SummaryBackground Environmental, cultural and health care differences may account for variation among countries in the prevalence of asthma and respiratory symptoms in teenagers. Objective To examine the prevalence of respiratory symptoms and the level of diagnosis, and to compare determinants of asthma and severe wheeze in two countries. Methods Self-completion questionnaires based on the International Study of Asthma and Allergies in Childhood (ISAAC) protocol were provided to school children in Ireland (Republic and Northern Ireland). In the Republic of Ireland, all children in classes largely aged 13±14 years from 30 postprimary schools were selected by random sampling stratified by school size, composition and Health Board in Spring 1995. In Northern Ireland, all children largely aged 13±14 years of age from 26 postprimary schools were selected by random sampling stratified by school type, composition and Education and Library Board in Spring 1996. Results Questionnaires were completed by 2364 children from Northern Ireland and 2671 from the Republic, about 90% of those eligible to participate. The prevalences of wheeze at various levels of severity, of diagnosed asthma and of treated wheeze were very similar in Northern Ireland and the Republic of Ireland. A significant proportion of those reporting more severe symptomatology (four or more attacks of wheeze in the past 12 months and/or one or more nights disturbed and/or moderate or greater disruption of daily activities and/or speech restriction due to wheeze) had been neither diagnosed nor treated for asthma (20±37%). To investigate the determinants of the more severe symptomatology of asthma or treated wheeze a series of stepwise multiple regression analyses was performed. A history of atopy, cigarette smoking, the possession of a furry pet other than a dog or cat and age were each independently associated with severe wheeze, whilst atopy, a furry pet (as above) and gender were each independently associated with asthma or treated wheeze. Conclusions Cigarette smoking is closely associated with the reporting of significant respiratory symptoms together with atopy and exposure to furry pets. Some 20±37% of severe symptoms were neither diagnosed nor treated as asthma.

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The relationship between a history of respiratory infections (and associated variables) The model selected for FEVo.751 accounted for 800 of the variation in FEVo.75I and no interaction terms were necessary. For FVC I it was necessary to include interactions between sex and "area of residence" and between sex and "history of chronic respiratory disease" and this model accounted for 15 % of the variation. No interaction was needed for FEVo.75/FVC ratio and 10 % of the variation was explained.The number of subjects included in the regression 847