New tuberculosis diagnostic test detects DNA fragments in blood

Researchers at Tulane University School of Medicine have developed a new, highly sensitive blood test for tuberculosis (TB) that screens for DNA fragments from the Mycobacterium tuberculosis bacteria responsible for the deadly disease.

The test could give doctors a new tool to both quickly identify TB and then assess whether drug treatments are working by monitoring levels of the pathogen’s DNA circulating in the bloodstream, according to a new study published in review The lancet microbe.

Tuberculosis is now the second deadliest infectious disease in the world, behind COVID-19. In 2020, an estimated 10 million people contracted tuberculosis and 1.5 million people died from it, according to the World Health Organization.

Most TB tests rely on screening for sputum, a thick type of mucus from the lungs. But collecting sputum from patients suspected of having TB can be difficult, especially for children. Tuberculosis may also be more difficult to diagnose in immunocompromised HIV patients and in others in whom the infection migrates out of the lungs to other parts of the body. In these extrapulmonary cases, patients may have small bacteria in the sputum, leading to false negatives using current testing methods, said study lead author Tony Hu, PhD, Presidential Weatherhead Chair in biotechnology innovation at Tulane University.

“This test can be a game-changer for tuberculosis diagnostics which not only provides accurate diagnostic results but also has the potential to predict disease progression and monitor treatment,” Hu said. “This will help doctors to intervene early in treatment and reduce the risk of death, especially for children living with HIV.

The study evaluated a CRISPR-based assay that screened cell-free DNA from Mycobacterium tuberculosis bacilli. The screening target is released into the bloodstream and cleared relatively quickly, providing a real-time snapshot of the active infection.

The researchers tested stored blood samples from 73 adults and children with suspected tuberculosis and their asymptomatic household contacts in Eswatini, Africa.

The test identified adult tuberculosis with a sensitivity of 96.4% and a specificity of 94.1% and pediatric tuberculosis with a sensitivity of 83.3% and a specificity of 95.5%. (Sensitivity refers to a test’s ability to diagnose a positive case, while specificity is a measure of a test’s ability to accurately determine a negative case.)

The researchers also tested 153 blood samples from a cohort of hospitalized children in Kenya. These were HIV-positive patients at high risk of tuberculosis and presenting at least one symptom of the disease. The new test detected all 13 confirmed cases of TB and nearly 85% of unconfirmed cases, which were cases diagnosed due to clinical symptoms and not existing gold standard testing methods.

The CRISPR-based test uses a small blood sample and can provide results within two hours.

“We are particularly pleased that the level of Mycobacterium tuberculosis cell-free DNA in HIV-infected children began to decline within a month of treatment, and most of the children’s blood was cleared of bacteria DNA fragments after treatment, meaning that CRISPR-TB has the potential to monitor treatment and will give doctors the ability to better treat TB infections around the world,” Hu said.

The researchers have since adapted the test to a rapid test platform that can deliver results in 30 minutes without any special equipment. The results would be visible on a strip of paper like a rapid COVID-19 test.

“A rapid and highly accurate blood test that could be used anywhere would benefit millions of people living in resource-limited areas with a high TB ​​burden,” Hu said.

Reference: Huang Z, LaCourse SM, Kay AW, et al. CRISPR detection of non-circulating cells Mycobacterium tuberculosis DNA in adults and children, including HIV-positive children: a molecular diagnostic study. The Lancet Microbe. 2022. doi: 10.1016/S2666-5247(22)00087-8.

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