W. James Gauderman, Edward Avol, Fred Lurmann, Nino Kuenzli ...
Childhood Asthma and Exposure to Traffic and NO2 W. James Gauderman, Edward Avol, Fred Lurmann, Nino Kuenzli, Frank Gilliland, John Peters, and Rob McConnell Epidemiology, Volume 16, Number 6, 2005 Presented by Nina Ewall 1 Paper - Background Irregular 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 2 European studies have been conducted but variables such as home and street design and relative amounts of diesel to gasoline vehicles may vary 3 Purpose To determine whether changes in NO 2 concentrations and indicators of exposure to traffic related pollution are associated with the prevalence of asthma (or indicators of asthma)
4 Participants University of Southern California Childrens 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 monitoring 5 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, Number10 Map of Communities 6 10 Communities Alpine, Atascadero, Lake Elsinore, Lancaster, Long Beach ,Mira Loma, Riverside, San Dimas Santa
Maria and Upland 7 Nitrogen Dioxide Sampling Palmes tube diffusion samplers placed outside each home for 2 week periods in summer (mid Aug.) and fall (mid Nov.) 2000 208 valid measurements (91%) for both seasons 10% subjects homes received duplicate samplers and travel field blanks 2 meters above ground (roofline eaves, signposts, rain gutters) 8
Traffic Pollution Exposure - Measurements Distance 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) 9
Models Source Calculation of vehicle counts near homes (within 150 meters) was derived from daily traffic volumes California Department of Transportation Highway Performance Monitoring System, 2000 or CALTRANS Model 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 rates 10
12 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 Asthma Questionnaire 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 pets Parents were unaware of the focus of the study at the time of completing the survey (self report bias) 12 Statistical Analysis A regression models were developed to obtain relationships for each traffic indicator and asthma prevalence Natural log transformation (positively skewed) Adjustments made for Hispanic ethnicity, cohort (1993
and 1996), race, sex, and indicator variables for study community Separated models for 2 week (each season) and 4 weeks average Odds Ratio (OR) were standardized to average interquartile range (IQR) for asthma and traffic indicators 13 Results 31 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 NO 2 levels occurred from home to home within the communities. Usually variation
increased in higher polluted communities ( exceptions were Mira Loma and Alpine) 14 Results Odds Ratios for 1 IQR (5.7ppb) of exposure (95%CI) Outcome Measured NO2 Distance to
Freeway Doctor diagnosed Asthma 1.83 (1.04-3.22) 1.89 (1.19-3.02) Model based Pollution From Freeways
2.22 (1.36-3.63) 15 Correlations (R) between NO2 concentrations at residences and traffic pollution indicators Freeway distance Model estimates Pollution from freeways Pollution from non freeways Traffic counts within 150 m
-.54 .56 .34 .24 16 Results Why 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 freeways
Some Europe studies found association between asthma and traffic counts near residences Urban geography and homes are closer to heavy traffic 17 TABLE 4. Associations Between Measured NO2 and Asthma-Related Outcomes (n = 208) Distance Measured NO 2 Model based pollution to Freeway
From Freeway Outcome No. OR* (95% CI) OR* (95% CI) OR* (95% CI) Lifetime history of 31 1.83 (1.043.22) 1.89 (1.193.02)
2.56 (1.504.38) Recent wheeze with exercise 2.01 (1.083.72) Current asthma medication use 26 2.19 (1.204.01) 2.04 (1.253.31)
1.92 (1.183.12) *Odds ratio per change of 1 IQR in exposure (see footnotes to Tables 2 and 4). Within the last 12 months. 18 Strengths: Fairly strong associations were found between several indicators of exposure to traffic related air pollution in residences of S. California and asthma history (prevalence) and symptoms (wheezing) Measuring NO2 levels or other relevant agents (PM, CO) is an important way to validate the use of traffic
measurements as indicators of traffic exposure in a study population Failure to validate traffic indicators may explain inconsistent results from other studies. 19 Limitations This is one study in one region and requires validation in other populations and communities. It is unclear whether the prevalence of asthma in the study was related specifically to NO2 concentrations (5.7 ppb low) or a combination of the other various traffic related pollutants associated with NO2 Concentration of fine particulate matter, black smoke (diesel exhaust)
20 Limitations Determination of asthma in questionnaire maybe a reflection of access to healthcare and different diagnostic procedures among doctors . Is there a more precise tool? NO2 and traffic measurements were obtained after the onset of asthma and extrapolated to earlier ages Freeways and major roads have been in the communities for many years 21
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