Background: Children who are contacts of individuals with active pulmonary tuberculosis (PTB) are at risk of acquiring Mycobacterium tuberculosis infection (TBI). We evaluated the determinants of TBI in child and adolescent contacts.

Methods: Pediatric (≤ 18 years old) close contacts of PTB patients enrolled in a multi-center Brazilian observational cohort were followed up to 6 months. Clinical evaluation, radiographic examination, and interferon gamma release assay (IGRA) were performed. Positive IGRA result at baseline or month 6 (IGRA-conversion) was considered an indicator of TBI. Multivariable mixed-effects logistic regressions were performed to identify factors associated with TBI.

Results: Among 562 close contacts enrolled, 171 (30.4%) had a positive IGRA at baseline, and 37 (9.5%) converted at month 6. Positive AFB, persistent cough and cavity on chest X-ray of TB index were independently associated with a positive IGRA result at baseline. IGRA-conversion was independently associated with older age among contacts and chest X-ray cavitations in the index cases. Contacts ≥ 15.9 years old had 3.4 (95%CI: 1.49–7.78, p = 0.004) adjusted odds ratio of IGRA-conversion than those < 15.9 years old.

Conclusion: Among pediatric close TB contacts, the prevalence of IGRA positivity increased with age. Older children have substantially higher susceptibility to TBI upon exposure.