Geographic variations in the effect of atopy on asthma in the European Community Respiratory Health Study

Background: Atopy has long been related to asthma. The prevalences of both atopy and asthma have shown substantial variation. Objective: We sought to assess geographic variations in the fraction of asthma attributable to IgE sensitization to specific allergens in the European Community Respiratory Health Survey. Methods: A cross-sectional study was undertaken during the years 1991 and 1992 on 13,558 individuals in 36 centers in 16 countries. Asthma was defined in several ways, variously incorporating reported symptoms, bronchial responsiveness to methacholine, and physician diagnosis. Specific IgE against house dust mite (Dermatophagoides pteronyssinus), cat, timothy grass, Cladosporium herbarum, and a local allergen (birch, Parietaria judaica, or ragweed) were measured. Results: The overall attributable fraction (AF) of asthma symptoms caused by atopy was 30% but varied widely between centers, ranging from 4% to 61%. The overall AF increased to 43% when asthma was based on wheezing and bronchial responsiveness, to 45% with a physician diagnosis of asthma, and to 48% when the patient reported more than 12 attacks in the last year. Between centers, the AF for atopy was significantly correlated with the prevalence of atopy among the asthmatic patients (r = 0.91) and with the sensitization to house dust mite (r = 0.64), as well as with the prevalence of asthma among atopic individuals (r = 0.43) and the prevalence of asthma among nonatopic individuals (r = -0.51). Conclusion: The effect of atopy on the prevalence of asthma varies widely between centers, probably because of variations in factors related to the expression of asthma and to the prevalence of sensitization, particularly to house dust mite.