Fine Particulate Matter and Mortality in Chronic Obstructive Pulmonary Disease with Multimorbidity

<b>Rationale:</b> Exposure to particulate matter with an aerodynamic diameter ≤2.5 μm (PM_2.5) is associated with respiratory dysfunction and increased risk of death. The U.S. Environmental Protection Agency has established regulatory standards for long-term exposure in the general population, but the risk for individuals with existing respiratory disease is unclear. <b>Objectives:</b> Estimate the association between long-term PM_2.5 exposure and mortality in individuals with chronic obstructive pulmonary disease (COPD), including the modifying effects of comorbidities at low levels of exposure. <b>Methods:</b> We performed a retrospective cohort analysis of all patients with a COPD diagnosis in the Veterans Health Administration between 2016 and 2019. Annual ambient concentrations of PM_2.5 were obtained from publicly available pollutant models and spatially assigned to patient households. Primary outcomes were adjusted odds of mortality per 1-μg/m³ increase in 5-year PM_2.5 concentrations and identification of comorbidities associated with increased susceptibility. <b>Results:</b> Medical records from 1,124,973 veterans with COPD were analyzed. Most of the cohort were male (95.60%), and the cohort had diverse racial, socioeconomic, and geographic characteristics. The odds of death was 3.8% higher for every 1-μg/m³ increase in long-term PM_2.5 (adjusted odds ratio [aOR], 1.038; 95% confidence interval [CI], 1.035-1.040). For people with comorbid lung cancer (aOR, 1.051; 95% CI, 1.035-1.068), coronary arterial disease (aOR, 1.039; 95% CI, 1.033, 1.044), or chronic kidney disease (aOR, 1.042; 95% CI, 1.034, 1.049), the risk of death was significantly higher than for those without. <b>Conclusions:</b> The risk of mortality increases at even small magnitudes of increased PM_2.5 concentrations in people with COPD. The risk was higher for those with comorbid lung cancer, coronary artery disease, and chronic kidney disease. The current standard of 9 μg/m³ for the general population should be reevaluated for those with existing COPD.