Transmission of Mycobacterium tuberculosis in Child and Adolescent Contacts in Brazil

Overview

This multi-center prospective cohort study in Brazil evaluated Mycobacterium tuberculosis infection (TBI) among children and adolescents exposed to pulmonary TB cases. Using IGRA testing, the study identified risk factors associated with transmission in close contacts, highlighting the vulnerability of younger age groups and the importance of household exposure.

Background

Tuberculosis remains a major global health issue, with nearly a quarter of the world population infected with Mycobacterium tuberculosis. Children and adolescents are particularly vulnerable, accounting for 16% of active TB cases globally in 2024, with young children under 5 at highest risk for severe disease. In Brazil, TB continues to significantly affect children and adolescents, with increasing cases in those under 5 years. Household exposure to infectious TB cases is a key driver of transmission, but only a subset of exposed children become infected, suggesting additional factors influence transmission risk.

Data Highlights

The study enrolled close contacts of culture-positive pulmonary TB cases from five sites across three Brazilian states between 2015 and 2019. Close contacts were defined as individuals with ≥4 hours/week exposure to the index case in the prior 6 months. IGRA testing was performed at baseline and repeated at 6 months if initially negative. TB preventive treatment was recommended for contacts with positive IGRA, those ≤5 years old, or HIV-infected. The cohort included children and adolescents stratified into age groups: <5, 5–9, 10–14, and 15–18 years.

Key Findings

• Children and adolescents exposed to pulmonary TB cases had a significant prevalence of TBI as determined by IGRA positivity.
• Household exposure increased the risk of TBI nearly fourfold compared to community controls without known exposure.
• Not all close contacts became infected, indicating host, environmental, or pathogen-related factors influence transmission.
• IGRA testing provided a standardized and specific method for detecting TBI, with advantages over TST, especially in BCG-vaccinated populations.
• TB preventive treatment was implemented according to Brazilian guidelines, targeting high-risk groups including young children and IGRA-positive contacts.

Clinical Implications

Clinicians should prioritize screening and preventive treatment for children and adolescents with close household exposure to pulmonary TB, especially those under 5 years of age. IGRA testing offers a reliable tool for identifying latent infection in this population, facilitating timely intervention. Understanding that not all exposed contacts become infected underscores the need for comprehensive risk assessment including host and environmental factors.

Conclusion

This study reinforces the critical role of household exposure in Mtb transmission among children and adolescents in Brazil and supports the use of IGRA for detecting latent infection. Targeted preventive strategies in high-risk pediatric contacts are essential to reduce TB burden in endemic settings.

References

1. World Health Organization 2023 -- Global Tuberculosis Report
2. Brazil Ministry of Health 2023 -- National TB Surveillance Data
3. RePORT Brazil Consortium 2015-2019 -- Prospective Cohort Study Protocol
4. Brazilian National TB Guidelines 2023 -- Diagnosis and Treatment