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Advance Publication

Environ Health Perspect; DOI:10.1289/ehp.1306940

Influence of Urbanicity and County Characteristics on the Association between Ozone and Asthma Emergency Department Visits in North Carolina

Jason D. Sacks,1 Ana G. Rappold,2 J. Allen Davis Jr.,1 David B. Richardson,3 Anna E. Waller,4 and Thomas J. Luben
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1National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; 2National Health and Environmental Effects Research Laboratory, U.S. EPA, Research Triangle Park, North Carolina, USA; 3Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina, USA; 4 Department of Emergency Medicine, University of North Carolina, Chapel Hill, North Carolina, USA
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This EHP Advance Publication article has been peer-reviewed, revised, and accepted for publication. EHP Advance Publication articles are completely citable using the DOI number assigned to the article. This document will be replaced with the copyedited and formatted version as soon as it is available. Through the DOI number used in the citation, you will be able to access this document at each stage of the publication process.

Citation: Sacks JD, Rappold AG, Davis JA Jr., Richardson DB, Waller AE, Luben TJ. Influence of Urbanicity and County Characteristics on the Association between Ozone and Asthma Emergency Department Visits in North Carolina. Environ Health Perspect; http://dx.doi.org/10.1289/ehp.1306940.

Received: 11 April 2013
Accepted: 22 February 2014
Advance Publication: 25 February 2014

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Abstract

Background: Air pollution epidemiology studies, often conducted in large metropolitan areas due to proximity to regulatory monitors, are limited in their ability to examine potential associations between air pollution exposures and health effects in rural locations.

Methods: In a time-stratified case-crossover framework, we examined associations between asthma emergency department (ED) visits in North Carolina (2006-2008) collected by a surveillance system, and short-term ozone exposures using predicted concentrations from the Community Multiscale Air Quality (CMAQ) model. Associations were estimated by county groupings based on four urbanicity classifications (representative of county size and urban proximity) and county health.

Results: Ozone was associated with asthma ED visits in all-year and warm season (April-October) analyses [odds ratio (OR) = 1.019; 95% CI: 0.998, 1.040; OR = 1.020; 95% CI: 0.997, 1.044, respectively, for a 20 ppb increase in lag 0-2 days ozone]. The association was strongest in Less Urbanized counties, with no evidence of a positive association in Rural counties. Associations were similar when adjusted for fine particulate matter in copollutant models. Associations were stronger for children (5-17 years of age) compared with other age groups, and individuals living in counties with poorer health status compared with counties that had the highest health rankings, although estimated associations for these subgroups had larger uncertainty.

Conclusions: Associations between short-term ozone exposures and asthma ED visits differed by overall county health and urbanicity, with stronger associations in Less Urbanized counties, and no positive association in Rural counties. Results also suggest that children are at increased risk of ozone-related respiratory effects.


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