Detection and diagnosis of Mycobacterium tuberculosis

Tuberculosis continues to be a major health problem worldwide, affecting millions of people each year. Accurate and rapid diagnosis is key to controlling the disease, yet the traditional tests for TB produce results that are either inaccurate or take too long to be definitive. A fast and reliable diagnostic method that would differentiate between active and latent TB infection is also lacking. The current routine diagnostic tests for TB - chest x-ray, tissue culture, tuberculin skin test (TST) and acid-fast staining - all have their limitations. A chest x-ray alone is inconclusive; a tissue culture takes too long to produce a result; the TST lacks specificity and reliability; and acid-fast staining depends on a large number of bacteria in the sputum to give an accurate reading. Serological tests using different TB antigens to detect Mycobacterium tuberculosis infection are fast but lack the desired sensitivity. New methods have been developed, such as nucleic acid amplification technology which, although specific, can yield false-positive results. Immunologic tests (QuantiFERON and T-SPOT.TB), which measure the production of IFN-gamma by TB-specific T lymphocytes after encountering M. tuberculosis antigens, have certain advantages over the conventional tests, but they also have their disadvantages and unanswered questions. The need remains for a cost-effective, accurate and rapid method of diagnosing both active and latent TB infection.