Impact of immigration on tuberculosis infection among Canadian-born schoolchildren and young adults in Montreal

We conducted a cross-sectional tuberculin survey among non-BCG-vaccinated Canadian-born schoolchildren in grades 6 and 10, health professional students, and young adult workers, to estimate the association of tuberculin reactions with indices of contact with tuberculosis. Participants underwent simultaneous tuberculin testing with PPD-T (standard) and PPD-B (from M. intracellulare). Exposure was estimated from questionnaire responses, group, aggregate census, and tuberculosis incidence data. Of 3,710 participants, 88 (2.4%) had positive tuberculin reactions, i.e., of 10+ mm. Positive tuberculin reactions were rarely associated with larger reactions to PPD-B, but were associated with older age (adjusted odds ratio for each 5 years: 1.5 [95% confidence interval, 1.3, 1.8]), household contact (4.2 [1.4, 12.7]), and population group (health professional versus all others: 0.6 [0.3, 1.0]). Estimated annual risk of infection declined by 3% per year. Tuberculin reactions were not associated with any indices of contact in school, work or neighborhood settings with foreign-born from tuberculosis endemic areas, nor with tuberculosis in Canadian-born. There was no evidence of transmission of tuberculosis from affected high risk sub-groups in Montreal to the general population working or attending school.