Air pollution and respiratory disease in children: what is the clinically relevant impact?

Acute exposure to air pollution is associated with increased respiratory symptoms and decreases in lung function in children. Most of the respiratory symptoms are nonspecific and not severe. However, lower respiratory symptoms and extra use of bronchodilators may be increased by about one third with exposure to peak levels of ozone in children with asthma. Sensitivity to air pollution does not seem to be determined by the severity of preexisting asthma and there is no indication that new cases of asthma are induced by ozone exposure. However, hospital and outpatient admissions for children with preexisting asthma may be increased in the range of 20% with acute exposure to ambient ozone peaks and possibly with increased sulfur dioxide. This indicates a significant impact of acute effects of air pollution on respiratory health in children, and an increase in the use of medical resources which will vary with the local exposure level and duration. Chronic exposure to increased levels of respirable particles, SO2 and NO2 are associated with up to threefold increases in nonspecific respiratory symptoms such as chronic cough, but not with asthma. Exposure to high traffic flow has been found to lead to significant increases in respiratory symptoms, while no clear effect on the inception of asthma has been documented. Although these symptoms are usually not severe, they will contribute to an increased use of pediatric health care facilities. It appears unlikely that long-term exposure to pollutants or irritants is responsible for the secular increase in asthma and allergy observed in Western countries. Whether exposure to car traffic is a significant risk factor for acute asthma or its inception remains to be clarified.