Methods: To address the health effect of diurnal variation of traffic-related air pollutants on asthma-related emergency department (ED) visits, we applied generalized linear model with over dispersed poison distribution to daily asthma-related ED visits between 2008 and 2011 in Seoul, Korea. The indicator variable of diurnal variation of traffic-related air pollutant, the diurnal range of NO2 (drNO2) was adopted and defined as the difference level of NO2 between 10:00 and 05:00 in the morning. The statistical analysis was conducted to estimate the effect of drNO2 adjusted for temperature, relative humidity, air pressure, PM10, O3, influenza epidemic indicator, day of week, and time trend. Age-specific effects and seasonality were tested and the age-specific groups were defined as the middle-aged aged between 50 and 74 and the elderly aged above 75.
Results: Among the total 19,702 asthma-related ED visits during study period, 6,933 were recruited with the middle-aged 4,503, and the elderly 2,430 and the increased overall risk were suggested with relative risk percent change with 95% confidence interval (95% CI); middle-aged [2.1 (95% CI; -11.3, 17.6)], and the elderly [23.6 (95% CI; 3.1, 48.3)] at lag0-8 by 1 interquartile range (IQR) increase of drNO2. Season specific effect for the middle-aged were [-12.4, (95% CI; -31.3, 11.6)], [8.3, (95% CI; -16.8, 40.8)], [-9.3, (95% CI; -34.2, 25.1)], and [28.4, (95% CI; -3.9, 71.6)] and the elderly were [23.0, (95% CI; -9.1, 66.5)], [20.2, (95% CI; -15.0, 70.0)], [-1.9, (95% CI; -36.0, 50.3)], and [52.5.0, (95% CI; 3.8.1, 123.9)] at lag0-8 for spring (March- May), summer (June- August), fall (September- November), and winter (December- February) respectively. Among the middle-aged group, the estimated effect during winter were detected at lag0-4 [24.6, (95% CI; 2.3, 51.6)], lag0-5 [32.1, (95% CI; 5.7, 65.2)], lag0-6 [31.2, (95% CI; 2.2, 68.4)], and lag0-7 [32.8, (95% CI; 1.4, 73.9)] during winter. This study suggests an adverse relationship between ambient drNO2 with the risk of asthma-related ED visits and the level of drNO2 was related to asthma exacerbations especially during spring and winter period and the delayed effect were varied by age-groups.
Conclusion: This provides evidence that heavily increased levels of traffic-related pollutant are associated with poorly controlled asthma among the adults during cold period.