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Modification of the Effect of Ambient Air Pollution on Pediatric Asthma Emergency Visits: Susceptible Subpopulations

Strickland, Matthew J.a; Klein, Mitchela; Flanders, W. Danab; Chang, Howard H.c; Mulholland, James A.d; Tolbert, Paige E.a; Darrow, Lyndsey A.b

doi: 10.1097/EDE.0000000000000170
Air Pollution

Background: Children may have differing susceptibility to ambient air pollution concentrations depending on various background characteristics of the children.

Methods: Using emergency department (ED) data linked with birth records from Atlanta, Georgia, we identified ED visits for asthma or wheeze among children 2 to 16 years of age from 1 January 2002 through 30 June 2010 (n = 109,758). We stratified by preterm delivery, term low birth weight, maternal race, Medicaid status, maternal education, maternal smoking, delivery method, and history of a bronchiolitis ED visit. Population-weighted daily average concentrations were calculated for 1-hour maximum carbon monoxide and nitrogen dioxide; 8-hour maximum ozone; and 24-hour average particulate matter less than 10 microns in diameter, particulate matter less than 2.5 microns in diameter (PM2.5), and the PM2.5 components sulfate, nitrate, ammonium, elemental carbon, and organic carbon, using measurements from stationary monitors. Poisson time-series models were used to estimate rate ratios for associations between 3-day moving average pollutant concentrations and daily ED visit counts and to investigate effect-measure modification by the stratification factors.

Results: Associations between pollutant concentrations and asthma exacerbations were larger among children born preterm and among children born to African American mothers. Stratification by race and preterm status together suggested that both factors affected susceptibility. The largest estimated effect size (for an interquartile range increase in pollution) was observed for ozone among preterm births to African American mothers: rate ratio = 1.138 (95% confidence interval = 1.077–1.203). In contrast, the rate ratio for the ozone association among full-term births to mothers of other races was 1.025 (0.970–1.083).

Conclusions: Results support the hypothesis that children vary in their susceptibility to ambient air pollutants.

Supplemental Digital Content is available in the text.

From the aDepartment of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA; bDepartment of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA; cDepartment of Biostatistics, Rollins School of Public Health, Emory University, Atlanta, GA; and dDepartment of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA.

Submitted 26 September 2013; accepted 30 May 2014; posted 4 September 2014.

Funding sources: NIEHS K01ES019877, NIEHS R03ES018963, and EPA STAR grant RD834799. The contents of the publication are solely the responsibility of the grantee and do not necessarily represent the official views of the United States Environmental Protection Agency (U.S. EPA). Further, the U.S. EPA does not endorse the purchase of any commercial products or services mentioned in this publication.

Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article ( This content is not peer-reviewed or copy-edited; it is the sole responsibility of the author.

Correspondence: Matthew J. Strickland, Department of Environmental Health, Rollins School of Public Health, Emory University, 1518 Clifton Rd NE, Atlanta, GA 30322. E-mail:

© 2014 by Lippincott Williams & Wilkins, Inc