Diagnosis of latent tuberculosis infection: The tuberculin skin test and interferon gamma release assays

The clinical manifestations of tuberculosis (TB) represent a complex interaction between the causative organism, Mycobacterium tuberculosis, and the human host immune response.[1] TB is the most common cause of infectious disease-related mortality worldwide after the human immunodeficiency virus (HIV). The World Health Organization (WHO) estimates that 2 billion people are infected worldwide, and according to the 2010 global TB report, there were an estimated 9.4 million incident cases of TB with 12% of these occurring in HIV-positive patients.[2] The bulk of this disease burden resides in sub-Saharan Africa and the majorities of these infections are asymptomatic and may reactivate later in life. This huge global reservoir is termed latent tuberculosis infection (LTBI) and constitutes an important source of infection and a continuous source of transmission. The goal of testing for LTBI is to identify individuals who are at increased risk for the development of TB and therefore would benefit from treatment. Currently, there is no available gold standard or confirmatory test for the diagnosis of LTBI and available surrogates are not without limitations with respect to technical issues with test performance, cost, specificity, sensitivity, effect of Bacille Calmette-Guérin (BCG) vaccine, and environmental mycobacteria. LATENT TUBERCULOSIS INFECTION