Effects of PM on mortality in pure COPD and asthma-COPD overlap: difference in exposure duration, gender, and smoking status.

We investigated the effects of particulate matter (PM) on mortality in patients diagnosed with asthma-COPD overlap (ACO) or 'pure COPD'. Subjects from the National Health Insurance Service-National Sample Cohort of Korea, who were aged 40 years or above and had newly diagnosed COPD since 2009 were selected. Finally, 6,313 patients were enrolled and divided into 'pure COPD' and ACO groups. Average PM exposure data were obtained using Kriging interpolation from 2001 to 2013. Hazard ratios(HR) were estimated using a time-varying Cox regression model. Exposure to PM for 1, 3, and 6 months was associated with an increase in non-accidental mortality in the entire COPD group, especially the ACO group. When a stratified analysis of 3-month exposure was performed by sex, the highest HR was found in women with ACO (HR = 1.153; 95% confidence intervals [CI]: 1.121, 1.185). A stratified analysis according to smoking status showed that ACO patients had the highest HR among never smokers (HR = 1.151; 95% CI; 1.124, 1.178). Average exposure to PM was associated with non-accidental mortality in patients with COPD, especially those diagnosed with ACO. In addition, the adverse effects of PM exposure are more severe in women and never-smokers.