Traffic-Related Pollution Levels and Poorly Controlled Asthma in Adults

Background: Numerous epidemiological studies have shown adverse associations between increases in outdoor air pollution and health outcome. The majority of studies focused on daily concentrations of air pollutions and small-scale variation in daily averages and peak concentrations has not been able to characterize. We investigated the seasonal association between diurnal variation of traffic-related air pollution and the exacerbations of asthma symptoms among the middle-aged and the elderly in urban settings.

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.