Asthma seasonal variation associated with allergic sensitization
medwireNews: Seasonal variation in asthma attacks in young adults is dependent on their sensitization to outdoor allergens, a study shows.
Reporting on information collected from 2637 asthma sufferers across 16 countries between 1991 and 1993, Deborah Jarvis (Imperial College, London, UK) and colleagues say: "Most young adults with asthma reported periods of the year when their asthma attacks were more common."
Each participating study center sent out postal questionnaires to a population of adults aged between 22 and 44 years. A random sample of those who responded, plus a sample of those with symptoms suggestive of asthma, were then invited for further tests.
The questionnaire asked responders with asthma to identify which months of the year (divided into bimonthly periods) they usually suffered attacks. Participants were then given skin-prick tests to various outdoor and indoor allergens, including grass, birch, Alternaria, house dust mite, and cat, and blood samples were taken to test for serum immunoglobulin (Ig)E levels.
Skin-prick tests were considered positive if the mean wheal diameter was greater than 0 mm, and allergen sensitization was considered to be present if specific IgE levels were greater than 0.35 kU/L.
Participants sensitized to indoor allergens were found to have the same seasonal variation patterns as those who were not.
By contrast, asthmatics sensitized to grass, birch and Alternaria were found to have different seasonal patterns than those not sensitized. These patterns were dependant on regional variations in allergen levels. For example, in southern Europe, where Alternaria levels are highest between May and August, those sensitized to the allergen were more likely to report asthma attacks during this period, whereas those in northern Europe reported a higher incidence of asthma in July and August only.
However, writing in the European Respiratory Journal, the authors caution that "because of the relatively small sample size in some centres [we] have grouped information from centres to country level, and then to regional level.
"Our regions are thus defined by geopolitics rather than factors that others may consider more relevant (eg: pollen levels, climate, land usage)."
Asthmatics sensitized to grass were more likely to report attacks during the summer months. This was also true of participants reporting hayfever, but only among those who were found to be grass sensitized.
"Although reporting hayfever identifies those at greater risk of spring/summer asthma exacerbations… the addition of testing for grass sensitisation may be more useful to identify those at risk," suggest Jarvis et al.
They conclude: "This is a timely reminder to clinicians to remain alert to seasonal allergens as a potential trigger to asthma attacks in their sensitised patients."
By Afsaneh Gray, medwireNews Reporter