title: Severe and Moderate Asthma Exacerbations in Asthmatic Children and Exposure to Ambient Air Pollutants.
abstract: It is well established that short-term exposure to ambient air pollutants can exacerbate asthma, the role of early life or long-term exposure is less clear. We assessed the association between severe asthma exacerbations with both birth and annual exposure to outdoor air pollutants with a population-based cohort of asthmatic children in the province of Quebec (Canada).
  
  
  
  Exacerbations of asthma occurring between 1 April 1996 and 31 March 2011 were defined as one hospitalization or emergency room visit with a diagnosis of asthma for children (<13 years old) already diagnosed with asthma. Annual daily average concentrations of ozone (O₃) and nitrogen dioxide (NO₂) were estimated at the child's residential postal code. Satellite based levels of fine particulate (PM2.5) estimated for a grid of 10 km by 10 km were also assigned to postal codes of residence for the whole province. Hazard ratios (HRs) were estimated from Cox models with a gap time approach for both birth and time-dependant exposure.
  
  
  
  Of the 162,752 asthmatic children followed (1,020,280 person-years), 35,229 had at least one asthma exacerbation. The HRs stratified by age groups and adjusted for the year of birth, the ordinal number of exacerbations, sex, as well as material and social deprivation, showed an interquartile range increase in the time-dependant exposure to NO₂ (4.95 ppb), O₃ (3.85 ppb), and PM2.5 (1.82 μg/m³) of 1.095 (95% CI 1.058-1.131), 1.052 (95% CI 1.037-1.066) and 1.025 (95% CI 1.017-1.031), respectively. While a positive association was found to PM2.5, no associations were found between exposure at birth to NO₂ or O₃.
  
  
  
  Our results support the conclusion, within the limitation of this study, that asthma exacerbations in asthmatic children are mainly associated with time dependent residential exposures less with exposure at birth.
authors.affiliation: Department of Environmental and Occupational Health, School of Public Health, University of Montreal, Montréal, QC H2L 1M3, Canada. louis-francois.tetreault@umontreal.ca.|Direction Régionale de Santé Publique du CIUSSS Centre-Sud-de-l'Île-de-Montréalde Montréal, Montréal, QC H2L 1M3, Canada. louis-francois.tetreault@umontreal.ca.
authors.forename: Louis-Francois
authors.initials: LF
authors.lastname: Tétreault
authors.affiliation: Institut Natonal de la Santé Publique du Québec, Québec, QC H2L 1M3, Canada. marieve.doucet.1@ulaval.ca.|Department of Medicine, Laval University, Québec, QC H2L 1M3, Canada. marieve.doucet.1@ulaval.ca.
authors.forename: Marieve
authors.initials: M
authors.lastname: Doucet
authors.affiliation: Institut Natonal de la Santé Publique du Québec, Québec, QC H2L 1M3, Canada. philippe.gamache@inspq.qc.ca.
authors.forename: Philippe
authors.initials: P
authors.lastname: Gamache
authors.affiliation: Direction Régionale de Santé Publique du CIUSSS Centre-Sud-de-l'Île-de-Montréalde Montréal, Montréal, QC H2L 1M3, Canada. mfournie@santepub-mtl.qc.ca.
authors.forename: Michel
authors.initials: M
authors.lastname: Fournier
authors.affiliation: Institut Natonal de la Santé Publique du Québec, Québec, QC H2L 1M3, Canada. allan.brand83@gmail.com.
authors.forename: Allan
authors.initials: A
authors.lastname: Brand
authors.affiliation: British Columbia Centre for Disease Control, Vancouver, BC V5Z 4R4, Canada. tom.kosatsky@bccdc.ca.
authors.forename: Tom
authors.initials: T
authors.lastname: Kosatsky
authors.affiliation: Department of Environmental and Occupational Health, School of Public Health, University of Montreal, Montréal, QC H2L 1M3, Canada. audrey.smargiassi@umontreal.ca.|Institut Natonal de la Santé Publique du Québec, Québec, QC H2L 1M3, Canada. audrey.smargiassi@umontreal.ca.|Université de Montréal Public Health Research Institute, Montreal, QC H2L 1M3, Canada. audrey.smargiassi@umontreal.ca.
authors.forename: Audrey
authors.initials: A
authors.lastname: Smargiassi
mesh_terms: D000293:Adolescent; D000393:Air Pollutants / Q000009:adverse effects* / Q000032:analysis; D000397:Air Pollution / Q000009:adverse effects* / Q000032:analysis; D001249:Asthma / Q000453:epidemiology / Q000209:etiology*; D002170:Canada; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009585:Nitrogen Dioxide / Q000032:analysis; D010126:Ozone / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis; D011792:Quebec / Q000453:epidemiology
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D010126:Ozone; D009585:Nitrogen Dioxide
keywords: air pollution; asthma; childhood; exacerbation