First-Year Allergen Exposures May Reduce Later Risks

Larry Hand

June 11, 2014

Exposure during the first year of life to specific allergens and bacteria, surprisingly, may reduce recurrent wheeze and thwart genetically predisposed allergic disease or asthma, according to an article published online June 4 in the Journal of Allergy and Clinical Immunology.

Susan V. Lynch, PhD, associate professor of medicine at the University of California, San Francisco, and colleagues evaluated the outcomes of 3-year-olds in the Urban Environment and Childhood Asthma (URECA) study who were born in Baltimore, Maryland; Boston, Massachusetts; New York City; or St. Louis, Missouri.

URECA is a longitudinal birth cohort study to examine the effects of environmental exposures on children born to poor urban parents, at least 1 of whom has an allergic disease or asthma. Researchers recruited 560 families from urban areas with more than 20% of the residents below the poverty line between February 2005 and March 2007.

The new report is the evaluation of exposure to sensitizing allergens — cockroach and mouse, in particular — on the entire cohort at 3 years of age. During the process of this investigation, the researchers also conducted a nested case-control study on whether early-life exposure to microbes in house dust in the children's homes leads to development of allergy and wheezing.

Among 467 children with enough data to assess recurrent wheeze at age 3 years, 44% experienced sensitization to at least 1 aeroallergen, 36% had recurrent wheeze, and 9% had eczema. Factors that increased the risk for recurrent wheeze included lower birth weight and gestational age, the number of smokers in the household, and household income below $15,000.

Children with recurrent wheeze experienced a median of 6 episodes by age 3 years. Their prescription medicines included albuterol (77%), inhaled corticosteroid (27%), and oral corticosteroid (33%).

Cumulative exposure over the course of 3 years to cockroach, mouse, and dust mite increased the risk for sensitization to the allergens (odds ratio [OR], 1.27 - 1.68), but the researchers found little or no association between exposures during the first year and sensitization at age 3 years.

"[I]n contrast to our expectations, significant inverse relationships were found between first-year exposure to cockroach, mouse, and cat, but not house dust mite or dog, allergens and recurrent wheeze at age 3 years," the researchers write (OR, 0.60, 0.65, 0.75, 0.97, and 1.01, respectively; P ≤ .01)

For the nested study into microbes in house dust, the researchers looked at dust samples from 104 URECA homes, collected from mattresses and floors in children's bedrooms and family room floors and furniture. They found similar results for these 104 children as in the full cohort.

"To our knowledge, this is the first scientific report of exposure to high levels of allergens combined with an environment rich in specific bacterial families as having a protective effect against atopy and atopy with wheezing in early childhood," the researchers write.

Unexpected Findings

"We went into this with the opposite hypothesis, that exposure to things like cockroach and mouse, which are certainly bad in the inner city for asthma once you have asthma, would be things that would likely be associated with developing asthma," corresponding author Robert A. Wood, MD, chief of the Division of Allergy and Immunology at the Johns Hopkins Children's Center in Baltimore, Maryland, told Medscape Medical News. "To find that they actually appear to be protective was not at all expected."

But do not change clinical practice yet, he advises.

"People want to know, can you apply this to your clinical practice, and the answer is no. We think the more we learn about these relationships, the more chance there is [that] eventually some preventative strategies can be developed. But there's nothing we can take from this study and bring it into the clinic and talk to a family," he said.

"The most important thing will be to follow these kids to an age where we can say whether or not they have asthma. We were careful not to use the word asthma too much in this study because there are lots of children in the first 3 years who have recurrent wheezing but don't go on to asthma. And some who don't wheeze in the first 3 years will have asthma," he explained.

"The biggest question is how these findings hold up over the course of the next several years. Our next big time point is age 7, when we can make a definitive diagnosis of asthma," he continued. "Whether these relationships are transient or persistent is the next big step."

This research was supported by the National Institute of Allergy and Infectious Diseases and the National Center for Advancing Translational Sciences. Dr. Lynch has reported receiving research support from the National Institute of Allergy and Infectious Diseases, serving as a board member for Second Genome, receiving consultancy fees from Jannsen and Regeneron, receiving lecture fees from 3 organizations, owning a patent with and receiving royalties from KaloBios, and receiving payment for development of educational presentations from Georgia Regents University. Dr. Wood has reported receiving research support from the National Institutes of Health, receiving consultancy fees from the Asthma and Allergy Foundation of America, and receiving royalties for UpToDate. Complete conflict-of-interest information for other co-authors is available in the article.

J Allerg Clin Immunol. Published online June 4, 2014. Full text


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