To access the relationship between atopy and bronchial asthma in adolescents.
A cross-sectional study was conducted. Cluster randomized subgroups of schoolchildren who had participated in ISAAC phase III survey in Guangzhou were enrolled from april to May, 2002. Skin prick test with 5 groups totally for 9 common aeroallergens (dermatophagoides pteronyssinus, Dermatophagoides farinae, cat, Alternaria tenuis, mixed tree pollen, mixed grass pollen, American cockroach, German cockroach and mixed moulds) was performed. Asthma was defined as wheezing or whistling in the chest in the lifetime or in the last 12 months, or diagnosed asthma. Allergy disease was defined as any of asthma, rhinitis and eczema. A wheal size with the diameter of 3 mm or more after subtraction of the negative control was considered as positive and subjects with one or more positive reactions were considered as atopy. The degree of atopy and the sensitivity of the allergen were graded by atopic index (AI) and skin index (SI), respectively.
1543 subjects were selected randomly for the skin prick test, and the response rate was 77.0% (1187/1543). 51.6% (613/1187) were males and 48.4% (574/1187) were females. The median age was 14 years old (range from 12 - 17 years old). The prevalence of asthma was 9.4% (111/1187), among whom 81.1% (90/111) also had rhinitis and 24.3% (27/111) had eczema. Asthma was more prevalent in 686 patients with rhinitis [13.1% (90/686)] or 200 patients with eczema [13.5% (27/200)] than those without rhinitis [4.2% (21/501), OR: 3.444, 95% CI: 2.110 - 5.622, P < 0.01] or eczema [8.5% (84/987), OR: 1.676, 95% CI: 1.055 - 2.663, P < 0.05]. The prevalence of atopy was 46.3% (549/1187) and the positive rates of house dust mite (Der p and Der f) were the highest [41.8% (496/1187) and 42.7% (507/1187), respectively]. Atopy was more common in asthmatic patients [71.2% (79/111)] than in those without any allergic diseases [26.4% (112/425), OR: 6.812, 95% CI: 4.276 - 10.853, P < 0.01]. Asthma was more prevalent in patients with atopy (14.4%) than those without atopy (5.5%, OR: 3.183, 95% CI: 2.075 - 4.883, P < 0.01). The relative risk of having asthma was increased with the higher AI degree. Univariate Logistic regression analysis showed that the risk factors for asthma were Der p (SI >/= 2), Der f (SI = 3 - 4), American cockroach, German cockroach, cat, Alternaria tenuis, mixed grass pollen. Multivariate Logistic regression analysis showed that Der p (SI = 3 - 4), and Alternaria tenuis were independent risk factors for asthma.
Most asthmatic adolescents were allergic to house dust mite in the city of Guangzhou. The risk of asthma was positively correlated with the degree of atopy, as well as the sensitivity to Der p.