title: Air quality and the frequency of emergency room visits for asthma.
abstract: BACKGROUND
  Atmospheric pollution has been proposed as one of the possible factors responsible for increases in asthma mortality and morbidity.
  
  
  OBJECTIVE
  We sought to examine whether we could demonstrate a relationship between emergency room visits for asthma and alterations in environmental conditions.
  
  
  METHODS
  Over a 1-year period, the frequency of emergency room visits for asthma in a large urban hospital were documented and compared to outdoor concentrations of SO2, NO2, and ozone in addition to two overall measures of air quality (air pollution index and air quality index).
  
  
  RESULTS
  A total of 854 emergency room visits were noted with the highest number of visits occurring in May and between September and December. Significant variations in the frequency of visits as well as environmental conditions could be seen on a daily basis. Despite comparisons of results on a daily, weekly, and monthly basis, no significant relationships could be found between any of the pollution indices and emergency room visits. Staggering visits by 1 and 7 days, however, revealed a relationship between emergency room visits and air pollution index and air quality index. An association between emergency room visits and NO2 and ozone was seen when visits were staggered by 7 but not by 1 day.
  
  
  CONCLUSIONS
  We conclude the fluctuations in overall air quality are associated with increased frequency of emergency room visits but only when data are lagged by a predefined period.
authors.affiliation: Asthmas Center, Toronto Hospital, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Kesten
authors.forename: J
authors.initials: J
authors.lastname: Szalai
authors.forename: B
authors.initials: B
authors.lastname: Dzyngel
mesh_terms: D000393:Air Pollutants; D001249:Asthma / Q000139:chemically induced / Q000503:physiopathology*; D002170:Canada; D004630:Emergencies; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D006801:Humans; D010126:Ozone / Q000009:adverse effects / Q000032:analysis; D010545:Peroxides / Q000009:adverse effects / Q000032:analysis
chemical_list: D000393:Air Pollutants; D010545:Peroxides; C048370:sodium peroxide; D010126:Ozone