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W. James Gauderman, Edward Avol, Fred Lurmann, Nino Kuenzli, Frank Gilliland, John Peters, and Rob McConnell

Childhood Asthma and Exposure to Traffic and NO2

Epidemiology, Volume 16, Number 6, 2005

Presented by Nina Ewall

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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

Paper - Background

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European studies have been conducted but variables such as home and street design and relative amounts of

diesel to gasoline vehicles may vary

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To 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)

Purpose

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• 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 monitoring

Participants

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Map 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, Number10

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10 CommunitiesAlpine, Atascadero, Lake Elsinore, Lancaster, Long

Beach ,Mira Loma, Riverside, San Dimas Santa Maria and Upland

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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)

Nitrogen Dioxide Sampling

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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)

Traffic Pollution Exposure - Measurements

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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

Models – Source

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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)

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“ 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)

Asthma Questionnaire

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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

Statistical Analysis

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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 NO2 levels occurred from home to home within the communities. Usually variation increased in higher polluted communities ( exceptions were Mira Loma and Alpine)

Results

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ResultsOdds Ratios for 1 IQR (5.7ppb) of exposure

(95%CI)

OutcomeMeasured

NO2

Distance to

Freeway

Model based Pollution From

Freeways

Doctor diagnosed Asthma

1.83(1.04-3.22)

1.89(1.19-3.02)

2.22(1.36-3.63)

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Correlations (R) between NO2 concentrations at residences and traffic pollution indicators

Model estimates Pollution from freeways .56Pollution from non freeways .34Traffic counts within 150 m .24

Freeway distance -.54

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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

Results

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TABLE 4. Associations Between Measured NO2 and Asthma-Related Outcomes (n = 208)

Distance Model based pollution

Measured NO2 to Freeway From Freeway

Outcome 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 use 26 2.19 (1.20–4.01) 2.04 (1.25–3.31) 1.92 (1.18–3.12)

*Odds ratio per change of 1 IQR in exposure (see footnotes to Tables 2 and 4).

†Within the last 12 months.

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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.

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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)

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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

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