The Role of Youths in Within-Household Tuberculosis Transmission

Who

• Participants:

  • Index patients: 2,771 individuals aged 15–60 years with microbiologically confirmed pulmonary TB.

  • Household contacts (HHCs): 10,745 contacts aged 0–60 years (participants >60 excluded).

• Key subgroups:

  • Index patients categorized as Youth (15–24 years) or Adults (25–60 years).

  • HHCs categorized as Children (0–14 years), Youth (15–24 years), and Adults (25–60 years).

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What

• Main findings:

  • Child household contacts exposed to youth index patients had a lower prevalence of TB infection at enrollment compared with those exposed to adult index patients (adjusted PRR = 0.77; 95% CI: 0.67–0.87).

  • Index patient age was not associated with the incidence of TB infection among household contacts over 12 months.

  • Children and youth contacts had significantly lower incidence of TB infection than adult contacts, regardless of index patient age.

  • Whole-genome sequencing (WGS) showed a lower proportion of genetically linked transmission pairs for youth index patients compared with adults, though this difference was not statistically significant.

• Interpretation:

  • Youths appear to contribute less to within-household TB transmission than adults, suggesting that their transmission risk may occur more often outside the household.

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When

• Study period: September 2009 to August 2012.

• Follow-up duration: 12 months after household enrollment.

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Where

• Setting: Lima, Peru.

• Healthcare context: 106 public health centers serving approximately 3 million people.

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Why

• To determine whether the age of TB index patients, particularly youth (15–24 years), influences the risk of TB transmission to household contacts, with a focus on children as a marker of recent transmission.

• To address gaps in understanding age-specific transmission dynamics and inform targeted TB control strategies.

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How

• Study design: Prospective household cohort study.

• TB infection assessment:

  • Baseline tuberculin skin test (TST) to measure prevalence.

  • Repeat TSTs at 6 and 12 months to measure incidence.

• TB disease classification:

  • Co-prevalent TB (≤14 days after enrollment) vs secondary TB (>14 days).

• Transmission confirmation:

  • Whole-genome sequencing of Mycobacterium tuberculosis isolates to assess genetic linkage between index and secondary cases.

• Analysis:

• Multivariable regression and survival analyses adjusting for demographic, behavioral, socioeconomic, and nutritional factors.

Source: Brooks, M.B., Lecca, L., Becerra, M.C., Calderon, R.I., Contreras, C.C., Jimenez, J., Yataco, R.M., Zhang, Z., Murray, M.B. and Huang, C.C., 2025. The Role of Youths in Within-Household Tuberculosis Transmission: A Household Contact Cohort Study. Clinical Infectious Diseases, p.ciaf490.