Association Between Air Pollutants and Acute Exacerbation of Chronic Obstructive Pulmonary Disease: A Time Stratified Case-Crossover Design With a Distributed Lag Nonlinear Model.

Acute exacerbation of chronic obstruction pulmonary disease (AECOPD) as a respiratory disease, is considered to be related to air pollution by more and more studies. However, the evidence on how air pollution affect the incidence of AECOPD and whether there are population differences is still insufficient. Therefore, we select PM, PM, SO, NO, CO, and O as representatives combined with daily AECOPD admission data from 1 January 2015 to 26 June 2016 in the rural areas of Qingyang, northwestern China to explore the associations of air pollution with AECOPD. Based on a time-stratified case-crossover design, we constructed a distributed lag nonlinear model to qualify the single and cumulative lagged effects of air pollution on AECOPD. Stratified related risks by sex and age were also reported. The cumulative exposure-response curves were approximately linear for PM, "V"-shaped for PM, "U"-shaped for NO and inverted-"V" for SO, CO and O. Exposure to high-PM (42 μg/m), high-PM (91 μg/m), high-SO (58 μg/m), low-NO (12 μg/m), and high-CO (1.55 mg/m) increased the risk of AECOPD. Females aged 15-64 were more susceptible under extreme concentrations of PM, SO, CO, and low-PM than other subgroups. In addition, adults aged 15-64 were more sensitive to extreme concentrations of NO compared with the elderly ≥65 years old, while the latter were more sensitive to high-PM. High-SO, high-NO, and extreme concentrations of PM had the greatest effects on the day of exposure, while low-SO and low-CO had lagged effects on AECOPD. Precautionary measures should be taken with a focus on vulnerable subgroups, to control hospitalization for AECOPD associated with air pollutants.