Relationship Between Particulate Matter (PM_2.5) and Hospitalizations and Mortality of Chronic Obstructive Pulmonary Disease Patients: A Meta-Analysis

Background: Numerous studies have reported associations between particulate matter with aerodynamic diameters of ≤2.5 μm (PM_2.5) and chronic obstructive pulmonary disease (COPD) hospitalizations and mortality in cities worldwide. Nonetheless, the evidence of an association remains varied and limited. Methods: Systematic searches were conducted in 6 common English and Chinese electronic databases (i.e., PubMed, Web of Science, EMBASE, Ovid, Google Scholar, and China National Knowledge Infrastructure [CNKI]). A meta-analysis was performed to estimate the odds ratio (OR) to evaluate the relationship between PM_2.5 and COPD hospitalizations and mortality. Publication bias and heterogeneity of samples were tested using a funnel plot and the Egger's test. Studies were analyzed using either a random-effect model or a fixed-effect model. Results: The search yielded 18 studies suitable for meta-analysis during the period from Jan 1, 2010 to Dec 31, 2018. A 10-μg/m³ increase in PM_2.5 was associated with a 2.5% (95% confidence interval [CI]: 1.8-3.2%) increase in COPD hospitalizations, with an OR of 1.025 (95% CI: 1.018-1.032), and a 1.5% (95% CI: 0.9-2.2%) increase in COPD mortality, with an OR of 1.015 (95% CI: 1.009-1.022). Comparing different age groups, elderly people were more sensitive to the adverse effects. The estimated risk was higher in European countries than Asian countries, and in warm compared cold seasons. Various additional confounding factors also led to different results. Conclusions: PM_2.5 is associated with COPD hospitalizations and mortality. Controlling ambient air pollution would provide benefits to COPD patients.