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The Big Deal with Diagnostics for Drug-Resistant TB

By guest contributor Reeti Desai Hobson

The stage is set for new diagnostics to accelerate detection of tuberculosis (TB). Against the backdrop of the United Nations General Assembly stakeholder convenings on TB, the World Health Assembly Resolution to Strengthen Global Diagnostics Capacity, and the declaration of the end of the COVID-19 pandemic emergency by the World Health Organization (WHO)—all in the same month—anticipation is growing for the second United Nations high-level meeting (UNHLM) on TB in September 2023. As COVID-19 cases recede, TB is again the top cause of infectious disease deaths globally and there is wider understanding that inequitable access to testing and treatment affects us all.

While TB has sickened people for centuries, newer drug-resistant (DR-TB) versions are more complex and costly to treat, requiring specialized knowledge and resources to address. In 2022, only 60 percent of the estimated 10.6 million people with TB were notified that they had the disease, and of these only one third were tested for DR-TB—leaving the WHO’s End TB goal of universal drug susceptibility testing by 2030 a far reach.   

Despite the daunting challenge, there is global optimism that the political will that united the world to combat the COVID-19 pandemic can also boost research and rollout of the latest diagnostics for DR-TB. The COVID-19 pandemic revealed the importance of rapid and convenient testing and the benefit of “putting diagnostic ownership into patients’ hands,” as Claudia Denkinger shared during a recent McGill University Advanced Diagnostics course. Technological and digital innovations have diffused across all fields of health, and high-quality diagnostics are a boon for DR-TB control.

Advances of note relate to decentralized and point-of-care molecular diagnostics, enabling testing of rural populations despite unstable power or inadequate infrastructure, and advanced triaging tools such as artificial-intelligence read chest X-rays. Portable molecular diagnostics allow patients to receive DR-TB test results in a few days, instead of weeks or months, and reduce the number of patient specimens needed. Often, these innovations are delivered via novel, high-value partnerships between governments and the private sector. Molecular instruments can now conduct simultaneous multi-disease testing, allowing countries to potentially benefit from programmatic cost savings and overcome human resource challenges. Digital health applications closely link testing and treatment, allowing health providers to promptly initiate treatment using more palatable, shorter drug regimens for patients with DR-TB. These actions also provide health systems savings, allowing governments to reprogram the cost of additional months of treatment toward better quality services or additional case-finding.

A laboratory technician prepares samples for testing on a GeneXpert instrument in Pakistan. Photo by IDDS.

These diagnostic advances could be life-changing for the almost half-million people who develop DR-TB annually, but they have yet to reach the most needy patients. The task at hand is to support national TB programs, laboratories, clinicians, all of whom make up the diagnostic front line, to provide timely and accurate testing for DR-TB patients.  USAID’s Infectious Disease Detection and Surveillance (IDDS) project is one such effort, collaborating with governments to increase access to diagnostics and build country capacity for DR-TB testing. The project works with national TB programs to strategically introduce and place new molecular diagnostics such as Molbio Diagnostics’ Truenat® instruments and Cepheid’s GeneXpert® instruments, which use Xpert® MTB/XDR cartridges to detect pre-extensively drug-resistant TB, i.e., TB that is resistant to multiple drugs, including rifampicin and fluoroquinolone.

National TB programs and their partners are also building local capacity for TB drug susceptibility testing for new and repurposed TB drugs, which do not have standardized molecular profiles. This diagnostic gap can be filled by bolstering capacity for phenotypic drug susceptibility testing using broth microdilution or the Becton Dickinson MGIT 960 system. Governments and implementing partners are also paying close attention to potential applications of targeted next generation sequencing, which can be used to analyze the entire Mycobacterium tuberculosis genome to assess resistance across existing and emerging drugs. While genomic sequencing remains cost prohibitive in many countries, requiring significant investment in laboratory workforce and infrastructure, WHO’s upcoming guidance will guide countries on how to harness this technology to strengthen diagnostic networks.

These efforts by governments, researchers, drug development and resource partners, and implementers such as IDDS all contribute to meeting UNHLM targets for TB control and elimination. More funding is needed to improve TB detection and strengthen diagnostic networks in high-burden countries. Already, earlier UNHLM goals remain unmet, due to under-diagnosis of TB patients. Forums such as the UNHLM on TB are opportunities for stakeholders to explore partnerships that mobilize resources and capitalize on global movements such as universal health coverage, pandemic preparedness, and climate change adaptation and mitigation. As the global epidemiology of TB continues trending toward increased drug resistance, working with countries to introduce and integrate the latest diagnostics into diagnostic networks and promptly link patients to appropriate treatments is the only way to meet End TB Strategy and UNHLM goals—and this is quickly becoming the biggest deal of all.  

Reeti Desai Hobson is a senior manager at ICF and deputy director for TB programs for the ICF-led Infectious Disease Detection and Surveillance (IDDS) project, funded by the U.S. Agency for International Development. Reeti is a molecular biologist by training with a graduate degree in International Public Health. She manages and implements infectious disease programs in Africa and Asia, with a focus on diagnostic network and health systems strengthening. The views expressed here are the author’s and not necessarily those of USAID or the U.S. government.

Disclaimer: Views expressed by contributors are solely those of individual contributors, and not necessarily those of PLOS.

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