Low Prevalence of Latent Tuberculosis Infection among Contacts of Smear-Positive Adults in Brazil.

This follow-up cross-sectional study aimed to analyze the prevalence rate and risk factors related to latent tuberculosis infection (LTBI) and active tuberculosis (TB) in children aged < 15 years in contact with adults with smear-positive pulmonary TB (PTB) in a Brazilian municipality. Data were collected from interviews, clinical evaluations, chest X-rays, tuberculin skin tests, and interferon gamma release assays. The median time elapsed between diagnosis of the index case (IC) and inclusion in the study was 2.5 years (interquartile range [IQR] = 1.5-4.4) and 7.4 years (IQR = 3.8-9.7) when we reassessed the development (or not) of active TB. The median age at the time of exposure to the IC was 6.6 years (IQR = 3.3-9.4) and 14.1 years (IQR = 8.9-17.7) at the last follow-up. Of the 99 children and adolescents in contact with smear-positive PTB, 21.2% (95% CI = 14.0-29.9) were diagnosed with LTBI, and none developed active TB. There was no statistically significant difference between the LTBI and non-LTBI groups regarding demographic, socioeconomic, and epidemiological characteristics. Unlike national and international scenarios, we found a lower frequency of LTBI and no active TB among our studied patients. For better understanding of these findings, further studies might add, among other factors, host and genetic features.