Effects of air quality on chronic respiratory symptoms adjusted for allergy among preadolescent children

The aim of this study was to assess the respiratory effects of outdoor air pollution after correcting for allergy and indoor air quality. The respiratory health survey targeted 1,129 schoolchildren, 9 yrs of age, attending schools in Krakow located in city areas differing in outdoor air pollution levels. Chronic phlegm as a unique symptom was related neither to allergy nor to indoor variables, but was associated with the outdoor air pollution level (odds ratio (OR): 4.2; 95% confidence interval (CI): 1.1-16.9). The same relationship has been confirmed for the self-reported local sources of industrial air pollution in the area of residence (OR: 4.2; 95% CI: 1.5-11.7). Hay fever appeared to be related to outdoor air pollution level (OR: 1.43; 95% CI: 1.1-2.0) and self-reported heavy traffic (OR: 1.3; 95% CI: 1.0-1.7). In the total sample, wheezing was connected exclusively to allergy and parental atopy, while attacks of dyspnoea with wheezing and asthma diagnosed by physician only were associated with allergy. Since the effect of outdoor pollutants on chronic cough and wheezing (odds ratio: 1.85; 95% confidence interval: 1.03-3.33) was only shown to be significant in the subsample of children without allergy and parental atopy, it may be postulated that either allergy is predisposing to respiratory reactions, or outdoor air pollution is coinvolved in an allergization process of the preadolescent children. Consequently, allergy should be considered as an important confound in epidemiological studies on the respiratory effects of air pollution.