ISAAC Phase One used simple core written questionnaires for two age groups, and was completed in 156 collaborating centres in 56 countries with a total of 721,601 children participating. In the 13-14 year age group 155 centres from 56 countries participated, of which 99 centres completed a video questionnaire. For the 6-7 year age group there were 91 collaborating centres in 38 countries. ISAAC Phase One Field work commenced in 1993, and was conducted in the majority of centres between 1994 and 1995. ISAAC Phase One demonstrated a large variation in the prevalence of asthma symptoms in children throughout the world including hitherto unstudied populations. It is likely that environmental factors were responsible for the major differences between countries. The results provided a framework for studies between populations in contrasting environments to pursue new clues about the aetiology of asthma. Ecological studies were undertaken using the Phase One data to develop hypotheses about environmental factors.
The aims of ISAAC Phase One were:
- To describe the prevalence and severity of asthma, rhinitis and eczema in children living in different centres and to make comparisons within and between countries;
- To obtain baseline measures for assessment of future trends in the prevalence and severity of these diseases; and
- To provide a framework for further aetiological research into lifestyle, environmental, genetic and medical care factors affecting these diseases.
ISAAC Phase Two involved more intensive studies in a smaller number of selected centres. It began in 1998 and involved 30 centres in 22 countries with 53,383 children participating. Phase Two was designed to investigate the relative importance of hypotheses of interest that arose from the Phase One results. ISAAC Phase Two enabled internationally standardised comparisons of disease and relevant risk factors using the modules developed by ISAAC collaborators (ISAAC Phase Two Modules Manual). These modules include the ISAAC core questionnaires, supplementary questionnaires, including questionnaires on disease management, child contact modules including examination for flexural dermatitis, skin prick tests for atopy, bronchial responsiveness to hypertonic saline, blood sampling and storage for serum IgE and genetic analyses, and a risk factor questionnaire module.
ISAAC Phase Two aims were:
- To describe the prevalence of 'objective' markers of asthma and allergies in children living in different centres, and to make comparisons within and between centres.
- To assess the relation between the prevalence of 'objective' markers of asthma and allergies and the prevalence of symptoms of these conditions in children living in different centres.
- To estimate to what extent the variation in the prevalence and severity of asthma and allergies in children between centres can be explained by differences in known or suspected risk factors or by differences in disease management.
- To explore new aetiologic hypotheses regarding the development of asthma and allergies in children.
ISAAC Phase Three, a repeat of Phase One after at least five years, examined variations in time trends of childhood asthma, rhinoconjunctivitis and eczema around the world, and expanded the world maps of these conditions. It is also assessing the relationship between patterns found and environmental data.
The specific aims of ISAAC Phase Three were:
- To examine time trends in the prevalence of asthma, allergic rhinoconjunctivitis and atopic eczema in centres and countries which participated in ISAAC Phase One.
- To describe the prevalence and severity of asthma, allergic rhinoconjunctivitis and atopic eczema in centres and countries which did not participate in Phase One.
- To examine hypotheses at an individual level which have been suggested by the findings of Phase One, subsequent ecological analyses and recent advances in knowledge.
ISAAC Phase Three was completed in 237 collaborating centres in 98 countries with a total of 1,187,496 children participating. In the 13-14 year age group 233 centres from 97 countries participated. For the 6-7 year age group there were 144 collaborating centres in 61 countries. The majority of the Phase Three field work was conducted during 2001-3.
ISAAC Phase Four is the development and expansion of the scope of the ISAAC website as a resource for ISAAC collaborators especially for those in low and middle income countries. It includes the addition of management plans and other resources that are useful for managing asthma, eczema, and rhinitis.