Childhood allergies on rise worldwide

The prevalence of childhood allergies such as hay fever has increased in the past decade throughout much of the world, researchers have found.

The International Study of Asthma and Allergies in Childhood first looked at the prevalence of asthma, hay fever and eczema in 1991, and then again in 2002.

Parents of more than 193,400 children aged six or seven from 37 countries were surveyed about symptoms such as wheezing. About 304, 600 children aged 13 to 14 in 56 countries also answered the same questions.

The prevalence —the number of old and new cases during the decade —increased most for the itchy skin condition eczema in the younger age group, and for hay fever for both age groups, findings the study's authors called "concerning."

For the 1,255 children surveyed from Canada:

• Asthma prevalence went up to 18.2 per cent from 14.1 per cent.
• Hay fever increased to 10.8 per cent from 8.2 per cent.
• Eczema symptoms increased to 12.0 per cent from 8.7 per cent.

In the older group, where prevalence of asthma had previously been high, symptoms commonly decreased.

The Asia-Pacific region and India were the only regions where prevalence of all three disorders occurred more often in both age groups.

"Although changes in mean annual prevalence to the order of 0.5 per cent might sound small, such changes could have substantial public-health implications, especially since the increases took place most commonly in heavily populated countries," Prof. Innes Asher of the University of Auckland, New Zealand, and her colleagues wrote in Saturday's issue of the medical journal The Lancet.

The variations in worldwide prevalence of symptoms for the three disorders, even in genetically similar groups, suggest environmental factors such as economic status, dietary habits, climate, infections and pollens might affect the variation, the researchers said.

The findings are relevant for delivering health services in all countries surveyed, they said.

A "constellation of environmental factors associated with the development process" might be protective or riskier for each disorder, said the researchers. The environmental analysis is the next phase of the research project.