Original article
The International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three: A global synthesis

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Abstract

This ISAAC Phase Three synthesis provides summarised information on the main findings of the study, regional tables and figures related to the prevalence and severity of current symptoms of asthma, rhinoconjunctivitis and eczema in the main regions of the world. The large number of surveyed children (≈1,200,000), the large number of centres (233) and countries (98) that participated in ISAAC Phase Three makes this study the most comprehensive survey of these diseases ever undertaken. Globally, the prevalence for current asthma, rhinoconjunctivitis and eczema in the 13–14-year age group was 14.1%, 14.6% and 7.3%, respectively. In the 6–7-year age group the prevalence for current asthma, rhinoconjunctivitis and eczema was 11.7%, 8.5% and 7.9%, respectively. The study shows a wide variability in the prevalence and severity of asthma, rhinoconjunctivitis and eczema which occurs not just between regions and countries but between centres in the same country and centres in the same city. This study definitively establishes that the prevalence of those diseases can be very high in non-affluent centres with low socioeconomic conditions. The large variability also suggests a crucial role of local environment characteristics to determine the differences in prevalence between one place and another. Thus, ISAAC Phase Three has provided a large body of epidemiological information on asthma, rhinoconjunctivitis and eczema in childhood from contrasting environments which is expected to yield new clues about the aetiology of those conditions and reasons for their marked global variability.

Introduction

Asthma, rhinoconjunctivitis and eczema in childhood have become three of the more important public health problems worldwide. Although in the past it was thought that these diseases occurred more frequently in populations from developed countries, it has been evident since the first global report from the International Study of Asthma and Allergies in Childhood (ISAAC) that prevalence of those conditions in some low-resourced countries was similar or even higher than in developed ones and that a wide variability in their prevalence occurred at regional and even at country level.1, 2, 3, 4

Since then, a large body of new national, regional and global information on the prevalence, severity, risk factors, trends and several other aspects related to asthma, rhinoconjunctivitis and eczema in childhood, has been reported by ISAAC.5 The recently completed third ISAAC Phase included the largest number of centres from the main world regions ever studied in regard to these conditions, with about 1,200,000 schoolchildren surveyed; detailed information on the global prevalence and severity of asthma, rhinitis and eczema has been reported in the ISAAC world map journal articles.6, 7, 8

The well-known methodological consistency of the ISAAC programme, its originality and especially the inclusion of countries with different cultures, socioeconomic development and lifestyles, has led to its results being employed by several governmental and academic institutions at country and regional level. It has constituted the epidemiological basis for many of the well-known global initiatives on asthma, rhinitis and eczema management in childhood, and for guidelines and recommendations from international health organisations.

This article presents new information on disease overlap (asthma, rhinoconjunctivitis, eczema), socioeconomic and geospatial considerations from ISAAC Phase Three (written questionnaires) concerning the prevalence of asthma, rhinoconjunctivitis and eczema in children aged 6–7 and 13–14 years.

Section snippets

Methods

The detailed methodology employed by ISAAC to obtain and analyse data for Phase Three, has already been published in detail elsewhere.5, 9 Briefly, written questionnaires were self-completed at school by 13–14-year olds and completed at home by parents of 6–7-year olds. Samples of 3000 children for each age group (with a minimum of 1000) within each centre were selected by randomly sampling schools within the study area. Almost all centres studied the 13–14-year age group, but only some centres

Participants

ISAAC Phase Three surveyed about 1,200,000 children from 233 centres in 98 countries, involving almost 800,000 children aged 13–14 years and almost 400,000 aged 6–7 years. For asthma the data sets comprised 1,187,496 schoolchildren from 233 centres in 98 countries, of whom 128 centres (689,413 participants) in 64 countries (34 countries new to ISAAC) had not undertaken ISAAC Phase One; 798,685 were aged 13–14 years and 388,811 were aged 6–7 years. The majority of the new ISAAC centres were from

Discussion

This is the largest study of asthma, rhinoconjunctivitis and eczema ever conducted, and the first time that the relationship between the three diseases, and various geospatial and geo-climatic phenomena has been examined. ISAAC Phase Three was performed in all WHO regions thus the main continents and ethnic areas of the world were represented in the study.

The large variability of prevalence between regions, continents, countries, centres in the same country, and even between centres in the same

Ethical disclosure

Protection of human and animal subjects. The authors declare that no experiments were performed on humans or animals for this investigation.

Right to privacy and informed consent. The authors declare that no patient data appears in this article.

Confidentiality of data. The authors declare that no patient data appears in this article.

Conflict of interest

The named authors declare that they have no conflict of interest.

Funding

Currently the main source of funding for the ISAAC International Data Centre (IIDC) is the New Zealand Lottery Board. Many New Zealand funding bodies have contributed support for the IIDC during the periods of fieldwork and data compilation (the Health Research Council of New Zealand, the Asthma and Respiratory Foundation of New Zealand, the Child Health Research Foundation, the Hawke's Bay Medical Research Foundation, the Waikato Medical Research Foundation, Glaxo Wellcome New Zealand, the

Acknowledgements

All authors participated in the development, design, analysis, and interpretation of this work and in the writing of this paper. We are grateful to the children and parents who participated in ISAAC Phase Three and the coordination and assistance by the school staff is sincerely appreciated. The authors also acknowledge and thank the many funding bodies throughout the world that supported the individual ISAAC centres and collaborators and their meetings.

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