Worldwide trends in the prevalence of asthma symptoms: Phase Three of the International Study of Asthma and Allergies in Childhood (ISAAC)
Abstract
Background: Phase One of the International Study of Asthma and Allergies in Childhood (ISAAC) was designed to allow worldwide asthma symptom prevalence comparisons. In Phase Three we have repeated the Phase One survey in order to assess changes over time.
Methods: The Phase One survey was repeated after an interval of 5-10 years in 106 centres in 56 countries in the 13-14 year age-group (n=304,679), and in 66 centres in 37 countries in the 6-7 year age group (n=193,404).
Results: The average symptom prevalence of current wheeze (in the last 12 months) measured with the written questionnaire changed slightly from 13.2% to 13.7% in the 13-14 year age group (an average increase of 0.06% per year) and from 11.0% to 11.6% in the 6-7 year age group (an average increase of 0.13% per year). There was also little change in the average symptom prevalence of severe asthma, or the symptom prevalence measured with the asthma video questionnaire. However, the time trends in asthma symptom prevalence showed different regional patterns. In Western Europe, current wheeze decreased by -0.07% per year in 13-14 year olds, but increased by 0.20% per year in 6-7 year olds. The corresponding findings for the other regions were: Oceania (-0.39% per year in 13-14 year olds, and -0.21% per year in 6-7 year olds); Latin America (+0.32%, and +0.07% respectively); Northern and Eastern Europe (+0.26%, +0.05%), Africa (+0.16%, +0.10%); North America (+0.12%, +0.32%); Eastern Mediterranean (-0.10%, +0.79%); Asia-Pacific (+0.07%; -0.06%); and the Indian subcontinent (+0.02%, +0.06%). There was a particularly marked reduction in current asthma symptom prevalence in English language countries (-0.51%, -0.09%). Similar patterns were observed for severe asthma (four or more attacks in the previous 12 months). However, the percentage of children reported to have had asthma at some time in their lives increased from 11.2% to 13.8% in the 13-14 year age group (+0.28% per year) and from 9.3% to 10.8% in the 6-7 year age group (+0.18% per year).
Discussion: These findings indicate that international differences in asthma symptom prevalence have reduced, particularly in 13-14 year olds, with decreases in prevalence in English speaking countries and Western Europe and increases in prevalence in regions where prevalence was previously low. Although there was little change in the overall prevalence of current wheeze, the percentage of children reported to have had asthma increased significantly, possibly reflecting greater awareness of this condition and/or changes in diagnostic practice. The asthma symptom prevalence increases in Africa, Latin America and parts of Asia indicate that the global burden of asthma is continuing to rise, but the global prevalence differences are lessening.
