Objective: To compare clinical, radiological and laboratory aspects of household contacts, aged 15 or younger, of patients presenting a positive culture for Mycobacterium tuberculosis. Methods: This was a cohort study comparing children and adolescents (≤ 15 years of age) who were household contacts of TB cases presenting positive sputum smear and positive culture results (exposed group, n = 100) or negative sputum smear and positive culture results (unexposed group, n = 55). All of the contacts were evaluated via the TB control program of a university hospital in the city of Vitória, Brazil, between July of 2003 and December of 2006. Results: Of the 155 minors evaluated, 87 (56.1%) were female and 68 (43.9%) were male. Of those 155, 28 (18%) were aged 5 or younger, 62 (40%) were aged 5-9, and 65 (42%) were aged 10-15. Symptoms of the disease were found in 17 (17%) of the 100 contacts in the exposed group and in 9 (16%) of the 55 in the unexposed group (p = 0.86). Chest X-rays showed alterations in 20 (21%) and 2 (4%) of the contacts in the exposed and unexposed groups, respectively (RR = 6.9; p = 0.004). In the exposed and unexposed groups, respectively, 35 (38%) and 10 (18%) of the contacts presented positive results on the tuberculin skin test (RR = 2.8; p = 0.01). Of the 100 contacts in the exposed group, 5 (5%) were diagnosed with TB, which was not diagnosed in any of those in the unexposed group (p = 0.08). Conclusions: Although no significant difference was found between the two groups regarding the incidence of TB, it is of note that there is a greater risk of becoming infected with M. tuberculosis if the bacterial load of the index case is high.

Keywords: Tuberculosis; Mycobacterium tuberculosis; Tuberculosis, pulmonary; Child; Adolescent.