Early Blood Test Detects Silent Tuberculosis in High-Risk Contacts

Tuberculosis (TB) can be a quiet, slowly developing disease, and that silence makes it hard to find before symptoms appear. Underdiagnosis is a major problem, especially among people who live with someone newly diagnosed with TB. Researchers followed household contacts of newly diagnosed TB patients for two years to see who developed TB and who stayed healthy. In this study, participants who later developed TB were labeled Progressors and those who did not were called Non-progressors. The team, led by corresponding author Luke Elizabeth Hanna, looked for tiny fragments of Mycobacterium tuberculosis (Mtb) DNA circulating in the blood as a way to spot infection that standard tests might miss. By focusing on blood-based markers, the researchers aimed to find a practical route to detect disease earlier in people at high risk, including forms of TB that do not always show up in standard respiratory tests. The work seeks to fill a gap in current diagnostics by identifying infection before it becomes clinically obvious, offering a window of time that might allow for earlier care or closer monitoring.

The study tested plasma for Mtb ccfDNA by targeting the insertion sequences IS6110 and IS1081 using ddPCR. This laboratory approach allowed the team to detect small amounts of bacterial DNA in blood samples. In people with subclinical TB—those who had infection but not yet overt symptoms—the assay showed a sensitivity of 90.9%. For cases classified as possible TB, the sensitivity was 81.8%. Importantly, the test picked up Mtb ccfDNA in Progressors as early as six months before clinical TB diagnosis, with a sensitivity of 79.0%. In roughly 55.0% of cases, Mtb ccfDNA was detectable 12 months before active disease, and in about 50.0% it was detectable 18 months before disease developed. The test also performed very well for extra-pulmonary TB, showing 100.0% sensitivity up to six months prior to disease onset. These results indicate that measuring Mtb ccfDNA with ddPCR and the IS6110 and IS1081 targets can reveal infection well before standard clinical diagnosis in a substantial fraction of high-risk individuals.

The findings point to a promising tool for spotting TB earlier among people who are most likely to develop disease: household contacts of newly diagnosed patients. Detecting Mtb ccfDNA months or even more than a year before symptoms appear could change how clinicians monitor high-risk groups, offering a chance to intensify follow-up or begin diagnostic evaluation sooner. The strong performance in extra-pulmonary TB is especially notable because those cases can be missed by traditional respiratory tests. While the study focuses on detection rather than treatment, earlier identification of subclinical infection could help prioritize who needs closer clinical attention or further testing. Before such a test is widely adopted, additional work would be needed to confirm these findings in larger and diverse populations and to define how best to act on early positive results. Nonetheless, this approach using Mtb ccfDNA, IS6110, IS1081, and ddPCR provides a clear direction for improving TB diagnosis in diagnostically challenging cohorts.