Household Smoking Patterns and Caregiver–Index Relationship Modify Mycobacterium tuberculosis Infection and Tuberculosis Risk in Children

Background: Young children are especially vulnerable to Mycobacterium tuberculosis infection and disease, with household exposure to cigarette smoke elevating this risk. Children's relationship to tuberculosis index patients and smokers may modify dual-exposure intensity but is poorly understood. We examined associations between household smoker index and caregiver status, and M tuberculosis infection and disease in South African child contacts.

Methods: This secondary analysis of an observational cohort study conducted in Cape Town, South Africa (2008–2012) included 741 children aged 3 months–15 years living with an adult who started tuberculosis treatment in the preceding 3 months. Tuberculosis infection and disease were assessed by tuberculin skin test, clinical, radiological and microbiological evaluation. Informed by a Directed Acyclic Graph, random effects logistic regression controlled for ethnicity, child age, child–index contact time, and household clustering.

Results: The adjusted odds of child M tuberculosis infection were 2·1(0·9-5·2) with index but not caregiver smoking, 1·9(1·0-3·8) with caregiver but not index smoking, 3·6(1·5-8·8) with both caregiver and index smoking, and 6·6(2·6-16·8) if the index was the caregiver and smoked, compared to households where neither smoke. Child contacts had four-fold higher odds of tuberculosis (aOR 4·2(1·4-12·5)) if the caregiver was the index patient and smoked.

Interpretation: Concurrent household index patient and caregiver smoking increased children’s odds of M tuberculosis infection and disease. Routine household-wide smoking cessation could reduce children’s future vulnerability to tuberculosis.