Childhood Asthma and Exposure to Traffic and NO2Paper - BackgroundSlide 3PurposeParticipantsSlide 6Slide 7Nitrogen Dioxide SamplingTraffic Pollution Exposure - MeasurementsModels – SourceSlide 11Asthma QuestionnaireStatistical AnalysisResultsSlide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22W. James Gauderman, Edward Avol, Fred Lurmann, Nino Kuenzli, Frank Gilliland, John Peters, and Rob McConnell 1Childhood Asthma and Exposure to Traffic and NO2Epidemiology, Volume 16, Number 6, 2005Presented by Nina EwallIrregular outcomes in studies examining an association between outdoor air pollution and asthma. Why? •Research utilizes different traffic pollution exposure indicators: air monitoring outside home, centralized ambient air monitor, traffic volumes, residential distance to roads, modeling 2Paper - Background3European studies have been conducted but variables such as home and street design and relative amounts of diesel to gasoline vehicles may varyTo determine whether changes in NO2 concentrations and indicators of exposure to traffic related pollution are associated with the prevalence of asthma (or indicators of asthma)4Purpose•University of Southern California Children’s Health Study •1993 / Cohort 1 and 1996 /Cohort 2 • 4th graders (age - 10 years)•10 Southern California Communities (2 of 12 communities were excluded because of minor traffic)•Study requirements – subject stayed in same home since enrolling in the cohort studies•Randomly sampled 229 subjects of 890 children for NO2 monitoring5Participants6Map of Communities Jerrett M, Shankardass K, Berhane K, Gauderman WJ, Kunzlie N, Avol E, Gilliland F, Lurmann F, Molitor J, Molitor J, Thomas DC, Peters J, and McConnell R, Traffic-Related Air Pollution and Asthma Onset in Children: A Prospective Cohort Study with Individual Exposure Measurement, October 2008, Environmental Health Perspectives, Volume116, Number10710 CommunitiesAlpine, Atascadero, Lake Elsinore, Lancaster, Long Beach ,Mira Loma, Riverside, San Dimas Santa Maria and UplandPalmes tube diffusion samplers placed outside each home for 2 week periods in summer (mid Aug.) and fall (mid Nov.) 2000208 valid measurements (91%) for both seasons10% subjects homes received duplicate samplers and travel field blanks2 meters above ground (roofline eaves, signposts, rain gutters)8Nitrogen Dioxide SamplingDistance from home to nearest freeway ( utilized ERSI ArcGIS Version 8.3 / both directions calculated)Average number of travelling vehicles within 150 meters from homes (freeways, arterials, major collector roads and minor roads, if possible)Model estimates of traffic related air pollution at residences, based on dispersion models(Distance to roadways, vehicle counts, vehicle emission rates, and meteorological conditions)9Traffic Pollution Exposure - MeasurementsCalculation of vehicle counts near homes (within 150 meters) was derived from daily traffic volumes•California Department of Transportation Highway Performance Monitoring System, 2000 or CALTRANSModel calculations of traffic related pollution exposure•Based on CALINE4 line source air quality dispersion model•Input variables include roadway geometry, traffic volumes, meteorological conditions (wind speed, wind direction, atmospheric stability, mixing heights) and vehicle emission rates10Models – Source12 – 68% of NO2 levels are from local mobile source emissions.Comparisons •Carbonmonoxide (CO) and fine particulate matter (PM) emissions also assessed to determine pollution exposure•NO2, CO and PM were found to be highly correlated (R>.90)11“ Has a doctor every diagnosed your child as having asthma?” “yes”Asthma related questions•Wheezed in past 12 months•Medication to control Asthma•Wheezed during exercised (12 months)Asthma Risk Factors questions•Parental income, education, tobacco smoking, mildew, water damage, gas stove, pests and petsParents were unaware of the focus of the study at the time of completing the survey (self report bias)12Asthma QuestionnaireA regression models were developed to obtain relationships for each traffic indicator and asthma prevalenceNatural log transformation (positively skewed) Adjustments made for Hispanic ethnicity, cohort (1993 and 1996), race, sex, and indicator variables for study communitySeparated models for 2 week (each season) and 4 weeks averageOdds Ratio (OR) were standardized to average interquartile range (IQR) for asthma and traffic indicators13Statistical Analysis31 of the 208 study participants (15%) had doctor diagnosed asthma NO2 concentration range – 12.9 (Atascadero) to 51.5 ppb (San Dimas) Considerable variation of NO2 levels occurred from home to home within the communities. Usually variation increased in higher polluted communities ( exceptions were Mira Loma and Alpine) 14ResultsResultsOdds Ratios for 1 IQR (5.7ppb) of exposure (95%CI)15OutcomeMeasured NO2Distance toFreewayModel based Pollution From FreewaysDoctor diagnosed Asthma 1.83(1.04-3.22) 1.89(1.19-3.02)2.22(1.36-3.63)16Correlations (R) between NO2 concentrations at residences and traffic pollution indicatorsModel estimates Pollution from freeways .56Pollution from non freeways .34Traffic counts within 150 m .24Freeway distance -.54Why were no associations found between asthma and traffic volumes within 150 meters of homes or model based estimates for non freeway pollution ? Number of vehicles on smaller roads is trivial (10s – 100s) compared to freeways (50,000 – 270,000)Vehicle counts are less accurately estimated on smaller roads in comparison to freewaysSome Europe studies found association between asthma and traffic counts near residencesUrban geography and homes are closer to heavy traffic 17ResultsTABLE 4. Associations Between Measured NO2 and Asthma-Related Outcomes (n = 208) Distance Model based pollution Measured NO2 to Freeway From FreewayOutcome No. OR* (95% CI) OR* (95% CI) OR* (95% CI)Lifetime history of 31 1.83 (1.04–3.22) 1.89 (1.19–3.02) 2.22 (1.36–3.63)Recent wheeze† 43 1.72 (1.07–2.77) 1.59 (1.06–2.36) 1.70 (1.12–2.58)Recent wheeze with exercise† 25 2.01 (1.08–3.72) 2.57 (1.50–4.38) 2.56 (1.50–4.38)Current asthma medication