Using one of the most detailed analyses ever undertaken into biological markers for tuberculosis (TB), researchers at the UK’s University of Southampton, working with colleagues from across the world, have identified a group of six biomarkers to help diagnose patients. Speaking to Katherine Price, lead author Dr Hannah Schiff shares her ambitions for these findings to pave the way for new lateral flow tests to diagnose more people with TB, diagnose them earlier and stop the infection from spreading.
Tuberculosis (TB) is the world’s deadliest infectious disease, killing more than one million people each year. An estimated 10.6 million people fell ill with TB in 2022, according to the World Health Organization (WHO). A disease often associated with health inequality, risk factors include smoking, alcohol abuse, HIV infection and malnourishment.
Europe accounted for 2% of all cases, according to the WHO data, and here it remains a public health issue despite most countries being low incidence. This is due to it predominantly affecting vulnerable populations such as migrants, prison inmates and people coinfected with HIV. In England, nearly 5,000 cases were recorded in 2023, with cases on the rise.
Closing diagnosis gaps is key in reducing incidence. However, in 2021, there were an estimated 3.7 million missed cases globally. Diagnostic delays, particularly in low- and middle-income countries, and funding for prevention, diagnostics and treatment fell far short of the globally estimated need and UN targets.
Treatment success rates in Europe also remain far below regional targets, and have in fact decreased, indicating increasing challenges to delivery of care. Up to half of patients do not complete treatment courses, according to one US study, which often last several months or even years for multidrug-resistant TB, even if they do get a diagnosis.
Closing the TB case-diagnosis gap
‘That’s the driver, to try and close that case-diagnosis gap and finding the missing millions,’ says Dr Hannah Schiff, a National Institute for Health and Care Research (NIHR) academic clinical lecturer and speciality registrar in respiratory medicine at the University of Southampton. She is also the lead author on a new study that has identified tuberculosis-specific diagnostic biological markers.
Fascinated with the lungs, Dr Schiff trained at the John Radcliffe Hospital in Oxford and the Royal Berkshire Hospital in Reading, UK, before embarking on her specialist respiratory training at Southampton. ‘They’re just an amazing body organ to study,’ she says. ‘It’s such an interface for infection and I’ve always been interested in infections and the host and pathogen interaction. Why does the same bug cause slightly different disease in different people? And TB is a case in point for that – there are so many host factors that alter how lung disease manifests.’
Currently, TB diagnosis commonly relies on sputum samples, which not all patients can produce, as well as the necessary infrastructure and skilled operators for analysis. Patients with TB can also have a negative sputum smear microscopy and culture result – the latter of which can take several weeks to return, and these approaches haven’t changed for decades, says Dr Schiff.
While molecular testing for TB DNA has emerged over the last decade, this also relies on sputum samples and therefore suffers from the same limitations.
‘Making the diagnosis is the biggest block to the entire care cascade, and once a diagnosis is made, then you’re most of the way there,’ she explains.
The possibility of proteins
Dr Schiff and her colleague, senior author Professor Paul Elkington, developed their research to address the urgent need for accurate point-of-care testing that doesn’t rely on sputum expectoration or specialist equipment.
Their latest study, supported by the NIHR and UK Medical Research Council and published in the Journal of Clinical Investigation Insight, shows the potential for host proteins to support diagnostics. It was a team effort drawing on global expertise.
From the NIHR Southampton Biomedical Research Centre, senior author Dr Diana Garay-Baquero, a chemist originally from Colombia, led the proteomics work under the supervision of US-based proteomics expert Dr Spiros Garbis.
Dr Naomi Walker, infectious disease specialist and a researcher at the Liverpool School of Tropical Medicine, contributed a cohort of South African samples, and Marc Tebruegge in Vienna contributed a UK-based cohort. Bioinformatics data collection was overseen by the University of Southampton’s Dr Andres Vallejo and US-based Dr Christopher Woelk, while the University of Oxford supported with the validation phase. The study was also undertaken with experts from South Africa’s University of Cape Town and Cayetano Heredia University in Peru.
‘It was really inspiring to work with people globally [who] just have such a variety of background experience and can bring so much to the project,’ says Dr Schiff.
The academics used a proteomics technique that doesn’t remove albumin, which Dr Schiff says can inadvertently remove proteins of biological interest. The team believes it’s one of the most detailed analyses ever undertaken of biomarkers for TB.
Proteins are excellent candidates for diagnostic biomarkers, being stable and utilisable for near-patient diagnostic tests. However, while several studies have explored the potential of host plasma protein biomarkers for TB diagnosis, and numerous candidate proteins have been detected, biomarkers or combinatorial biomarker signatures had not yet been found that could reliably differentiate TB from other respiratory diseases or predict progression.
Dr Schiff and her team of researchers applied a highly sensitive non-depletion tandem mass spectrometry discovery approach and bioinformatic analysis. Using linear modelling and network correlation analyses, they identified 118 differentially expressed proteins. These were then narrowed down to six that could distinguish contagious TB from healthy controls and other respiratory infections.
Paving the way for a simpler, faster TB test
The researchers hope these six blood proteins will pave the way for the development of an affordable, sensitive, specific, user-friendly and rapid point-of-care test that could be used in resource-limited settings. Dr Schiff says this could be particularly helpful for case finding and reducing TB rates in communities of high disease instance.
However, next steps will be largely dependent on funding, and she says the next realistic milestone will probably be at least a few years down the line.
‘At the moment, measuring the markers needs sequencing and very highly specialised laboratory equipment,’ she explains. ‘We’re planning experiments to do it in a lower-level lab facility with more standard equipment… to try and get it onto a device that could be used at point-of-care.’
The idea is to leverage diagnostics innovation that emerged during the Covid-19 pandemic, such as at-home lateral flow testing. ‘The dream would be if you could get these markers onto a lateral flow test. That would be ideal, but you need a device that can measure several markers, not just one, and with enough sensitivity and a semi-quantitative readout, not just a yes/no answer,’ adds Dr Schiff. ‘But if we could translate this into use in the field, that’s where it would have the most benefit.’
This could then help close the case-detection gap that fuels the global TB pandemic. ‘There shouldn’t be people in this world that are suffering from a disease that is curable and treatable, just for want of a diagnosis,’ says Dr Schiff.
Developments, challenges and opportunities
Dr Schiff is currently working on further analysis of the proteomic datasets to explore variation of protein markers by host phenotypic characteristics and how these might be harnessed to improve diagnostic sensitivity.
Her colleague Dr Liku Tezera, who worked on the biomarker research, has developed a 3D TB infection cell culture model, which could be used to look at some of the identified biomarkers and explore their potential pathological role in TB infection, Dr Schiff explains. The TB clinic is also continuing to source samples from patients with active pulmonary disease, with help from a TB nursing team.
Wider developments in scaling up shorter treatment regimens, meanwhile, are believed to be behind the success rates for rifampicin-resistant TB that are slowly but consistently improving in Europe.
‘The key is having healthcare system support, your TB nursing team, and lines of communication and support open with the patients,’ says Dr Schiff. ‘We know what drugs work and we know the regimes. The challenges are getting people a timely diagnosis and successfully through the whole course of treatment.’
