Relevance of allergens from cats and dogs to asthma in the northernmost province of Sweden: Schools as a major site of exposure,☆☆,

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Abstract

Background: The prevalence of asthma in the northernmost region of Sweden has been estimated at 6% to 8% in spite of the very dry climate. The causes of the increase in asthma are not clear, but conditions are unfavorable for dust mite growth, and domestic animals are thought to be the primary source of indoor allergens. Objectives: We sought to investigate the relationship between asthma, exposure, and sensitization in Northern Sweden, with a focus on the role of schools. Methods: Serum was collected from 110 asthmatic children, 55 children with symptoms of asthma but no established diagnosis, and 63 control children (age, 7 and 8 years). Total IgE and specific IgE to 7 allergens were measured. Dust samples were collected from the classrooms of 7- and 8-year-old children in 22 schools from Kiruna and Luleå, Sweden. For comparison, dust was also collected from 24 homes in Kiruna and 2 schools in Virginia in the United States. Results: Serum IgE antibody assays on 165 children with respiratory symptoms confirmed that there was a high degree of sensitization to cat, dog, and birch in Northern Sweden. Cat and dog allergens were present in almost all of the school samples in Sweden. By contrast, dust mite and cockroach allergens were generally unmeasurable. The highest levels of cat and dog allergens were found in samples from desks and chairs. Cat and dog allergen levels in the schools were comparable with but higher than those in the homes without pets. The schools in Virginia had similar allergen levels, except that samples from this humid region also had significant mite allergen. Conclusions: In this climate the primary sensitization associated with asthma is to cat dander and dog dander but also to birch pollen. Mite and cockroach allergens were not present in the dust samples, and sensitization to these allergens was not significant. The schools appear to be a major site of exposure to cat and dog allergens. These results are relevant both to an understanding of the reasons for the increase in asthma in this region and to any proposal to reduce exposure to allergens. (J Allergy Clin Immunol 1999;103:1018-24.)

Section snippets

Study populations

The children studied here were participants in a longitudinal study of all the students from the 3 municipalities of Kiruna, Luleå, and Piteå who were enrolled in grades 1 and 2 (ages, 7 and 8 years) in 1996. Of the children invited, 3431 (97%) participated in the study.2 The schools investigated were those in Kiruna and Luleå. Located inland, Kiruna is a 20,000 square kilometer town of 26,000 inhabitants (as of 1996) 200 km north of the Arctic Circle (latitude, 68° north). The average yearly

RESULTS

Serum IgE antibody assays confirmed that there was a high degree of sensitization to cat, dog, and birch allergens in Northern Sweden (Table I).In contrast, sensitization to dust mite, cockroach, Alternaria spp, and Aspergillus spp was much less common. There was a significant association with asthma for sensitization to animal dander and birch allergens. Among this cohort, the presence of a cat at home has not been found to be a risk factor for either asthma or positive skin test responses to

DISCUSSION

The assays for serum IgE reported here have confirmed that the symptomatic children in Norrbotten were primarily sensitized to cat, dog, and birch allergens. The complete absence of dust mite allergen in schools and houses is in keeping with the results for sensitization and presumably reflects the very low humidity. As expected from visual reports, very little cockroach allergen was detected, and IgE antibodies to Blatella germanica were present in only 3% of the sera. The negative results for

Acknowledgements

We thank the staff and school boards in Kiruna and Luleå, Sweden, and Charlottesville and Albemarle County, Virginia; Lena Gustafsson and Kerstin Kemi-Björnström for their assistance with dust collection; and Pharmacia for providing CAP reagents.

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    Supported by National Institutes of Health grants AI-20565, AI-34607, and the Swedish Asthma-Allergy Foundation.

    ☆☆

    Reprint requests: Thomas A. E. Platts-Mills, MD, PhD, UVa Asthma and Allergic Disease Center, Box 225, Health Science Center, Charlottesville, VA 22908.

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