Vehicle exhaust exposure in an incident case-control study of adult asthma

¹ Dept of Public Health and Clinical Medicine, Umeå University
² Lung and Allergy Research, National Institute of Environmental Medicine, Karolinska Institutet, Stockholm; and OLIN Studies, Dept of Medicine, Sunderby Central Hospital of Norrbotten, Luleå
³ Dept of Ecology and Environmental Science, Umeå University

^* To whom correspondence should be addressed. E-mail: lars.modig{at}envmed.umu.se.

	Abstract

The objective of this case-control study was to evaluate whether traffic-related air pollution exposure at home increases the risk of asthma in adults, and further to compare two commonly used exposure variables and differences between urban and rural living.

Incident cases of asthma and matched controls 20-60 years of age, were recruited in Luleå, Sweden. In total 203 cases and 203 controls were enrolled in the study. Exposure was estimated by traffic flow and measured levels of outdoor NO₂ around each home, respectively. The relation between measured levels of NO₂ and traffic flow was studied with linear regression.

The results indicated a non-significant tendency between living in a home close to a high traffic flow and an increased risk of asthma (OR _all=1.5, 95% CI 0.9-2.5; for long-standing residents OR_>2years=2.4, 95% CI 0.9-6.2). The association between asthma and measured NO₂ was weak and not significant, but skin prick test acted as effect modifier with a significant association among positive. The correlation between traffic flow and outdoor NO₂ was low (r=0.38).

The results suggest that living close to high traffic flows might increase the asthma incidence in adults, while the tendency for NO₂ was almost negligible. Traffic flow and NO₂ had a lower than expected correlation.

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