Early Allergen Exposure Cuts Wheeze Risk
The URECA cohort has been followed since birth, with researchers regularly collecting samples of house dust from their homes.
Early exposure to microbes on farms has been linked to protection against asthma and other allergic disease, but it’s not known if there’s something similar at play in the urban environment, they noted.
It’s also known that both the prevalence and severity of asthma are high in children in poor urban neighborhoods, where conditions that promote allergic sensitization and recurrent wheezing include “stress, lack of biodiversity, and exposure to indoor pollutants and perennial allergens,” Wood and colleagues wrote.
In non-atopic children, the wheezing often goes away, but recurrent wheezing is a known risk factor for asthma in those who have allergic sensitization or other signs of atopy in their preschool years, they added.
Between 35% and 50% of children have some form of wheezing illness — an important cause of outpatient visits and hospital admissions — by the time they are 3, the researchers noted.
The goal is to understand the environmental factors associated with recurrent wheezing — and eventually full-blown asthma — among children growing up in the inner cities, Wood said.
In the so-called Urban Environment and Childhood Asthma (URECA) study, Wood and colleagues are tracking 560 children in the inner-city regions of Baltimore, Boston, New York, and St. Louis.
“There are lots of children who wheeze in the first 3 years of life who don’t go on to have asthma,” he said. Whether the association with recurrent wheezing will be paralleled by a link to asthma won’t be clear until the children start school, he said.
But Wood cautioned that the study looked mainly at recurrent wheezing, rather than frank asthma.
“The surprising finding here was that high exposure to those allergens was actually quite protective,” Wood said.
In previous research into inner-city children with asthma, he said, “we found that one of the major factors that seems to drive their disease is exposure to some allergens that are especially relevant to the inner city,” such as those linked to mice and cockroaches.
The finding, appearing in the Journal of Allergy and Clinical Immunology, was unexpected, Wood told MedPage Today.
But surprisingly, exposure to some allergens and microbes in the first year of life appeared to have a protective effect, according to Robert Wood, MD, of Johns Hopkins University, and colleagues.
A new study confirmed that when inner-city kids were exposed to allergens they had an increased risk of recurrent wheezing and sensitivity to allergens, researchers said.
The full cohort was evaluated when the children were 3 to test the notion that high exposures to allergens, such as those associated with cockroaches and mice, are linked to allergic sensitization and recurrent wheezing.
Within the cohort, Wood and colleagues conducted a nested case control study to see if early life exposure to microbes in the house dust was also linked to allergic sensitization and wheezing.
Specifically, they annually measured allergen-specific IgE for milk, egg, peanut, and German cockroach. When the children were 2 and 3, they also looked for specific IgE for dust mites, dog, cat, mouse, and Alternaria, a fungal genus.
And, when children were 33 months old, the researchers performed skin prick testing for 14 common indoor and outdoor allergens.
- 44% of children for whom complete data were available were sensitized to at least one aeroallergen, 36% had recurrent wheeze, and 9% had eczema.
- 12% met the criteria of the modified asthma predictive index, indicating a high risk for subsequent asthma.
- Cumulative exposure over 3 years to cockroaches, mice, and dust mites was positively associated with sensitization to the allergens when children were 3, with odds ratios ranging from 1.27 to 1.68.
- In contrast, exposure in the first year had little or no association with sensitization to allergens when children were 3.
- And first year exposure to cockroach, mouse, and cat allergens was significantly and inversely associated with recurrent wheeze at age 3, with odds ratios of 0.60, 0.65, and 0.75, respectively.
In the case-control study, involving 104 children, the researchers found a parallel protective effect for some bacteria in house dust, again when exposure was in the first year of life.
The children involved turned out to be roughly evenly divided at age 3 into four categories, those with wheeze alone, atopy alone, both, or neither.
Wood and colleagues found that differences in house-dust bacterial content in the first year were associated with atopy and atopic wheeze.
Relative bacterial richness — the number of bacterial types in each sample, was significantly different (at P<0.02) among the groups and was lower in first-year dust samples from the groups with atopy and atopy/wheeze, compared with children who had neither.
Finally, Wood and colleagues found, children without atopy or wheeze were more likely to have been exposed to high levels of both allergens and microbes in the first year of life.
The study had support from the National Institute of Allergy and Infectious Diseases and the National Center for Research Resources. The authors made no disclosures.