MedWire News: Around half of asthma cases in the general population are due to atopy, and almost a third of these are due to cat allergy, report US scientists who say that the prevention or reversal of atopy could substantially reduce the burden of asthma.
Atopy, which is defined as a propensity to develop immunoglobulin E antibodies in response to allergen exposure, is a known risk factor for asthma. However, it is not clear how many asthma cases are attributable to atopy.
To investigate further, Darryl Zeldin, from the Research Triangle Park in North Carolina, and colleagues studied data on 12,106 individuals aged 6-59 years from the Third US National Health and Nutrition Examination Survey who were skin tested with 10 allergens. Atopy was diagnosed as a result of at least one positive test, while asthma diagnosis was assessed via a questionnaire.
The prevalence of asthma in the study population was 5.2%. Of the asthma cases, 56.3% were attributable to atopy, with even higher proportions seen among women, individuals in the highest education category versus the lower categories, and among those living in highly populated metropolitan areas versus all other areas.
Before adjustment, each allergen-specific skin test strongly correlated with asthma, at odds ratios ranging from 2.1 to 4.5. Adjustment revealed that only tests for cat, Alternaria, white oak, and perennial rye allergens were independently linked to asthma.
Perennial rye positivity was inversely associated with asthma, while the highest percentage of asthma cases associated with a single positive allergen response was for cat allergen, at 29.3%, the team reports in the Journal of Allergy and Clinical Immunology.
They write: "The results of this study have two implications. First, the population-attributable risk conveys a sense of how much disease can be prevented by eliminating the exposure or blocking its effects... Second, this study's results highlight the need for research into nonatopic causes of asthma because a third to half of the asthma cases apparently have a nonatopic etiology."
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