title: Association of low-level ozone and fine particles with respiratory symptoms in children with asthma.
abstract: BACKGROUND
  Exposure to ozone and particulate matter of 2.5 microm or less (PM2.5) in air at levels above current US Environmental Protection Agency (EPA) standards is a risk factor for respiratory symptoms in children with asthma.
  
  
  OBJECTIVE
  To examine simultaneous effects of ozone and PM2.5 at levels below EPA standards on daily respiratory symptoms and rescue medication use among children with asthma.
  
  
  METHODS
  Daily respiratory symptoms and medication use were examined prospectively for 271 children younger than 12 years with physician-diagnosed, active asthma residing in southern New England. Exposure to ambient concentrations of ozone and PM2.5 from April 1 through September 30, 2001, was assessed using ozone (peak 1-hour and 8-hour) and 24-hour PM2.5. Logistic regression analyses using generalized estimating equations were performed separately for maintenance medication users (n = 130) and nonusers (n = 141). Associations between pollutants (adjusted for temperature, controlling for same- and previous-day levels) and respiratory symptoms and use of rescue medication were evaluated.
  
  
  METHODS
  Respiratory symptoms and rescue medication use recorded on calendars by subjects' mothers.
  
  
  RESULTS
  Mean (SD) levels were 59 (19) ppb (1-hour average) and 51 (16) ppb (8-hour average) for ozone and 13 (8) microg/m3 for PM2.5. In copollutant models, ozone level but not PM2.5 was significantly associated with respiratory symptoms and rescue medication use among children using maintenance medication; a 50-ppb increase in 1-hour ozone was associated with increased likelihood of wheeze (by 35%) and chest tightness (by 47%). The highest levels of ozone (1-hour or 8-hour averages) were associated with increased shortness of breath and rescue medication use. No significant, exposure-dependent associations were observed for any outcome by any pollutant among children who did not use maintenance medication.
  
  
  CONCLUSIONS
  Asthmatic children using maintenance medication are particularly vulnerable to ozone, controlling for exposure to fine particles, at levels below EPA standards.
authors.affiliation: Center for Perinatal, Pediatric, and Environmental Epidemiology, Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, Conn 06510, USA. janneane.gent@yale.edu
authors.forename: Janneane F
authors.initials: JF
authors.lastname: Gent
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Triche
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Holford
authors.forename: Kathleen
authors.initials: K
authors.lastname: Belanger
authors.forename: Michael B
authors.initials: MB
authors.lastname: Bracken
authors.forename: William S
authors.initials: WS
authors.lastname: Beckett
authors.forename: Brian P
authors.initials: BP
authors.lastname: Leaderer
mesh_terms: D000393:Air Pollutants / Q000032:analysis / Q000506:poisoning*; D000397:Air Pollution / Q000009:adverse effects*; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use; D001249:Asthma / Q000139:chemically induced / Q000188:drug therapy / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003237:Connecticut / Q000453:epidemiology; D004417:Dyspnea; D005260:Female; D006801:Humans; D008297:Male; D008404:Massachusetts / Q000453:epidemiology; D010126:Ozone / Q000032:analysis / Q000506:poisoning*; D010316:Particle Size; D012135:Respiratory Sounds; D012720:Severity of Illness Index
chemical_list: D000393:Air Pollutants; D018927:Anti-Asthmatic Agents; D010126:Ozone