title: Association of short-term increases in ambient air pollution and timing of initial asthma diagnosis among Medicaid-enrolled children in a metropolitan area.
abstract: OBJECTIVE
  We investigated associations of short-term changes in ambient ozone (O3), fine particulate matter (PM2.5) and nitrogen dioxide (NO2) concentrations and the timing of new-onset asthma, using a large, high-risk population in an area with historically high ozone levels.
  
  
  METHODS
  The study population included 18,289 incident asthma cases identified among Medicaid-enrolled children in Harris County Texas between 2005-2007, using Medicaid Analytic Extract enrollment and claims files. We used a time-stratified case-crossover design and conditional logistic regression to assess the effect of increased short-term pollutant concentrations on the timing of asthma onset.
  
  
  RESULTS
  Each 10 ppb increase in ozone was significantly associated with new-onset asthma during the warm season (May-October), with the strongest association seen when a 6-day cumulative average period was used as the exposure metric (odds ratio [OR]=1.05, 95% confidence interval [CI], 1.02-1.08). Similar results were seen for NO2 and PM2.5 (OR=1.07, 95% CI, 1.03-1.11 and OR=1.12, 95% CI, 1.03-1.22, respectively), and PM2.5 also had significant effects in the cold season (November-April), 5-day cumulative lag (OR=1.11. 95% CI, 1.00-1.22). Significantly increased ORs for O3 and NO2 during the warm season persisted in co-pollutant models including PM2.5. Race and age at diagnosis modified associations between ozone and onset of asthma.
  
  
  CONCLUSIONS
  Our results indicate that among children in this low-income urban population who developed asthma, their initial date of diagnosis was more likely to occur following periods of higher short-term ambient pollutant levels.
authors.affiliation: Southwest Center for Occupational and Environmental Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA; Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA.
authors.forename: Judy K
authors.initials: JK
authors.lastname: Wendt
authors.affiliation: Southwest Center for Occupational and Environmental Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA; Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA. Electronic address: Elaine.Symanski@uth.tmc.edu.
authors.forename: Elaine
authors.initials: E
authors.lastname: Symanski
authors.affiliation: Southwest Center for Occupational and Environmental Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA; Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Stock
authors.affiliation: Southwest Center for Occupational and Environmental Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA; Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA.
authors.forename: Wenyaw
authors.initials: W
authors.lastname: Chan
authors.affiliation: Southwest Center for Occupational and Environmental Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA; Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, 1200 Herman Pressler Dr., Houston, TX 77030, USA.
authors.forename: Xianglin L
authors.initials: XL
authors.lastname: Du
mesh_terms: D000293:Adolescent; D000397:Air Pollution / Q000009:adverse effects*; D001249:Asthma / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008484:Medicaid; D009585:Nitrogen Dioxide / Q000009:adverse effects*; D010126:Ozone / Q000009:adverse effects*; D052638:Particulate Matter / Q000009:adverse effects*; D014481:United States; D014505:Urban Population
chemical_list: D052638:Particulate Matter; D010126:Ozone; D009585:Nitrogen Dioxide
keywords: Air pollution; Asthma; Child; Incidence; Medicaid