Defining childhood atopic phenotypes to investigate the association of atopic sensitization with allergic disease

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Abstract
Aims: Although atopic sensitization is common in childhood, its relationship to clinical allergic disease remains incompletely understood. We therefore sought to explore this relationship by defining sensitization based atopic phenotypes. Methods: Children were recruited at birth (n = 1456) and reviewed at 1, 2, 4 and 10 years. Skin prick testing (SPT) to common allergens was done at 4 (n = 980) and 10 years (n = 1036) with lung function (n = 981), bronchial challenge (n = 784) and serum IgE (n = 953) testing at 10. Atopic phenotypes were defined, by sensitization pattern, for children with SPT at both 4 and 10 years (n = 823). Results: Of phenotyped children, 68.0% were never atopic, 4.3% early childhood atopic (only atopic at age 4), 16.5% chronic childhood atopics (at 4 and 10 years) and 11.2% delayed childhood atopics (only at 10). Never atopics showed small but identifiable prevalence of allergic diseases such as asthma, eczema and rhinitis. Amongst allergen-sensitized subjects, aeroallergen predominated over food sensitization throughout childhood. Chronic childhood atopics showed highest prevalence of lifetime plus persistent wheeze, eczema and rhinitis, increased prevalence of aeroallergen sensitization, some evidence of persistent food sensitization, significantly greater cord IgE than never atopics (P = 0.006), plus higher total IgE (P < 0.001) and bronchial hyper-responsiveness (P < 0.001) at 10 years than other phenotypes. Conclusion: A proportion of childhood eczema, rhinitis and asthma is nonatopic. The commonest childhood pattern of atopy is chronic sensitization, associated with early, persisting and clinically significant allergic disease. The currently accepted childhood ‘Allergic March’ may oversimplify the natural history of childhood atopy and allergic disease.