Tuberculosis latente

Abstract

Tuberculosis continues being a huge public health problem. It has been estimated that worldwide every year about 9 million people adquire the disease and 2 million of deaths are because of tuberculosis. Exposure to Mycobacterium tuberculosis causes active disease in nearly 10% of the people. In the remaining 90% of the exposed population the immune response inhibits M. tuberculosis multiplication. In part of the exposed people (~40%) some bacilli are not killed remaining in a non-replicating condition, generating the so called latent tuberculosis infection. The inactive bacilli can regain their vitality (replication capacity) and cause active tuberculosis if the immune response is disrupted. Targeted screening and treatment for latent tuberculosis infection has been recognized as an effective strategy for tuberculosis control. Until recently, the only test available for the detection of latent tuberculosis infection was the tuberculin (PPD) skin test. Recently it has been developed an in vitro T-cell-based interferon-gamma release assay (IGRA). This assay use antigens specific to M. tuberculosis and is not affected by previous BCG vaccination, making it a useful screening test for latent tuberculosis in BCG-vaccinated populations. FDA has approved two commercial IGRAs: a) QuantiFERON-TB Gold (QFT, Cellestis) which simplified variation is called Quantiferon T in Tube (QFT-G-IT) and b) T-SPOT TB test (Oxford, Immunotec). According to the Chilean National Program of Tuberculosis Control, therapy for latent tuberculosis infection is daily administration of isoniazid for 9 months; administered regularly this therapy gives over 90% of protection. Another option used in USA and Europe is to prescribe rifampicin for 4 months. Identification of latent tuberculosis carriers and their treatment is a pivotal action in the efforts for decreasing tuberculosis incidence in developing countries with low or intermediate rates of tuberculosis incidence.