Increased Asthma Severity among Children Exposed to Outdoor NO2

Abstract

ISEE-0361 Background and Objectives: Recent literature suggests that outdoor concentrations of NO2 (primarily associated with motor vehicles) or living close to highways may be associated with asthma exacerbation (increase in symptoms, medication use and health care utilization) in asthmatic children. Methods: In CT and MA, 1400 children with active asthma (age 5-10) were enrolled in a prospective study. Palmes tubes measured NO2 outside their homes for 4 weeks. Parents used daily calendars to record symptom and medication use, to report to a research assistant at the end of the monitoring period. These data were used to classify asthma severity using the Global Initiative for Asthma (GINA, 2002) criteria, as mild intermittent, mild persistent, moderate, or severe. The analysis was stratified by season to control for the differing time spent outdoors and ordered logistic regression models controlled for ethnicity, mother's age and education, and housing type (single vs. multi-family). Results: Mean (SD) NO2 concentrations were 10.7 ppb (3.8) in the winter months, 8.7 ppb (3.4) in the spring, 9.8 ppb (3.1) in the summer and 12.6 ppb (3.7) in the fall. No increased asthma severity was associated with NO2 exposure during the cooler months. Among 227 children measured during the summer, 145 played outdoors at least half of the days during the monitoring period. Among these children, an increase of 5 ppb in NO2 was associated with an increased risk (odds ratio = 2.0, 95% CI 1.2-3.5) for a one category increase in GINA asthma severity (e.g. moderate to severe). No increased risk was associated with NO2 exposure for children who did not play outdoors half of the days (odds ratio = 1.2, 95% CI 0.6-2.4). Conclusion: Exposure to outdoor NO2, at levels well below the US Environmental Protection Agency standard (53 ppb), is associated with significant risk for increased asthma severity in children who spend time outdoors.