Asthma and lower airway disease
Nonlinear relationship of mite allergen exposure to mite sensitization and asthma in a birth cohort

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Background

There is uncertainty about the nature of the relationship between mite allergen exposure during infancy and the expression of allergic diseases in childhood.

Objective

We sought to explore the relationships between repeated measurements of mite allergen exposure during the first 5 years of life and clinical allergic disease outcomes at age 5 years.

Methods

In a birth cohort of 516 at-risk children, 13 bed dust samples were collected between birth and 5 years of age and analyzed for mite allergen. At age 5 years, the presence of mite atopy was assessed based on skin prick test results, and clinical assessments for asthma, eczema, and wheeze were conducted. The association of allergen exposure with each clinical outcome was examined by means of logistic regression, with adjustments for potential confounders.

Results

The lowest and highest mite exposure quintiles, expressed as mean allergen concentration averaged over 0 to 5 years, were associated with a lower prevalence of mite atopy and of asthma compared with intermediate levels of exposure. These relationships, when determined by using average allergen concentration over 0 to 18 months, were weaker.

Conclusions

This study demonstrates a nonlinear relationship between mite allergen exposure and clinical outcomes in this generally high mite allergen environment.

Section snippets

Subjects

The study population in the Childhood Asthma Prevention Study has been previously described.24, 25 It comprised 616 children who were randomized at birth into active or control groups for both HDM avoidance and dietary intervention. All subjects were classified as being at risk of asthma on the basis of having at least 1 parent or sibling with symptoms of asthma, as assessed by means of a screening questionnaire. The active HDM intervention included the application of an allergen-impermeable

Results

A wide range of values for allergen exposure were observed across the study population over time. A total of 6833 reservoir dust samples were analyzed; 3355 during the period from 0 to 18 months, 1534 from 2 to 3 years, and 1944 from 3.5 to 5 years. Mite allergen was detected in 97% of samples. Little difference was seen in the overall distribution of mean allergen concentration for the 3 periods of the study (see Fig E1 in the Online Repository at www.jacionline.org). For birth to 18 months,

Discussion

The most striking feature of this cohort study is that children in the highest quintile of exposure were significantly less likely to have both mite sensitization and asthma compared with children in the fourth quintile of exposure, suggesting that very high mite exposure might be protective for these outcomes. Additionally, children in the lowest exposure quintile were also less likely to have asthma than those in the fourth exposure quintile. These associations were observed when the exposure

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    Supported by the National Health and Medical Research Council of Australia, the Cooperative Research Centre for Asthma, the New South Wales Department of Health, and the Children's Hospital at Westmead, New South Wales, Australia. Catarina Almqvist was funded by the Swedish Heart Lung Foundation and the Swedish Society of Medicine.

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

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