May 18, 2012

Is Atopy Per Se a Risk Factor for Having Atopic Diseases?

Taking the former proposal to consider longitudinal studies, to elucidate the attributable risk of different exposures, a cohort of more than 1,000 children was evaluated by their atopic status, and related to asthma, rhinitis, and eczema. Sensitization to dust mites was the strongest independent risk factor for having asthma  to grass pollen for having rhinitis  and to peanut for having eczema. Even though less than half of the original cohort was skin tested at the age of 4, some relevant tendencies were evident: the prevalence and severity of asthma correlated with allergen sensitization, the risk of all allergic diseases increased with the number of positive prick tests, there was a predominance of male sex at this age, but they conclude that only 30–40% of allergic diseases is attributable to atopy, and the rest to the affected organ or other factors. A recent report suggests that asthma attributable to atopy could vary depending on allergen exposure and its modifications because of the environment such as climate.

But atopy alone does not explain much of the real life, where multiple factors could influence the development of atopic diseases, such as respiratory viral infections and the development of asthma. In a cohort of more than 2,000 children, where the presence of current asthma at 6 years of life was correlated with atopy and respiratory tract infections in first year, concluded that both conditions were independently associated with a significant risk of having asthma by the age of 6. Also, maternal feeding evidences a protective behavior.

Another longitudinal study demonstrated the association of infantile chest infections with wheezing and asthma, and the importance of early life atopic status for the presence of wheezing, asthma, and bronchial hyper-responsiveness at 10 years of life. Other conditions such as familiar asthma, early passive smoking, and having eczema at the age of 4 were also significantly associated with asthma and wheezing but not with bronchial sensitivity.
We must preliminary conclude that atopy per se is not enough, neither to express atopic diseases nor to justify the increased incidence of them.

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