Compilation of Harm: Tobacco, Chronic Obstructive Pulmonary Disease, and Mucus Plugs. Systematic Review of the Literature and Meta-Analysis.

Introduction: In COPD patients, mucus plugs are associated with lower lung function, worse quality of life, higher all-cause mortality, and a higher rate of exacerbations. The aim of the study was to determine whether subjects with COPD with a higher cumulative smoking history, such as current smokers, have a higher mucus plug score compared to former and never smokers with COPD. Material and methods: We have carried out a systematic review of the literature (SRL) and a meta-analysis (MA). Results: Nine articles were finally included in the SRL, and 6 of them were part of the MA. We found that subjects who had never smoked had a lower rate of mucus plugs when compared to active and ex-smokers (OR 0.08 [CI 95% 0.06, 0.12]). When comparing subjects with and without mucus plugs between current smokers vs. ex-smokers, we found that ex-smokers had a higher rate of mucus plugs than current smokers (OR 1.12 [CI 95% 1.02, 1.24]). When comparing subjects without mucus plugs or with a low mucus plug score (0-2) with a high mucus plug score (>3) between current smokers vs. ex-smokers, we found that ex-smokers had a higher mucus plug score than current smokers (OR 1.19 [CI 95% 1.08, 1.32]). Conclusions: We found that subjects who have never smoked have a lower rate of mucus plugs than those who have smoked and that ex-smokers with COPD have a higher rate of mucus plugs than current smokers with COPD. Quitting smoking is the most significant modifiable risk factor for COPD.