Associations between asthma and bronchial hyper-responsiveness with allergy and atopy phenotypes in urban black South African teenagers.

OBJECTIVES To determine asthma and allergy phenotypes in unselected urban black teenagers and to associate bronchial hyper-responsiveness (BHR) with asthma, other atopic diseases and allergen sensitisation. METHODS This was a cross-sectional study of 211 urban high-school black children of Xhosa ethnicity. Modified ISAAC questionnaires regarding asthma, eczema and rhinitis were administered. BHR was assessed by methacholine challenge using hand-held nebulisers. Skinprick tests (SPTs) were performed for 8 aeroallergens and 4 food allergens. RESULTS Asthma was reported in 9%, and 16 % demonstrated BHR. Rhinitis was reported in 48% and eczema in 19%. Asthma was strongly associated with BHR. Asthma was associated with eczema whereas BHR was associated with rhinitis. SPTs were positive in 34% of subjects, aeroallergens in 32%, and food allergens in 5%. The most common sensitivities were to house dust mites (HDM) and German cockroach. BHR was associated with sensitivity to any aeroallergen, cat, HDM, cockroach and bermuda grass. The number of positive SPTs was associated with asthma and BHR. With each level of SPT positivity, there was 40% increased prevalence of asthma and 70% increased prevalence of BHR. The rate of allergen sensitisation in subjects with BHR (72%) was much higher than those without BHR (28%); house dust mite sensitivity was 69% in subjects with BHR and 18% in those without. CONCLUSIONS These are the highest rates of allergen sensitisation in subjects with BHR documented in an African setting and the widest difference in sensitisation rates between subjects with and without BHR.