Emergency Department Visits for Asthma Exacerbation due to Weather Conditions and Air Pollution in Chuncheon, Korea: A Case-Crossover Analysis

PURPOSE This retrospective study was conducted to estimate the effects of climate factors and air pollution on asthma exacerbations using a case-crossover analysis. METHODS Patients who visited the emergency department (ED) of 2 university hospitals in Chuncheon for asthma exacerbations from January 1, 2006, to December 31, 2011, were enrolled. Daily average data for meteorological factors (temperature, daily temperature range, relative humidity, wind speed, atmospheric pressure, presence of rain, solar irradiation, and presence of fog) and the daily average levels of gaseous air pollutants (SO₂, NO₂, O₃, CO, and PM10) were obtained. A case-crossover analysis was performed using variables about the weather and air pollution at 1-week intervals between cases and controls before and after ED visits. RESULTS There were 660 ED visits by 583 patients with asthma exacerbations. Low relative humidity (lag 1 and 2) and high wind speed (lag 1, 2, and 3) were associated with ED visits for asthma. Fog (lag 2) showed protective effects against asthma exacerbations in Chuncheon (risk increase: -29.4% [95% CI=-46.3% to -7.2%], P=0.013). These relationships were stronger in patients ≤19 years old than in those >60 years old. High levels of ambient CO (lag 1, 2, and 3) and NO₂ (lag 2 and 3) were associated with decreased ED visits for asthma. However, there were no significant relationships among levels of ambient CO or NO₂ and asthma exacerbations after adjusting for wind speed and relative humidity. CONCLUSIONS High wind speed and low humidity were associated with an increased risk of asthma ED visits. Fog was associated with a decreased risk of asthma ED visits after controlling for seasonal variations in weather and air pollution.