Abstract
BACKGROUND: Smoking is known to increase the risk of tuberculosis (TB) infection, active TB disease, relapse following treatment and death from TB, but its significance is often underappreciated as a potentially reversible risk factor in public health and clinical TB practice in Canada. OBJECTIVE: To review the current evidence on smoking and the risk of TB, describe a cluster investigation of local TB transmission related to smoking in Toronto, Ontario, and discuss the practical implications of smoking for TB elimination in Canada. INVESTIGATION AND PUBLIC HEALTH RESPONSE: Three TB cases were identified at the same workplace over a two year period. All three strains matched on genotyping. Extensive interviews with the cases and workplace / building managers confirmed that the three cases did not work or socialize together. The only epidemiologic link identified was that all three were regular smokers and used the same location outside the building for smoke breaks. A building ventilation assessment confirmed that unfiltered air was not recirculated between floors. Based on the epidemiological and laboratory evidence, we determined that transmission likely occurred at the partly-sheltered smoking area outside of the worksite. We established and advertised an active case-finding clinic on-site to all workers who frequented smoking areas near the building. Of 60 individuals screened with tuberculin skin testing (TST), no additional active TB cases were identified. One Canadianborn person was found to be TST positive. We also offered TB education sessions to all staff in the building, and used the opportunity to promote smoking cessation for interested individuals. CONCLUSION: This cluster shows compelling evidence for smoking-related transmission of TB in Toronto. The World Health Organization has called for integration of anti-smoking efforts as a key strategy toward TB elimination. Opportunities to integrate smoking and TB work in Canada include assessment for smoking-related transmission during contact investigations, routine use of smoking cessation supports for contacts and others with latent tuberculosis infection as well as those with active TB, and public health outreach.