ISAAC Phase One


Previous research has looked at the reasons why some individuals rather than others develop asthma and other atopic diseases, such as rhinitis and eczema. A major risk factor was a family history of atopic disease, but various environmental factors have been also considered important in the expression of disease. Such studies within populations have shed little light on the reasons why the occurrence of atopic disease varies from population to population. Factors affecting the prevalence of disease at a population level may be different to those that determine which individuals within a population were at greatest risk. In addition, between populations the relationship between the three atopic conditions may be different. Ecological analyses between populations might reveal further important risk factors. One obstacle to the investigation of population differences (and of trends) had been the lack of a suitable and generally accepted method of measuring the prevalence and severity of asthma and other atopic diseases in children which could be used worldwide. Another obstacle was the absence of a coordinated research programme to obtain and analyse comparative data. The International Study of Asthma and Allergies in Childhood (ISAAC) programme was developed in 1991 to address these issues.


  1. To describe the prevalence and severity of asthma, rhinitis and eczema in adolescents and children living in different centres and to make comparisons within and between countries;
  2. To obtain baseline measures for assessment of future trends in the prevalence and severity of these diseases;
  3. To provide a framework for further aetiological research into lifestyle, environmental, genetic and medical care factors affecting these diseases.


ISAAC Phase One was a multi-centre multi-country cross sectional study involving 2 age groups of school children, 13-14 year old (adolescents) and 6-7 year old(children). Schools were randomly selected from a defined geographical area. Written questionnaires on asthma, rhinitis and eczema symptoms (translated from English) were completed by the adolescents at school, and at home by the parents of the children. An asthma symptoms video questionnaire for the adolescents was optional. A sample size of 3000 per age group was used to give sufficient power (90% at a 1% significance level), and a high participation rate was a requirement. In Phase One over 700,000 children were involved. Field work was conducted in the majority of centres between 1994 and 1995. Data was then sent to the International Data Centre in Auckland, New Zealand, where the methodology was checked and the data analysed.


The new key scientific findings from Phase One were the description of the prevalence and severity of asthma, rhinitis and eczema in these 2 age groups, in 156 centres from 56 countries, most of whom had never undertaken research of this nature before. From the large variations in the prevalence of symptoms of asthma and allergic disease throughout the world (more than 20 fold between centres) and between people of similar genetic origin living in different environments, we concluded that environmental factors were the cause of these large variations1,2,3,4.

Ecological analyses

Ecological analyses using Phase One data were completed between populations.These found possible protection from food of plant origin5, DTP & measles immunization6, TB notifications7, pollen8, outdoor air pollution9 and men smoking10 and a possible risk from higher GNP11, dietary trans fatty acids12, women smoking10 and paracetamol13. There were mixed associations of climate14 and antibiotic sales15 with symptom prevalence. The ecological analyses have played a vital role in suggesting hypotheses that are worthy of further exploration16.

Funding of ISAAC Phase One

ISAAC was open to any collaborator who agreed to adhere to the protocol. Countries in which there was little existing information about asthma, rhinoconjunctivitis and eczema were particularly encouraged to participate. Each centre was responsible for obtaining its own funding. There were many field workers and funding agencies who supported data collection and national, regional and international meetings, including the meetings of the ISAAC Steering Committee. Unfortunately, these are too numerous to mention and are acknowledged elsewhere in local publications. The ISAAC International Data Centre was funded by the Health Research Council of New Zealand, the Asthma and Respiratory Foundation of New Zealand, the National Child Health Research Foundation, the Hawke's Bay Medical Research Foundation, the Waikato Medical Research Foundation, Glaxo Wellcome New Zealand and Astra New Zealand. Glaxo Wellcome International Medical Affairs funded the regional co-ordinating centres.