Separate and combined effects of the outdoor and indoor air quality on chronic respiratory symptoms adjusted for allergy among preadolescent children.

The purpose of the study was (a) to assess whether the respiratory effects of outdoor air pollutants may be replicated after correcting for indoor air quality (environmental tobacco smoke, home heating and damp or mold houses), (b) to evaluate whether the extent of the allergic status of children modifies the respiratory health due to air pollution, and (c) to determine whether the higher prevalence of respiratory symptoms in more polluted areas of the city may be explained by excess in allergy. The survey targeted 1,129 school children, nine years of age, attending schools in Cracow, located in the areas with different levels of the outdoor air pollution. Based on the measurements obtained from the air pollution monitoring stations and the information provided by parents on the sources of local emission of air pollutants, four categories of air pollution areas have been defined. Chronic phlegm as a single symptom was unrelated to allergy but associated with the outdoor air pollution score. The prevalence odds ratio (OR) for this symptom between the contrasting areas of outdoor air pollution, i.e. very high pollution versus very low, was 5.85 (95% CI: 1.05-32.6). Except for chronic phlegm, the outdoor air pollution score was associated only with hay fever when adjusted for indoor characteristics and allergy. After adjustment for air pollution and allergy, the presence of molds or dampness in the house was significantly related to hay fever (OR = 2.1, 95% CI: 1.5-3.0), wheezing (OR = 1.6, 95% CI: 1.1-2.5), and difficulty in breathing (OR = 2.0, 95% CI: 1.2-3.3). In terms of attributable fraction (AF(pop)), the effect of outdoor air pollution on the occurrence of allergy in children was significant (AF(pop) = 22.3%). The impact of allergy on the occurrence of respiratory symptoms (two or more respiratory symptoms) was stronger (AF(pop) = 52.1%) than that of the outdoor air pollution level (AF(pop) = 21.6%) or that of molds/dampness at home (AF(pop) = 14.1%).