The prevalence of atopy in asthma in a longitudinal birth cohort

Background: Asthma is often associated with atopy. Cluster analysis shows the prevalence of atopy varies in different phenotypic groups of asthma from 50-90% but no longitudinal studies have assessed how this changes throughout childhood [1]. Our aim was to assess whether atopy precedes an asthma diagnosis, what proportion of asthmatics is atopic at different ages and how these change during childhood, to help decipher the link between the two. Methods: We collected data from a longitudinal birth cohort of 253 subjects, the Perth Infant Asthma Follow up study. A detailed respiratory questionnaire, lung function and skin prick testing were performed at 1, 6 and 12 months, 6, 11, 18 and 24 years. Asthma was physician diagnosed only and atopy was defined by a positive skin prick test. Results: The percentage of asthmatics with atopy rose from 50% at 6 years to 100% at 24 years. Of those with atopic asthma and full sequential data, an atopy diagnosis preceded that of asthma in 45% of cases (n=21) and both were diagnosed in the same time period in 55% (n=26). This was not significantly different. Of those with a history of asthma at 24 years, 90% (n=60) had been diagnosed by 11 years. All subjects with onset of asthma after 11 years of age were atopic. Atopy was less frequent in those with early transient asthma than persistant asthma after 6 years of age (65% vs 80%, p=0.045). Conclusion: The prevalence of atopy is higher in young adult asthmatics than as young children. Both diseases were diagnosed at a similar age in more than 50% of cases, suggesting a common predecessor, rather than a causal relationship. Haldar, P., et al., Cluster analysis and clinical asthma phenotypes. AMJRCCM 2008. 178 (3):218-24.