Meta-analysis on the Effect of Current Smoking on the Risk of Developing Community Acquired Pneumonia

Smoking impairs mucociliary clearance by causing reduction of ciliary beat frequency, increasing mucous production and number of abnormal cilia(1). Previous studies report a link between current smoking and community acquired pneumonia (CAP). We aimed to systematically review the literature to establish the effects of current smoking on the risk of developing CAP in adults. We systematically searched MEDLINE, EMBASE, CINAHL, LILACS and Web of Science to identify case-control studies, cohort studies and randomised controlled trials on the association of current smoking and CAP (defined by study authors as a clinical or radiological diagnosis of CAP in adults(2)). Pooled odds ratios (ORs) or hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated by using random effects model. Study quality was assessed by the Newcastle-Ottawa Scale. 647 studies were identified for title and abstract screening. Following screening by two independent reviewers, 58 studies met the inclusion criteria and were retrieved for full text review. 26 studies were eventually included for data extraction. The mean quality score across the studies included was 5.70 (SD 0.99). Current smokers were just over 2 times more likely to have CAP [OR 2.20 (95% CI 1.80, 2.68, 18 studies)]. The effect was smaller when looking at incidence of CAP in cohort studies [HR 1.47 (95% CI 1.19, 1.83, 8 studies)]. Similar to other respiratory diseases, smoking is an important risk factor for CAP. Reduction in smoking prevalence could result in significant decrease the clinical and economic burden of CAP.