Worldwide tuberculosis (TB) is still a very prevalent disease. That is also the case of Brazil. People with latent TB represent an important obstacle to control tuberculosis because they function as reservoirs of M. tuberculosis and they can progress to disease early after infection or reactivate it in the future. The tuberculin skin test (TST) suggests previous contact with M. tuberculosis. The Brazilian Thoracic Association guidelines establish that an evidence of TB infection is an induration of TST equal to or larger than 10 mm for individuals vaccinated with BCG in the previous two years and equal to or larger than 5 mm for those vaccinated with BCG for more than two years. However, there is no data in literature to prove the best cut off for TST in infants. Thus, this study aims to determine the average induration after conducting TST in healthy infants. Infants aged between 8 and 18 months with BCG vaccine administered during the first month of life will be selected. They should have no prior contact with adults who cough for more than 3 weeks or who were diagnosed with tuberculosis. Also, they should not have been exposed to human immunodeficiency virus (HIV) or have evidence of known immunodeficiency. A pilot study with 15 children will define the number of children required for the project. The results from this study may confirm the cut off of 10 mm suggested by the Brazilian Thoracic Association for this age group and thus help to establish parameters of the absence of latent tuberculosis infection in children less than 2 years.
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