ArticlesWorldwide variation in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISAAC
Introduction
There have been few studies of the population prevalence of allergic rhinitis and atopic eczema, and although hundreds of asthma-prevalence studies have been done in various parts of the world, they have seldom used standard approaches. An exception is the European Community Respiratory Health Survey (ECRHS),1, 2, 3 which involved surveys of asthma and allergic-rhinitis prevalence in adults aged 20–44 years in 48 centres in 22 countries, although only nine centres in six countries were outside of western Europe. The ECRHS suggested that there were regional risk factors for asthma and allergic rhinitis in western Europe, but it did not comprehensively assess the global patterns. For children, the largest standard studies of the prevalences of asthma, allergic rhinitis, or atopic eczema have involved at most four countries.4, 5, 6
Thus, in some respects, the epidemiology of asthma and other allergic disorders is currently similar to that of cancer epidemiology in the 1950s and 1960s, when the international patterns of the incidence of cancer were studied.7 These studies revealed striking international differences that gave rise to many new hypotheses, tested in further epidemiological studies that identified previously unknown risk factors for cancer. These risk factors may not have been in the hypotheses investigated if the initial international comparisons had been confined to few western countries. More specifically, Rose8, 9 has noted that whole populations may be exposed to risk factors for disease (eg, high exposure to housedust-mite allergen) and the patterns may be apparent only when comparisons are made between, rather than within, populations.
Therefore, we carried out systematic, standardised, international comparisons of the prevalence of asthma and allergies to generate new hypotheses and to investigate existing hypotheses in the International Study of Asthma and Allergies in Childhood (ISAAC). The detailed findings for the prevalence and severity of the symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema in children aged 6–7 years and 13–14 years will be reported elsewhere. Here, we give an overview of the findings for children aged 13–14 years (the age-group that was studied by all participating centres), assess the relationship between the findings for the three disorders, and discuss the potential for future ecological and case-control studies.
Section snippets
Methods
Phase one of the ISAAC programme10 used a simple standard approach at minimum cost in as wide a range of centres and countries as possible, based on school populations to ensure high response rates. We decided that phase-one studies would involve no invasive or expensive tests. We recruited collaborating centres through professional networks. Each centre agreed to adhere to the study protocol and to complete a registration document and obtain their own funding. Regional coordinators were
Results
463 801 children aged 13–14 years participated in 155 collaborating centres in 56 countries (table 1). The video questionnaire was used as well as the written questionnaire in 99 (64%) of these centres in 42 countries, for 304 796 children. Response rates were more than 80% in 149 (96%) centres. Written questionnaires were translated into 39 languages, including English (50 centres [32·2%]), Spanish (21 centres [13·5%]), Italian (13 centres [8·4%]), Chinese (nine centres [5·8%]), and Portuguese
Discussion
The ISAAC programme has allowed a worldwide assessment of the prevalence of self-reported symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema in children by standard methods. For many collaborating centres, the measurements were the first in their country of symptoms of these disorders, and for many countries, the participation of more than one centre enabled comparisons within countries. The worldwide variations in rates, and partly the variations seen within some countries,
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