One third of the world?s population is estimated to have latent TB infection (LTBI); in other words, they do not have active TB disease but may develop it through a process of reactivation of dormant bacilli that start multiplying and produce active TB. The lifetime risk of reactivation for a person with documented Latent TB  Infection is estimated to be 5-10%, with the majority developing TB disease within 18 months of initial infection. This includes preventing people with latent TB from developing active, and infectious, TB disease. TB drug treatment for the prevention of TB, also known as chemoprophylaxis, can reduce the risk of a first episode of active TB occurring in people with latent TB.  
Preventive therapy requires the identification of at-risk populations for LTBI: adults and adolescents living with HIV, with unknown or a positive tuberculin skin test and are unlikely to have active TB should receive preventive treatment of TB. Infants aged < 12 months living with HIV who are in contact with a case of TB and are investigated for TB should receive 6 months of isoniazid preventive treatment (IPT) if the investigation shows no TB disease. Children aged