DIAgnostics for Multidrug Resistant Tuberculosis in Africa

Overview

Recent advances in molecular diagnostics of tuberculosis, especially the GeneXpert Mycobacterium tuberculosis/Rifampicin test have reduced the time to diagnose Rifampicin Resistant Tuberculosis (RR-TB) but only rifampicin resistance is diagnosed, leading to presumptive diagnosis of resistance to isoniazid and maybe other drugs. Thus in low and middle income countries, most drug sensitivity testing relies on phenotypic drug resistance testing, which takes up to 4 months. In addition, currently, culture on monthly sputum samples is recommended by the World Health Organization for follow-up of Rifampicin Resistant Tuberculosis patients under treatment. Unfortunately, culture is often not locally available and samples need to be transported from field to culture laboratories. The associated transport delays lead to high rates of contamination and false negative culture, particularly in laboratories in low resource settings. Many gaps for the diagnosis and management of RR-TB patients still need to be addressed and the DIAMA project (DIAgnostics for Multidrug resistant tuberculosis in Africa) study aims to address some of them.

The proposed DIAMA (DIAgnostics for Multidrug resistant tuberculosis in Africa) study aims to address current gaps in the diagnosis and management of patients with Multi-Drug-Resistant (MDR) tuberculosis. Building on existing networks and research collaborations previously funded by the European \& Developing Countries Clinical Trials Partnership (EDCTP), this project involved partners in West, Central, and East Africa. It aims to evaluate and implement rapid and accurate molecular tests for several anti Tuberculosis drugs, to replace the current dependency on phenotypic drug resistance testing, which takes up to 4 months and is technically so demanding that few laboratories can perform it correctly. The project builds on the continuous surveillance of Tuberculosis retreatment patients for rifampicin resistance. Two African partners (Benin and Rwanda) with advanced molecular laboratories are establishing reference laboratories for the 'Deeplex' assay, a novel multiplex deep sequencing-based drug resistance diagnostic platform that simultaneously provides sequence information of genes that confer resistance to several key anti tuberculosis drugs. Partners are recruiting all patients with rifampicin resistant Tuberculosis, and a subset of those with rifampicin sensitive Tuberculosis. In a first phase, sputum will be shipped for the Deeplex assay, for comparison against phenotypic DST, the reference method for detecting resistance to 1st and 2nd line drugs. In addition, since Whole Genome Sequencing is the "reference" of molecular tests, Deeplex assay will also be validated again this test. In a second phase, Cepheid 2nd line Xpert and Molbio Truenat test, two 'lower tech' tests at the last stages of laboratory validations, will also be validated. The Cepheid Xpert 2nd line cartridge can be implemented in existing Xpert machines used for the Xpert MTB/Rif assays. These tests will be compared versus the Deeplex assay and versus WGS Using the latest advances in DataTocare software developed by one of the project partners, molecular results will be communicated in real time to the National Tuberculosis Programmes, so that Multi Drug Resistant Tuberculosis patients can swiftly start appropriate treatment. The added-value of this system will be evaluated as a pilot study in some sites. Lastly, once patients have initiated MDR treatment, they will be monitored for treatment success by faster alternative approaches to the WHO recommended monthly cultures: serial sputum samples will have Fluorescein DiAcetate (FDA) vital stain microscopy, measurement of the bacterial load using the Xpert MTB/Rif as well as precursor of ribosomal RNA measurement (pre-rRNA). Together, these advances are expected to dramatically improve the currently dismal prognosis of MDR-TB in health systems in resource-poor settings.