The present review started in August 2013 and was designed to up-date previous systematic reviews relating to the increased risk of developing tuberculosis with active and passive smoking. Four systematic reviews were identified that included literature published in the period up to 2007. At the same time, an updated search for additional original studies was performed using 2006 as a starting date to present. From these searches, a total of five original studies were found that fulfilled the criteria for inclusion in the present study.
One study assessed the effects of active and passive tobacco smoking on the risk of developing tuberculosis, three studies only assessed the effect of active smoking, and the remaining study only assessed the effect of passive smoking. Two of the studies used the same population of participants; however, one paper assessed the effect of active smoking (Leung 2004) and the other assessed the effect of passive smoking (Leung 2010).
Two of the studies used the incidence of tuberculosis as the outcome, one study used death from tuberculosis as the outcome, and the remaining two studies used incidence and/or death from tuberculosis as the outcome.
None of the included studies were conducted in Europe; two studies were conducted in Hong Kong (using the same recruited population), one in Taiwan, one in India, and one in South Korea.
The quality of the five studies (as judged by the Newcastle-Ottawa scale score) ranged from 5 to 8. Three of the studies assessing the effect of active smoking on tuberculosis were deemed of high quality and both of the studies assessing the effect of passive smoking on tuberculosis were deemed of high quality (≥7).