Short-term effects of multiple outdoor environmental factors on risk of asthma exacerbations: age-stratified time-series analysis

Abstract Background Although the different age groups had differences in sensitivity of asthma exacerbations (AEs) to the environmental factors, no comprehensive study has examined the age-stratified effects of environmental factors on AEs. Objective To examine the short-term effects of age-stratified groups (infants, preschool children, school-aged children, adults, and elderly) of outdoor environmental factors (air pollutants, weather conditions, aeroallergens, and respiratory viral epidemics) on asthma exacerbations. Methods We performed an age-stratified analysis of the short-term effects of four groups of outdoor environmental factors on AEs in Seoul Metropolitan City (Korea) from 2008 and 2012. The statistical analysis employed a Poisson generalized linear regression model, with a distributed lag non-linear model for identification of lagged and non-linear effects and convergent cross mapping for identification of causal associations. Results Analysis of the total population (n=10,233,519) indicated there were 28,824 AE events requiring admission to an emergency department during the study period. Diurnal temperature range had significant effects in pediatric (infants, preschool children, and school-aged children) and elderly people (RR: 1.056-1.078 and 1.016, respectively). Tree and weed pollen, human rhinovirus, and influenza virus had significant effects in school-age children (RR: 1.014, 1.040, 1.042, and 1.038, respectively). Tree pollen and influenza virus had significant effects in adults (RR: 1.026 and 1.044, respectively). Outdoor air pollutants (PM10, NO2, O3, CO, and SO2) had significant short-term effects in all age groups (except for CO and SO2 in infants). Conclusion These findings provide the need for the development of tailored strategies to prevent asthma exacerbation events in different age groups.