Association between outdoor PM and prevalence of COPD: a systematic review and meta-analysis.

There were conflictions and differences among the results of cross-sectional studies association between PM and COPD prevalence. We aimed to explore the real association between outdoor PM and COPD prevalence, analyze the possible cause to the differences and conflictions in previous cross-sectional studies. Cross-sectional literatures about the association between outdoor PM and COPD prevalence were selected up to 12 September 2018. Subgroup analysis was performed to explore the source of the heterogeneity. Publication bias was tested via funnel plot. Leave-one-out method was used to conduct influential analysis. Variance analysis was used to analyze the influence of concentration, literature quality and age (over 60 or not) on the ln (aOR) values. The initial search revealed 230 studies, of which 8 were selected. The heterogeneity in this study was significant (I=62, P<0.01), and random effects model was used. The pooled OR for the association between PM and COPD prevalence is 2.32(95%CI, 1.91-2.82). There was no evidence of publication bias. Subgroup analysis showed the subgroup of age seemed to be the source of heterogeneity (P=0.0143, residual I=0%). Variance analysis showed that the differences of ln (aOR) among each concentration group(p=0.0075) were statistically significant, the same as age groups(P=0.0234). This meta-analysis study demonstrated a conclusive association between PM and prevalence of COPD (OR: 2.32, 95%CI 1.91-2.82). The significant heterogeneity among selected studies was mainly caused by age (over 60 or not). High PM concentration should be needed in further research of the relationship between PM and chronic diseases.