In countries with a low incidence of Tuberculosis (TB), the incidence remains higher among the immigrant population than among the autochthonous population beyond the first years after arrival in the host country. In addition, at a pediatric level, most cases are produced in immigrant children and the children of immigrants. This persistence of a greater incidence in the immigrant population might, in part, be explained by the increase in exposure to Mycobacterium tuberculosis during trips to their country of origin to visit friends and relatives (VFRs). The objectives of the study are to estimate the risk of latent infection by M. tuberculosis (LTBI)/TB in children VFRs and the factors associated with this risk. The investigators will also study the behavior of the diagnostic tests. This project will be carried out in collaboration with 21 primary health care centers and 5 hospitals in Catalonia.

A prospective study will be carried out. The study subjects are children under 15 years of age, which are children of immigrants and born or not in Spain, who travel to VFRs to countries with an elevated incidence of TB (> 40 cases/100,000 inhabitants). A sample size of 492 children was estimated. Children will be recruited during a programmed visit to a traveler health clinic or a primary care center, a questionnaire will be completed with sociodemographic, epidemiologic and clinical data and a tuberculin skin test (TST) will be performed and read at 48-72 hours. At 8-12 weeks after returning from the travel abroad the child will have a new visit in which a questionnaire will be completed with epidemiological and clinical data, an a TST and QFT-Plus test will be performed. The rate of incidence of LTBI will be estimated per individual/month and person/year per country visited and by age group.

Inclusion Criteria (all criteria must be met):

• Informed consent must be obtained from the parents of legal guardian.
• Less than 15 years of age.
• One or both of the parents is from a country with an elevated incidence of TB. A country is considered to have an elevated incidence of TB when this incidence is 3-fold higher than the incidence in Catalunya, that is approximately 40/100,000 inhabitants. Countries with official reports describing an incidence less than the value proposed but which have regions with > 40 cases /100,000 inhabitants are also included (Table and figure 1)
• The journey to the country of origin is made by at least one of the parents.
• The duration of the visit to the country of origin is of at least 21 days.

Exclusion Criteria:

• Previous TB or LTBI.
• Tourist visit to hotels and resorts with scarce contact with the autochthonous population.
• Primary or secondary immunodeficiency to treatment with corticosteroids, transplantation, treatment with anti-tumor necrosis factor, chronic renal insufficiency.
• Congenital cardiopathy.
• Cystic fibrosis of the pancreas and other congenital diseases of pulmonary origin.