Public Release: 

Exposure to traffic pollution increases asthma severity in pregnant women

American Thoracic Society

ATS 2013, PHILADELPHIA ─ Air pollutants from traffic are associated with increased asthma severity levels in pregnant asthmatic women, according to a new study.

"Air pollution is a known trigger for asthma symptoms," said lead author Janneane Gent, PhD, Research Scientist in Epidemiology (Environmental Health) at the Yale School of Public Health. "In our study, exposures were assessed using a sophisticated air pollution modeling system (Community Multiscale Air Quality, CMAQ) that permits community-level estimates (i.e., close to where the subject resides) instead of assigning regional measurements made at Environmental Protection Agency (EPA) central site monitors to all subjects. Using community-level estimates, we found that exposure to nitrogen dioxide at levels much lower than the current EPA standard was associated with increased risk of asthma morbidity."

The results of the study will be presented at the ATS 2013 International Conference.

The study enrolled 637 pregnant women (<24 weeks gestation) with active asthma (physician-diagnosed asthma plus symptoms and/or asthma medication use in the previous 12 months) from Connecticut and Western Massachusetts. Asthma severity levels, measured by days of wheeze, medication use, and a 5-level asthma severity score were assessed through phone interviews for each 28-day gestational month.

Exposure to nitrogen dioxide, fine particulate matter, and the elemental carbon content of fine particulate matter were estimated using the CMAQ modeling system. Analyses of the relationship between exposure to traffic-related pollutants and asthma severity were adjusted for a number of possible confounding factors, including month of pregnancy, pre-pregnancy body mass index, demographics, health, household exposures and season.

Mean community-level predicted concentrations for nitrogen dioxide, elemental carbon and fine particulate matter were 23.7 parts per billion (ppb), 0.67 micrograms (one-millionth of a gram) per cubic meter of air (g/m3) and 11.1 g/m3, respectively.

Each 10 ppb increase in community-level nitrogen dioxide was associated with an increased risk of wheeze, with an odds ratio (the odds that an outcome will occur after a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure) of 1.27. Each 10 ppb increase in nitrogen dioxide was also associated with a higher asthma severity score (odds ratio 1.31). Similarly, each 0.5 g/m3 increase in elemental carbon was associated with an increased risk of wheeze (odds ratio 1.30) and higher asthma severity score (odds ratio 1.32).

Exposure to fine particulate matter did not significantly increase asthma morbidity or asthma severity score.

"Exposure to air pollution from traffic is known to have a number of deleterious effects on human health," said Dr. Gent. "Our study suggests that exposures to community-level concentrations of traffic-related pollutants are associated with increased asthma morbidity, and that these pollutant concentrations are likely to be lower than those measured at EPA central monitoring sites."


* Please note that numbers in this release may differ slightly from those in the abstract. Many of these investigations are ongoing; the release represents the most up-to-date data available at press time.

Abstract 38621

Asthma Severity During Pregnancy: Effect Of Community-Level Exposure To Traffic-Related Pollutants
Type: Scientific Abstract
Category: 01.08 - Asthma: Epidemiology (EOH)
Authors: J.F. Gent1, J.M. Kezik1, T.R. Holford1, M.E. Hill1, L. McKay1, K. Belanger1, M.B. Bracken1, K. Demerjian2, B.P. Leaderer1; 1Yale University School of Public Health - New Haven, CT/US, 2State University of New York - Albany, NY/US

Abstract Body

Rationale: In a study of pregnant, asthmatic women (n=637) living in Connecticut and Western Massachusetts, we assessed the association between symptoms and medication use and community-level exposures to nitrogen dioxide (1-hr maximum NO2), fine particles (24-hr mean PM2.5), and elemental carbon content of PM2.5 (24-hr mean). Exposures were estimated using the high-resolution Community Multiscale Air Quality (CMAQ) model which predicts community-level values in 12x12 km grids. Methods: Women with active asthma (physician-diagnosed asthma plus symptoms and/or asthma medication use in the previous 12 months) were recruited before 24 weeks gestation. Subjects' home addresses were geocoded for assignment to pollution exposure grids. Symptoms and medication use for each 28-day gestational month were collected through phone interviews. Outcome measures included days of wheeze (categorized as 0, 1-7, > 7 but not daily, daily) and monthly 5-level asthma severity score (adapted from Global Initiative for Asthma guidelines). Effects of exposures (daily estimates averaged over gestational month) to NO2, elemental carbon and PM2.5 on asthma morbidity were examined with hierarchical, ordered logistic regression analyses using generalized linear mixed models adjusted for covariates related to pregnancy (month of pregnancy, pre-pregnancy body mass index); demographics and health (age, ethnicity, education level, allergies, [asthma medication use for models with wheeze]); household exposures (gas stove, reported mold or mildew, use of tobacco);and season. Results: Mean (standard deviation) community-level concentrations for NO2, elemental carbon and PM2.5, respectively were: 23.7 (8.6) ppb, 0.67 (0.25) g/m3 and 11.1(2.7) g/m3. In single pollutant models adjusted for covariates, each 10 ppb increase in community-level NO2 was associated with an increased risk of wheeze (odds ratio [OR] 1.27, 95% confidence interval [CI] 1.10, 1.46) and higher asthma severity score (OR 1.31, 95% CI 1.16, 1.49). Each 0.5 g/m3 increase in elemental carbon was associated with an increased risk of wheeze (OR 1.30, 95% CI 1.06, 1.58) and higher asthma severity score (OR 1.32, 95% CI 1.10, 1.58). No significant effects on asthma morbidity were observed for exposure to PM2.5 (wheeze OR 1.09, 95% CI 0.95, 1.25; severity score OR 1.08, 95% CI 0.96, 1.21). Conclusion: Risk of increased asthma morbidity during pregnancy is significantly associated with exposure to ambient levels of traffic-related pollutants NO2 and the elemental carbon content of PM2.5. Health effects were associated with community-level estimates of NO2 at concentrations much lower than the EPA 1-hr maximum standard of 100 ppb. There currently is no EPA standard for elemental carbon.

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