Associations Between Air Pollution and the Onset of Acute Exacerbations of COPD: A Time-Stratified Case-Crossover Study in China.

Background: Associations between air pollution and the acute exacerbations (AEs) of COPD have been established primarily in time-series studies in which exposure and health data were at the aggregate level, limiting the identification of susceptible populations.

Research question: Are air pollutants associated with the onset of AEs of COPD in China? Who is more susceptible to the effects of air pollutants?

Study design and methods: Data regarding AEs of COPD were obtained from the Acute Exacerbation of Chronic Obstructive Pulmonary Disease Registry (ACURE) study, and air pollution data were assigned to individuals based on their residential address. We adopted a time-stratified case-crossover study design combined with conditional logistic regression models to estimate the associations between six air pollutants and AEs of COPD. Stratified analyses were performed by individual characteristics, disease severity, COPD types, and the season of exacerbations.

Results: A total of 5,746 patients were included. At a 2-day lag, for each interquartile range increase in fine particulate matter and inhalable particulate matter concentrations, ORs for AEs of COPD were 1.054 (95% CI, 1.012-1.097) and 1.050 (95% CI, 1.009-1.092), respectively. The associations were more pronounced in participants who were younger than 65 years, who had experienced at least one severe AE of COPD in the past year, who had received a diagnosis of COPD between 20 and 50 years of age, and who had experienced AEs of COPD in the cool seasons. By contrast, significant associations for nitrogen dioxide, sulfur dioxide, and carbon monoxide lost significance when excluding patients collected before 2020 or with greater distance from the monitoring station, and no significant association was observed for ozone.

Interpretation: This study provides robust evidence that short-term exposure to fine particulate matter and inhalable particulate matter was associated with higher odds of AEs of COPD onset. Individuals who are young, have severe COPD, or whose first diagnosis of COPD was made when they were between 20 and 50 years of age and experience an exacerbation during the cooler seasons may be particularly susceptible.

Trial registry: ClinicalTrials.gov; No.: NCT2657525; URL: www.

Clinicaltrials: gov.