Evaluation of a Novel Microbiological Diagnostic Test for Latent Mycobacterium Tuberculosis Infection

Tuberculosis (TB) is an infectious disease that is caused by bacteria (bugs). The infection is passed on when a patient with active lung TB coughs bugs into the air, which are then breathed in by an uninfected person. In 90% of people who get infected, the TB infection remains dormant and the person never falls ill with active TB disease. However, 10% of people with dormant TB infection will eventually go on to develop active TB disease at some time in the future, with symptoms such as cough and weight loss. Dormant TB infection can be treated with a 3-month course of antibiotics, which prevent the infection from becoming active and causing problems in the future. However, existing tests for dormant TB rely on detecting the body's immune response to infection, rather than detecting the TB bugs themselves. Because the immune response doesn't go away when dormant TB is treated, existing tests for dormant TB do not change from positive to negative after antibiotic treatment. Thus, clinicians can't know if antibiotic treatment of dormant TB infection was successful or not. Moreover, existing tests can't distinguish the 90% of people with dormant TB infection who will never develop active TB (and who don't need antibiotics) from the 10% who will go on to fall ill with active TB at some point in the future (who do need antibiotics). So the investigators end up giving antibiotics to many more people than we need to. Recently, a group of scientists in Germany have developed a sensitive new blood test that was able to detect very small numbers of TB bugs in the blood of just seven people with dormant TB infection. This finding has created a lot of excitement in the TB field, as nobody has been able to find TB bugs in people with dormant infection before. Our research study will evaluate this new blood test in a larger group of 100 people, with and without dormant TB infection, to see if the findings from Germany are really true. If they are, then this could lead to the dev