The Role of Youths in Within-Household Tuberculosis Transmission: A Household Contact Cohort Study.

BACKGROUND: Youth aged 15-24 years are significantly impacted by tuberculosis globally. Their expanding social networks heighten exposure risks, potentially amplifying tuberculosis transmission, but their role in within-household transmission remains poorly understood.

METHODS: A household contact cohort study in Lima, Peru (2009-2012) enrolled individuals (>15 years) with incident tuberculosis (index patients) and their household contacts (HHCs), following them for 12 months. We evaluated whether the age of index patients and HHCs modified the risk of tuberculosis infection among HHCs. Study outcomes included: (1) prevalent tuberculosis infection among child contacts (<15 years) at enrollment and (2) incident tuberculosis infection among HHCs. Whole-genome sequencing of Mycobacterium tuberculosis (Mtb) isolates from index-HHC pairs assessed whether index patient age modified the likelihood of within-household transmission, defined as &#x2264;12 single-nucleotide polymorphism differences.

RESULTS: Child contacts of youth index patients had a lower risk of prevalent tuberculosis infection than those with adult index patients (aRR = 0.77; 95% CI: .67-.87). Among index-secondary patient pairs, 62% (26/42) of pairs with a youth index patient were genetically linked, compared to 72% (48/67) of pairs with an adult index patient (P = .3). Child and youth contacts had lower incident tuberculosis infection risk at 12-month follow-up compared to adult contacts (child vs adult: HR = 0.33; 95% CI: .28-.38; youth vs adult: HR = 0.61; 95% CI: .52-.71).

CONCLUSIONS: Youth play a limited role in household tuberculosis transmission. Compared to adults, youth transmitted less TB as index patients and were less likely to be infected as HHCs. Research should explore youth social interactions and community-based transmission to inform targeted prevention strategies.