Background: Previous case-control studies and a small number of cohort studies in high-risk populations have found an association between smoking and tuberculosis, but no cohort studies have been conducted in the general population on this to date.

Objectives: To investigate the association between smoking and tuberculosis in a cohort of a general population.

Methods: Passive case finding and household contact investigation of TB patients was routinely done in Pakistan.  Four districts with a high concentration of slums were selected as intervention areas; Lahore, Rawalpindi, Faisalabad and Islamabad. From July 2013-June 2015, contact investigation beyond household was conducted: all people staying within a radius of 50 metres (using Geographical Information System) from the household of smear positive TB patients were interviewed and screened for tuberculosis as part of other activities of project. Those with presumptive TB were investigated using smear microscopy and the Xpert MTB/RIF test was performed on smear negative patients. All the diagnosed TB patients were linked to TB treatment and care.

Results: A total of 783043 contacts were screened for tuberculosis, of whom 19815 (2.53%) were smokers. Smoking was common among men, in diabetic & teenage, elderly age population and in household contact of smear positive TB patients.  Smoking was associated with an increased risk of tuberculosis (odds ratio [OR], 2.43; 95% confidence interval, 2.27 – 2.60) in household contact of smear positive TB patients. The association was stronger among those greater than 45 years of age (OR, 11.09) than those between 25-44 years of age (OR, 5.83) and diabetic persons (OR,2.0).

Conclusions: Smoking was associated with a twofold increased risk of active tuberculosis in a cohort of general population.