People who smoked tobacco were 1.57 times more likely to develop tuberculosis when compared to those who had never smoked (pooled relative risk ratio 1.57, 95% confidence interval 1.18 to 2.10). Click here to see a forest plot of the findings – Figure A.
To explore the impact of the methodological quality of the four studies included in the review, the analysis was grouped into higher (≥7) versus lower (<7) quality studies according to the Newcastle-Ottawa scale score. Significant differences were seen between the two subgroups (p<0.00001), as only a significant increase in risk of tuberculosis was seen in the three studies with a higher quality. Click here to see a forest plot of the findings – Figure B.
Number of cigarettes
All of the studies reported an increased risk of tuberculosis with increasing numbers of cigarettes smoked per day (Leung 2004; Pednekar 2007; Lin 2009; Jee 2009). Also, data from one study showed a significant trend in the increased risk of tuberculosis with increasing pack-years of smoking (Lin 2009).
The two studies that investigated passive smoking showed that people who are exposed to household tobacco smoke were 1.44 times more likely to develop tuberculosis when compared to people who were unexposed to tobacco smoke (pooled relative risk ratio 1.44, 95% confidence interval 1.02 to 2.04). Click here to see a forest plot of the findings – Figure C.
Both of the included studies were deemed to be of high quality (≥7), and similar results were seen for the study which solely recruited females (Leung 2010) when compared to the study which recruited males and females (Lin 2009).
No significant trend was seen between the increased frequency of exposure to passive smoke (numbers of days per week exposed) and the risk of tuberculosis (p=0.74) (Lin 2009).