Methods : Case crossover design was used. This study is based on the national health insurance claim (ICD : J45, J46), air pollutants [PM10(㎍/㎥), CO(ppb), SO2(ppb), NO2(ppb), O3(ppb)] and climate [temperature(℃), humidity(%), visibility(km), wind speed(m/s), air pressure(hPa)] data from 2007 to 2013 in Seoul and Incheon, Korea. The socioeconomic status was classified into health insurance group and medical aid group. The daily maximum value of air pollutants and daily average climate were calculated. The daily numbers of asthma cases on the ‘Event’ days were compared with ‘Control’ days. To select event days, 2 criteria were applied: 1) exclude weekends 2) excluded reoccurred Asian dust events on the 14 days before and after the Asian dust event. It was observed for 7 days after the events days. Control days is defined as the 7 days before and after the event days. Log poisson regression was used to estimate the ratio of averaged asthma cases using age, gender, region and climate between event and control days.
Results: 7 event days were selected. On the event days, the average numbers of asthma cases were much more than the control days on the gender, age, region and socioeconomic status. However, there was no significant difference statistically. Humidity of the event days was lower (p=0.0950) but wind speed (p=0.0203) and PM10 (p=0.0376) were higher than control days. The estimated ratio of averaged asthma cases on event days was 0.96 (95% C.I.: 0.95-0.98). According to the socioeconomic status, the ratio of asthma patients during 7 days from ‘day +0’ to ‘day +6’ were as follows: 0.96 (0.95 - 0.97) on the day +0, 1.27 (1.26 - 1.29) on the day +1, 1.11 (1.09 - 1.13) on the day +2, 1.25 (1.23 - 1.26) on the day +3, 1.13 (1.12 - 1.15) on the day +4, 1.06 (1.04 - 1.07) on the day +5 and 0.83 (0.81 - 0.84) on the day +6 in the health insurance group. Also, in medical aids group, the estimated ratio of the each day were 1.00 (0.94 - 1.07), 1.14 (1.06 - 1.22), 1.15 (1.06 - 1.25), 1.18 (1.11 - 1.25), 1.08 (1.01 - 1.15), 1.02 (0.94 - 1.10) and 0.78 (0.74 - 0.83).
Conclusion: Asian dust events can worsen asthma and its effects on asthma appear differently by the socioeconomic status. Time lag analysis is needed in studying asthma effect on Asian dust event using claim data.