Abstract and Introduction
Abstract
Background: The association between chronic exposure to air pollution and adverse health outcomes has not been well studied.
Objective: This project investigated the impact of chronic exposure to high ozone levels on childhood asthma admissions in New York State.
Methods: We followed a birth cohort born in New York State during 1995-1999 to first asthma admission or until 31 December 2000. We identified births and asthma admissions through the New York State Integrated Child Health Information System and linked these data with ambient ozone data (8-hr maximum) from the New York State Department of Environmental Conservation. We defined chronic ozone exposure using three indicators: mean concentration during the follow-up period, mean concentration during the ozone season, and proportion of follow-up days with ozone levels > 70 ppb. We performed logistic regression analysis to adjust for child's age, sex, birth weight, and gestational age; maternal race/ethnicity, age, education, insurance status, smoking during pregnancy, and poverty level; and geographic region, temperature, and copollutants.
Results: Asthma admissions were significantly associated with increased ozone levels for all chronic exposure indicators (odds ratios, 1.16-1.68), with a positive dose-response relationship. We found stronger associations among younger children, low sociodemographic groups, and New York City residents as effect modifiers.
Conclusion: Chronic exposure to ambient ozone may increase the risk of asthma admissions among children. Younger children and those in low socioeconomic groups have a greater risk of asthma than do other children at the same ozone level.
Introduction
The acute health effects of exposure to ambient ozone have been examined in many geographic regions. Although the findings are inconsistent, potential adverse effects reported include decrements in lung function, airway inflammation, symptoms of asthma, increases in hospitalization for respiratory diseases, and excess mortality (Schwela 2000). On the other hand, the health effects of chronic exposure to ozone have been less studied, and the results are inconclusive. Several studies have reported that long-term exposure to ozone may reduce lung function in school children and adults (Galizia and Kinney 1999; Peters et al. 1999; Qian et al. 2005; Rojas-Martinez et al. 2007) and increase the prevalence of asthma and asthmatic symptoms (Hwang et al. 2005; Ramadour et al. 2000; Wang et al. 1999). In contrast, other studies found an insignificant or negative association between respiratory health effects and chronic ozone exposure (Gauderman et al. 2004; Karr et al. 2007; Zemp et al. 1999). No studies have examined health effects of chronic ozone exposure among a birth cohort. Biologic studies provided plausibility that chronic exposure to ozone is associated with elevated oxidative damage, which might be involved in development of asthma and decrement of lung function (Chen et al. 2007; Mudway and Kelly 2000).
In New York State, asthma hospitalization rates remain considerably higher (20.4 per 10,000) than the U.S. rate of 16.9 per 10,000 population in 2002 (American Lung Association 2004; New York State Department of Health 2005). Young children are a vulnerable population with respect to air pollutants, given their narrow airways, higher breathing rate, developing lungs and immune systems, and more time spent outdoors. Most prior studies have focused on adults and school-age children and analyzed less severe health outcomes than hospitalizations. The effect of chronic exposure to high levels of air pollution in early life and its subsequent impact on childhood asthma admissions is unclear. In addition, the interactive effects between maternal/birth characteristics and air pollution on childhood asthma hospital admissions have rarely been studied. The purpose of this study was to investigate the association between chronic exposure to ozone and childhood asthma admissions. We also examined whether maternal and birth characteristics interacted with the impact of air pollution on asthma hospitalization in early life.