Focusing on people who lived with someone with active TB, the research team enrolled 4,466 HIV-negative, healthy study participants from the households of 1,098 index cases (people with active TB, who allowed the researchers to enroll members of their household who did not have TB in its active stage). Blood samples were taken from the 4,466 study participants and stored.
At the end of the initial study period, when it was apparent who had progressed to TB and who hadn’t, the blood samples of 79 individuals who progressed to active TB between 3 and 24 months following exposure, and 328 who remained healthy during the 2 years of follow up, were analyzed. (Due to the cost of the tests, the blood samples of the other study participants were not tested.) Various biosignatures – combinations of gene or protein levels that together result in a test readout that relates to current or future risk for developing the condition – were measured.
“The individual components of this signature may not be sufficient to deliver an accurate diagnosis of prediction, but a combination of these markers improves its accuracy,” said Prof. Walzl.
A number of companies have the ability to develop tests that measure the presence of these four genes. “We are hoping that primary health clinics will be able to use such a test and the reagents would then be readily available in that format, similar to the tests that are currently used to diagnose TB,” added Prof. Walzl.
While there are currently tests on the market that may predict progression to TB, the test developed by Prof. Walzl and colleagues gives positive results for a smaller percentage of high-risk household contacts than the current tests. This translates to fewer people being treated unnecessarily in order to prevent TB.
“Preventative treatment is several weeks long and has potential side effects,” explained Prof. Walzl. “One wants to limit the number of people who have to undergo such treatment to those most likely to be at risk for developing active TB.”
Tuberculosis, caused by infection with Myobacterium tuberculosis (M.tb), is the world’s leading cause of death brought on by a single pathogen. More than 10 million new cases of TB are diagnosed each year, and almost two million people die from the disease. Globally, 1.7 billion people are estimated to be infected with M.tb.