title: The role of symptomatic colds in asthma exacerbations: Influence of outdoor allergens and air pollutants.
abstract: BACKGROUND
  Both air pollutants and respiratory viral infections have been recognized to be important triggers of asthma exacerbations, but the possible interaction of these has not been assessed in an epidemiologic study.
  
  
  OBJECTIVE
  In this study, we aimed to assess the possible associations of symptomatic colds with outdoor allergens and air pollutants in exacerbating asthma.
  
  
  METHODS
  A total of 57 adults and children with asthma participated in a 1-year study in Vancouver, British Columbia. Diary cards recording symptoms of asthma and colds, medication usage, and peak expiratory flow rates were completed twice daily. Outdoor air pollutant levels and levels of pollen and fungal spores were measured. Levels were examined for associations with exacerbations of asthma with symptoms of a cold, as compared with asthma exacerbations with no cold symptoms and colds in the absence of asthma exacerbations.
  
  
  RESULTS
  Of 130 asthma exacerbations, 47% were associated with cold symptoms (accounting for 44% of episodes of colds). Asthma exacerbations with colds were associated with higher levels of sulfur dioxide, and nitric oxide during March to November in comparison with asthma exacerbations without cold symptoms (P <.018). Cold-symptom days overall were more common in winter and were significantly associated with lower temperatures, lower ozone levels, and higher sulfur dioxide, nitrogen dioxide, nitrogen oxide (NO and NO(x)), and carbon monoxide levels.
  
  
  CONCLUSIONS
  Asthma exacerbations are commonly associated with cold symptoms. These episodes are associated with higher levels of sulfur dioxide and nitrogen oxides from March to November in comparison with asthma exacerbations without cold symptoms.
authors.affiliation: Department of Medicine and Public Health Sciences, University of Toronto, Ontario, Canada.
authors.forename: S M
authors.initials: SM
authors.lastname: Tarlo
authors.forename: I
authors.initials: I
authors.lastname: Broder
authors.forename: P
authors.initials: P
authors.lastname: Corey
authors.forename: M
authors.initials: M
authors.lastname: Chan-Yeung
authors.forename: A
authors.initials: A
authors.lastname: Ferguson
authors.forename: A
authors.initials: A
authors.lastname: Becker
authors.forename: C
authors.initials: C
authors.lastname: Rogers
authors.forename: M
authors.initials: M
authors.lastname: Okada
authors.forename: J
authors.initials: J
authors.lastname: Manfreda
mesh_terms: D000293:Adolescent; D000328:Adult; D000393:Air Pollutants / Q000009:adverse effects*; D000485:Allergens / Q000276:immunology; D001249:Asthma / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology*; D002648:Child; D003139:Common Cold / Q000150:complications*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000009:adverse effects; D006255:Rhinitis, Allergic, Seasonal / Q000175:diagnosis; D013458:Sulfur Dioxide / Q000009:adverse effects
chemical_list: D000393:Air Pollutants; D000485:Allergens; D013458:Sulfur Dioxide; D009569:Nitric Oxide