BACKGROUND: Despite the evident age differences in the risk of asthma attack due to air pollution, most studies have recruited subjects from all age groups. Although this effort might be feasible for maintaining statistical power, it biases the effect estimate towards the null among children who are more sensitive to air pollution than adults. OBJECTIVES: To estimate the risk of air pollution on children living in Seoul who have made doctor visits for asthma. METHOD: From 1992 to 1993, daily number of doctor visits due to asthma attack was tallied among children between 4 and 11 years old living in Seoul from the insurance claim forms of Korean Medical Insurance Corporation (KMIC). 24-hour mean concentrations were calculated for TSP, SO2, O3 and NO2 based on hourly concentrations measured at 20 monitoring stations. To estimate the effect of TSP or SO2 on asthma attack, a Poisson regression model was used with adjustments for long-term trend, seasonal variation, day-of-week effect, and meteorological factors such as temperature, humidity, wind velocity and duration of sunshine. To prevent autocorrelation, autoregressive error terms were tried with different lag periods. RESULTS: The cumulative effect of a current day and previous five days turned out to be stronger than that of any single day. These relationships were observed more clearly after the effects of O3 and NO2 were controlled. For 100microgram/m3 increase of cumulative concentration of TSP, the relative risk was 1.27 (95% CI: 1.08, 1.49); for 50ppb increase of cumulative concentration of SO2, the relative risk was 1.56 (95% CI: 1.29, 1.89). After the effects of O3 and NO2 were removed in a multiple regression model, it increased to 1.37 (95% CI: 1.10, 1.69) and 1.66 ((%% CI: 1.34, 2.07), respectively. CONCLUSION: The concentrations of TSP and SO2 turned out to be significantly associatedwith asthma attack among children. As expected, the risk estimates were larger than those of previous studies which recruited subjects from all age groups, or used mortality or hospitalization as their outcome.
Adult ; Air Pollution* ; Asthma* ; Bias (Epidemiology) ; Child ; Hospitalization ; Humans ; Humidity ; Insurance ; Meteorological Concepts ; Mortality ; Seasons ; Seoul* ; Sunlight ; Wind