Changes in the relationship between childhood asthma and ambient air pollution in Taiwan: Results from a nationwide survey repeated 5 years apart

Background Childhood asthma is a common disease whose prevalence is changing. Shift in environmental exposure was one of the plausible explanations. This study investigated changes in the association between childhood asthma and ambient air pollution occurring over time. Method A nationwide questionnaire survey concerning respiratory illness and symptoms was administered to Taiwanese elementary and middle school students in 2011 and repeatedly in 2016‐2017. During the study period, the concentrations of ambient air pollutants were obtained from the Environmental Protection Administration (EPA) monitoring stations. Generalized estimating equation models were applied to examine the association between air pollution in the past year and the risk of current asthma. Results A total of 6346 children from the 2011 survey and 11 585 children from the 2016‐2017 survey attended schools located within a 1‐km radius of Taiwan EPA monitoring stations. The prevalence of childhood current asthma (children with physician‐diagnosed asthma and persistent asthma symptoms in the past year) increased from 7.5% to 9.6% during this period. The level of exposure to particulate matter with an aerodynamic diameter of ≤2.5 μm (PM2.5) in the past year was found to be associated with current asthma both in the 2011 survey (odds ratio (OR): 1.90, 95% confidence interval (CI): 1.41‐2.57) and in the 2016‐2017 survey (OR: 1.24, 95% CI: 1.04‐1.48). Conclusion Improved air quality has reduced the effect of PM2.5 on childhood asthma, but air quality remains a health concern in Taiwan.