Tuberculosis (TB) is an infectious disease caused by the bacillus Mycobacterium tuberculosis.

The bacteria are spread via airborne droplets when individuals with active pulmonary TB disease cough and expel the bacteria into the air. There are two types of TB conditions: latent TB infection and TB disease. Individuals with latent TB are infected, but have no clinical or radiographic evidence of active disease. Latently infected individuals do not transmit the bacteria. TB disease occurs when manifestations of pulmonary or extrapulmonary TB become apparent, either clinically or on x-ray [1].
Only 10% of untreated latent infected individuals will develop TB disease [1]. The most important risk factor for developing TB disease is immunosuppression (e.g. HIV, cancers, poor nutrition, alcoholism, ageing) [1, 2, 3].

TB typically affects the lungs, although it may also affect other sites of the body (extrapulmonary TB) [2].

Pulmonary TB disease has a wide spectrum of clinical manifestations, which include chronic cough, low-grade fever, night sweats, fatigue, and weight loss [1]. Extrapulmonary forms of TB can affect any organ of the body, resulting in various clinical manifestations. Especially infants and young children are at risk of developing severe disseminated disease associated with a high mortality rate [2]. In high TB endemic areas WHO recommends BCG vaccination to all infants as a standard procedure [3].

Globally, 1.7 billion individuals are estimated to be infected with M. tuberculosis and without treatment 5-10% of these individuals will develop TB disease during their lifetime. Actually, more than 10 million individuals develop TB disease each year, and the disease is responsible for more than 1 million deaths [1, 2, 3].

For more details, please see WHO disease description for TB.