ISAAC Phase Three


Initially, ISAAC Phase Three wished to investigate divergent time trends which were of particular interest in exploring the role of environmental factors. However, there was enormous interest from centres that had not previously undertaken ISAAC as these centres were anecdotally experiencing increasing prevalences of these conditions and wished to document this by participating in ISAAC Phase Three.


The specific aims of ISAAC Phase Three were:

  1. To examine time trends in the prevalence of asthma, allergic rhinoconjunctivitis and atopic eczema in centres and countries which participated in ISAAC Phase One (Phase 3A centres).
  2. To describe the prevalence and severity of asthma, allergic rhinoconjunctivitis and atopic eczema in centres and countries which did not participate in Phase One (Phase 3B centres).
  3. 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.

The details of Phase Three are published in the Phase Three Manual.


ISAAC Phase Three repeated Phase One after at least five years for centres that undertook Phase One (time trends analyses). New centres which did not do Phase One (enlarged worldwide prevalence maps) were included, and an environmental questionnaire (EQ) was added. The EQ asked questions about diet, height, weight, heating and cooking fuels, exercise, pets, family size and birth order, socioeconomic status, immigration and tobacco smoke exposure. The Phase Three field work was conducted during 2001-3. The design of Phase Three corresponded to the Phase One study design. The same sampling frame, method of selecting schools and method of selecting children within schools was used. Where necessary, questionnaires were translated into local languages using the translation guidelines set out in Phase One. A list of languages questionnaires have been translated into can be found in the resources section under 'Tools'.

Time period

The time period between Phase One and Phase Three data collection was at least 5 years. This was chosen to be short enough to detect changes in centres where environmental changes may occur rapidly, as in low prevalence countries such as Greece and China, but not too short for centres where environmental changes may occur more slowly, as in high prevalence countries such as New Zealand and USA. 85% of centres conducted Phase Three 6-8 years after Phase One, on average 7 years later.


ISAAC Phase Three has obtained the first internationally comparable estimates of direction and magnitude of change in symptoms of asthma, rhinoconjunctivitis and atopic eczema. ISAAC Phase Three showed that in developing countries asthma and allergic disease were increasing1,2,3,4, and analyses of potential risk and protective factors that may have contributed to these increases have been published5,6,7,8,9,10,11,12,13,14.

Until ISAAC Phase Three, only 5 centres in the world had previously studied time trends in all 3 conditions, so the time trends results in 2 age groups from 104 centres in 55 countries has provided very helpful new information. In many regions with developing countries, an increase in the prevalence of symptoms was found more commonly than a decrease in the prevalence of symptoms for all 3 conditions. In centres where asthma symptom prevalence had previously been low, it mostly increased, and where it had been high it mostly decreased or did not change. The rise in prevalence of symptoms in many centres is of major concern, but the absence of rises of prevalence for previously high prevalence centres such as New Zealand is reassuring. The divergent time trends in prevalence of symptoms of allergic diseases form the basis for further aetiological research, which may include examination of lifestyle, dietary habits, microbial exposure, economic factors, indoor environment, outdoor environment, climatic variation, awareness of disease and management of symptoms.

The inclusion of new centres in predominantly developing countries in Phase Three showed us that in children and adolescents, asthma, rhinoconjuncitivitis and eczema was a growing problem and that further research is necessary to investigate trends in these developing countries and to identify and investigate environmental risk factors that contribute to these increases.

Now that ISAAC has "mapped" the prevalence of asthma, rhinoconjunctivitis and eczema in 237 centers in 98 countries involving 1,187,496 children and adolescents, more research is urgently required to further develop interventions to prevent these increases.

Funding of ISAAC Phase Three

As with ISAAC Phase One, ISAAC Phase Three was open to any collaborator who agreed to adhere to the protocol and each centre was requested to provide it's own funding. The programme was funded by the many funding bodies throughout the world that supported the individual ISAAC centres and collaborators and their meetings. In New Zealand ISAAC was funded by 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 NZ Lottery Board and Astra Zeneca New Zealand. Travel grants were awarded by the Auckland Medical Research Foundation and the Maurice & Phyllis Paykel Trust. Glaxo Wellcome International Medical Affairs supported the regional coordination and the ISAAC International Data Centre. The ISAAC International Data Centre is currently funded by grants from the BUPA Foundation, the Auckland Medical Research Foundation and the NZ Lottery Board.