Phase Two Methodology

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. Phase Two enabled internationally standardised comparisons of disease and relevant risk factors using the modules developed by ISAAC collaborators. The sample sizes were smaller than those recommended for Phase One to reflect the more intensive sampling procedures. A sample size of 1000 children per centre was recommended, and the more expensive and invasive tests could optionally be restricted to a stratified sample, comprising a sample of 100 wheezy children and 100 non-wheezy children.

Phase Two measured features of asthma, rhinoconjunctivitis and eczema which were not measured in Phase One. Additional standardised questions about cough, and the medical care of asthma, rhinitis and eczema were also developed. In addition there was a management and a "risk factor" questionnaire. Standardised protocols were also developed for child contact instruments including physical examination of the skin for flexural dermatitis and airway responsiveness testing using hypertonic saline aerosol challenge, skin prick tests for atopy, total and specific serum IgE, and storage of blood samples for genetic analyses and gene-environment interactions and endotoxin and house dust mite antigen measurement in the homes. The bronchial hyperresponsiveness measurement and skin examination were used to see whether these measures showed the same distribution internationally as the questionnaire results for wheeze and atopic eczema. Measures of atopy (using allergen skin tests and IgE measurements) were used to investigate whether variations in symptoms of asthma, rhinoconjunctivitis and eczema are reflected in variations in atopy. Some Phase Two centres also contributed DNA samples which were analysed for both within ISAAC, and as part of a larger asthma genetics consortium, GABRIEL.

ISAAC Phase Two was undertaken in 19 centres from 13 European countries:  Albania, Estonia, France, Germany (2 centres), Greece (2 centres), Iceland, Italy, Latvia, Netherlands, Norway, Spain (4 centres), Sweden (2 centres) and the United Kingdom. The 11 centres outside Europe are in 9 countries: Brazil, China (3 centres), Ecuador, Georgia, Ghana, India, New Zealand, Turkey and Palestine.

Fuller details of Phase Two are published in the Phase Two Manual and in a paper in the European Respiratory Journal.