Effect of smoking on tuberculosis treatment outcomes: A systematic review and meta-analysis

<b>Introduction:</b> Numerous studies have explored the effect of cigarette smoking on tuberculosis treatment outcomes but with dissimilar conclusions. <b>Objective:</b> To determine the effect of cigarette smoking on tuberculosis treatment outcomes. <b>Methods:</b> PubMed, Cochrane library, and Google scholar databases were searched last on February 27, 2019. We applied the random-effects model for the analysis. Publication bias was assessed using funnel plot and Egger’s regression. Furthermore, we performed Orwin’s Fail-Safe N and cumulative meta-analysis to check for small studies’ effect. <b>Results:</b> Out of 22 studies we included in the qualitative synthesis, 12 studies reported p-values less than 0.05 where smoking significantly favored poor treatment outcomes. The remaining 10 studies reported p-values larger than 0.05 implying that smoking does not affect the treatment outcomes. The meta-analysis found that smoking significantly increased the likelihood of poor tuberculosis treatment outcomes by 51% (OR = 1.51; 95% CI = 1.30 to 1.75 and I-square = 75.1%). In a subgroup analysis, the effect was higher for low- and middle-income countries (OR = 1.74; 95% CI = 1.31 to 2.30) and upper-middle-income economies (OR = 1.52; 95% CI = 1.16 to 1.98) than for high-income ones (OR = 1.34; 95% CI = 1.03 to 1.75). Meta-regression analysis, adjusted for income, found the effect of smoking has not significantly improved over the years (p = 0.92) and thus implying neither of the covariates was the source of the heterogeneity. Egger’s regression test indicated that publication bias is unlikely (p = 0.403). <b>Conclusion:</b> Cigarette smoking is significantly linked with poor tuberculosis treatment outcomes.