title: Emergency Department Visits for Asthma Exacerbation due to Weather Conditions and Air Pollution in Chuncheon, Korea: A Case-Crossover Analysis.
abstract: OBJECTIVE
  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.
authors: Department of Allergy and Clinical Immunology, Kangwon National University School of Medicine, Chuncheon, Korea.|Department of Internal Medicine and Environmental Health Center, Kangwon National University Hospital, Chuncheon, Korea.
authors: Jae Woo
authors: JW
authors: Kwon
authors: Department of Environmental Science, Kangwon National University, Chuncheon, Korea.
authors: Young Ji
authors: YJ
authors: Han
authors: Department of Preventive Medicine, Kangwon National University Hospital, Chuncheon, Korea.
authors: Moo Kyung
authors: MK
authors: Oh
authors: Department of Internal Medicine, Chuncheon Sacred Heart Hospital, Hallym University College of Medicine, Chuncheon, Korea.
authors: Chang Youl
authors: CY
authors: Lee
authors: Department of Biostatistics, Graduate School of Public Health, Seoul National University, Seoul, Korea.
authors: Ja Yeun
authors: JY
authors: Kim
authors: Department of Biostatistics, Graduate School of Public Health, Seoul National University, Seoul, Korea.
authors: E Jin
authors: EJ
authors: Kim
authors: Department of Biostatistics, Graduate School of Public Health, Seoul National University, Seoul, Korea.
authors: Ho
authors: H
authors: Kim
authors: Department of Internal Medicine and Environmental Health Center, Kangwon National University Hospital, Chuncheon, Korea. wjkim47@gmail.com.
authors: Woo Jin
authors: WJ
authors: Kim
keywords: Asthma; air pollution; climate; fog