cartridge when first endorsed by WHO. 69 Costs have since fallen, and with funding from the President's Emergency Plan For AIDS Relief, US Agency for International Development, UNITAID, and the Bill & Melinda Gates Foundation, the cost per cartridge was set at $9·98 from Aug 6, 2012, for the next 10 years. 68
SDL is supported by the Wellcome Trust, UK. PM, MB, MH, and AZ are supported by the European and Developing Countries Clinical Trials Partnership (EDCTP grants REMOX, PANACEA, and TB-NEAT), Netherlands. AZ receives support from the UK Medical Research Council (MRC); UBS Optimus Foundation, Switzerland; University College London Hospitals Comprehensive Biomedical Research Centre (UCLH-CBRC); and the UCLH National Health Service Foundation Trust. This project has been funded in part with federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under contract number HHSN272200800014C, and by the President's Emergency Plan for AIDS Relief (PEPFAR) through the Centers for Disease Control and Prevention. The opinions expressed herein are those of the authors and do not reflect the official views or policies of the US Department of Health and Human Services or the authors' national governments, nor does mention of trade names, commercial practices, or organisations imply endorsement by the US Government or the authors' national governments. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.