Mechanisms of Allergy
Four-year incidence of allergic sensitization among schoolchildren in a community where allergy to cat and dog dominates sensitization: Report from the obstructive lung disease in northern sweden study group

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Abstract

Background

Exposure to high levels of cat allergen might prevent sensitization.

Objective

We sought to measure the incidence of allergic sensitization among schoolchildren living in a dust mite– and cockroach-free environment and the associated risk factors.

Methods

In 1996, a longitudinal cohort was established in northern Sweden, including 2454 children aged 7 to 8 years. Children were skin tested, and the testing was repeated 4 years later. Questionnaires were completed yearly. Participation was 88% both in 1996 and 2000.

Results

The prevalence of positive skin test results increased from 20.6% at age 7 and 8 years to 30.4% at age 11 and 12 years, a cumulative incidence of 13.8%, and was significantly higher among boys. The incidence was highest for cat (6.0%), timothy grass (5.9%), dog (4.9%), and birch (3.6%). A family history of allergy was the major risk factor for both a positive skin test response at age 7 and 8 years (odds ratio [OR], 1.69; 95% CI, 1.36-2.10) and for development of a positive skin test response over the next 4 years (OR, 1.67; 95% CI, 1.23-2.28). A significant inverse association between cat and dog ownership and the prevalence of type 1 allergy was found, particularly for those children who had lived with a cat both before age 7 and 8 years and during the next 4 years (OR, 0.44; 95% CI, 0.31-0.61). A similar pattern, although not significant, was found for incident cases.

Conclusion

The high incidence of type 1 allergy at this age was similar to reports from communities with mite and cockroach allergen. Despite cat and dog being the most common allergens of sensitization, keeping these animals at home was not associated with an increased risk for sensitization.

Section snippets

Methods

We used questionnaires and skin prick tests (SPTs). SPTs were performed at the beginning of the study and 4 years later. A questionnaire was completed yearly. Consent for SPTs was obtained from parents. The ethical committee at the University Hospital of Northern Sweden in Umeå approved the study.

Prevalence and incidence

The prevalence of a positive SPT response to any of the tested allergens was 20.6% at age 7 and 8 years and had increased to 30.4% by age 11 and 12 years. At both ages, the most common allergen was cat, followed by dog, birch, and timothy grass (Fig 2). The prevalence of any positive SPT response at age 11 and 12 years among the 1870 children who were tested twice was 30.8%.

The cumulative incidence of any positive SPT response during the 4-year period was 13.8% among the 1478 children with a

Discussion

The incidence of sensitization to inhalant allergens over 4 years was high (13.8%) and resulted in an increase in prevalence from 20.6% at age 7 and 8 years to 30.4% 4 years later. The high incidence combined with the prospective nature of the study design and the size of the cohort allowed for an in-depth analysis of the risk factors for the onset of sensitization. The high participation rate, standardized methods, and close correlation between SPT results and in vitro IgE assays at age 7 and

Acknowledgements

We thank Kerstin Kemi-Björnström, Lena Gustafsson, and Aina Johnsson for collection of the data. ALK and Pharmacia-Upjohn are acknowledged for help with providing test material and GlaxoSmithKline and AstraZeneca for additional support.

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    Supported by the Swedish Heart-Lung Foundation, the Swedish Foundation for Health Care Science and Allergy Research (Vårdal), the US National Institute of Allergy and Infectious Diseases (AI-20565 and AI-34607), the Swedish Asthma-Allergy Foundation, and Norrbotten's local health authorities.

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