Background: Individuals with asthma are more atopic than the general population, but few reports have quantified this association, i.e. the proportion of asthma in the community due to specific immunoresponse. We aimed to determine the population attributable risk of asthma in the community due to atopy, and the quantity and quality of specific immunoresponses to common aeroallergens involved.
Methods: We used data from a cross-sectional study in a random sample of the general Spanish population, 20-44 years old, from five areas. In all, 1816 participants were given a symptoms questionnaire, a methacholine challenge and were assessed for atopy. Bronchial responsiveness (BR) was defined as a > or =20% fall in forced expiratory volume in one second (FEV1) after methacholine. Asthma was defined as symptomatic bronchial responsiveness. Atopy was assessed by measuring serum specific IgE or skin tests for sensitivity to Alternaria, birch, cat, Cladosporium, Dermatophagoides pteronyssinus, olive, Parietaria, ragweed or timothy grass.
Results: Sensitivity to any of the individual allergens tested significantly increased the risk of being asthmatic, at least twofold compared to non-atopic individuals. The population attributable risk of atopy in explaining asthma is 41.97% (95% CI: 29.2-60.3) when adjusting for area of residence, age, sex, and smoking. In symptomatic individuals, atopy was an independent factor in producing an early measurable PD20 (methacholine dose producing 20% fall in FEV1), especially in those atopic to two or more aeroallergens, and irrespective of the particular aeroallergen.
Conclusions: Specific immunoresponse is strongly associated with asthma, but positivity to single allergens (quality) and the number of positive immunoresponses (quantity) do not change the per se risk of asthma in atopic individuals.