Global variation in the prevalence and severity of asthma symptoms: Phase Three of the International Study of Asthma and Allergies in Childhood (ISAAC)

Background: Phase Three of the International Study of Asthma and Allergies in Childhood (ISAAC) measured the global prevalence and severity of asthma symptoms in children. Methods: A cross-sectional questionnaire survey of 798 685 children aged 13-14 years from 233 centres in 97 countries, and 388 811 children aged 6-7 years from 144 centres in 61 countries, was conducted between 2000 and 2003 in > 90% of the centres. Results: The prevalence of wheeze in the past 12 months (current wheeze) ranged from 0.8% in Tibet (China) to 32.6% in Wellington (New Zealand) in the 13-14 year olds, and from 2.4% in Jodhpur (India) to 37.6% in Costa Rica in the 6-7 year olds. The prevalence of symptoms of severe asthma, defined as >= 4 attacks of wheeze or >= 1 night per week sleep disturbance from wheeze or wheeze affecting speech in the past 12 months, ranged from 0.1% in Pune (India) to 16% in Costa Rica in the 13-14 year olds and from 0% to 20.3% in the same two centres, respectively, in the 6-7 year olds. Ecological economic analyses revealed a significant trend towards a higher prevalence of current wheeze in centres in higher income countries in both age groups, but this trend was reversed for the prevalence of severe symptoms among current wheezers, especially in the older age group. Conclusion: Wide variations exist in the symptom prevalence of childhood asthma worldwide. Although asthma symptoms tend to be more prevalent in more affluent countries, they appear to be more severe in less affluent countries.