Allergy today magazine > Archived articles > asthma hits plateau but eczema and hay fever increase
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From the Summer 2006/2007 issue of Allergy Today. For more articles like this, subscribe to Allergy Today, click here. asthma hits plateau but eczema and hay fever increaseChildhood allergies have become more widespread around the globe since 1991, according to the world’s largest epidemiological study. And while the incidence of asthma has actually decreased in some groups, the number of people suffering from eczema and hay fever appears to be on the rise. Between 2002 and 2003, Professor Innes Asher, Department of Paediatrics, Faculty of Medical and Health Sciences, The University of Auckland, New Zealand, and team, repeated a 1991 study called The International Study of Asthma and Allergies in Childhood (ISAAC) designed to assess the global prevalence of asthma, hay fever and eczema. In the study, 193,404 children, aged between 6 and 7, from 37 different countries were monitored for symptoms of asthma, such as wheezing and other allergies. The researchers used feedback from the children’s parents for this study. Another 304,679 children, aged 13-14, from 56 different countries, were surveyed directly with the same questions. The study included children from developing countries, such as Brazil, South Africa and Iran, as well as developed countries, such as the UK, Sweden, Canada and New Zealand. In New Zealand, 10,873 children between the ages of 6 and 7 were studied. It was found that the percentage of children in this age-group suffering from hay fever had increased from 9.5 per cent in 1991 to 11.4 per cent in 2003.The study also showed a small increase in the number of children in this age group with eczema (14.3 per cent in 1991 compared to 15 per cent in 2003). But perhaps surprisingly, the percentage of children with asthma in the same age group dropped from 24.3 per cent in 1991to 21.8 per cent in 2003. A different pattern of results was shown for the 13-14 year old New Zealand age group in the same study. The percentage of hay fever sufferers in this group went from 19.1 per cent to 18 per cent, and there was also less eczema (12-9 per cent compared to 8.8 per cent) and asthma (29.7 per cent to 26.7 per cent). An interesting national difference in results for this teenage group for the two time periods was that there was slightly less asthma in Britain, but slightly more hay fever and eczema. In the US, there was less asthma and eczema, but more hay fever. Internationally, over all the centres studied, it was found that increases in prevalence were twice as common as decreases, and increases were more common in the 6-7 year age group than in the 13-14 year age group. The exception was asthma symptoms in the teenage group, where decreases were more common at high prevalence. For both age groups, although more centres showed increases in all three disorders more often than showing decreases, most centres had a mixed pattern of changes. The changes were greatest for eczema in the younger age group, and for hay fever in both age groups. But Professor Innes Asher noted that in Asia, the Pacific and India, increases in the prevalence of all three disorders occurred more often in both age groups than decreases. These patterns might be due to a greater effect of environmental change in younger people for hay fever and eczema, but not asthma, or a cohort effect, where an environmental change took place at a later date that affected the prevalence in the younger age group, but not the older age group. For example, in northern and eastern Europe, rapid environmental change took place in the 1990s (after the collapse of the communist systems) and is thus more likely to have affected the 6–7 year age group in Phase Three than the 13–14 year age group who were born before these changes occurred. And in developing countries, wheezing does seem to be less related to atopy (the general predisposition to allergic reactions) than does hay fever or eczema. Professor Asher suggested that the factors affecting asthma and allergies might act in different ways for developing compared to developed countries, and that their interaction with socio-economic status might also be important. So the factors that cause variation in prevalence might differ from one location to another and from one age-group to another, and could be related to aspects of lifestyle, dietary habits, microbial exposure, economic status, indoor or outdoor environment, climatic variation, awareness of disease, or management of symptoms. There is likely to be a constellation of environmental factors associated with children’s development that relate to the worldwide changes, including the loss of protective factors and the addition of risk factors, and these might be different for each of the three disorders. These will be explored in the environmental analyses of ISAAC Phase Three. Professor Asher concluded that the data have direct relevance for health-service delivery in the countries included in the study, as well as providing a basis for understanding these disorders. In almost every country in the study, there has been a change in prevalence of one or more of the disorders over time. Although seemingly small increases of 0.5 per cent may seem insignificant, they have substantial public-health implications, especially as they often appear to take place in densely populated areas. Quick facts – what the study showed for New ZealandFor New Zealand children aged between 6-7, these were the changes between 1991 and 2003: • hay fever increased from 9.5 per cent to 11.4 per cent • eczema increased from 14.3 per cent to 15 per cent • asthma decreased from 24.3 per cent to 21.8 per cent In the13-14 year age group: • hay fever decreased from 19.1 per cent to 18 per cent • eczema decreased from 12-9 per cent to 8.8 per cent • asthma decreased from. 29.7 per cent to 26.7 per cent Worldwide time trends in the prevalence of symptoms Prof M Innes Asher MBChB, Stephen Montefort MD, The Lancet 2006; 368: 733-43 |