TB infection (previously called latent TB infection) is defined as a “state of persistent immune response to stimulation by M. tuberculosis antigens without evidence of TB disease” (15). The number of people worldwide estimated to have M. tuberculosis infection is 1.7 billion. Further, 7.5 million children aged under 15 years are estimated to be infected with TB every year (11). By 2014, a cumulative 67 million children aged under 15 years were infected with TB, including 2 million with MDR-TB and 100 000 with XDR-TB strains (12). People with TB infection have no signs or symptoms of TB disease and are not infectious, although they are at risk of developing TB disease in the future.
On average, 5–10% of people with TB infection develop TB disease over the course of their lives, usually within the first 5 years after initial infection. The risk for TB disease after infection is particularly increased among young children and in people with immunocompromising conditions such as HIV infection, in whom disease progression is also more rapid, usually within 12 months of infection.
Providing treatment for TB infection to prevent TB disease is a critical component of Pillar 1 of the WHO End TB Strategy (7). The efficacy of currently available TPT regimens ranges from 60% to 90% (28). The potential benefit of TPT needs to be balanced against the risk for drug-related adverse events. For people with TB infection in population groups with a high risk for progression to TB disease, the benefits of TPT are greater than the potential harms. Provision of TPT involves a comprehensive package of interventions: identification and testing in populations with high TB risk (including contacts of people with TB), delivering effective and safe preventive treatment, and monitoring and evaluation of the cascade of care (15).