Mouse allergen exposure associates with air trapping in urban children
Published: November 14, 2022
Environmental exposures, including indoor allergens and pollutants, are a significant cause of asthma symptoms and exacerbations in urban children with asthma. Air trapping, a type of obstruction that occurs primarily in the smaller airways, has been associated with more severe and unstable asthma in children. Air trapping occurs when air that would otherwise be exhaled with forced exhalation is retained in the lungs. Recently, investigators have defined air trapping using pre- and post-bronchodilator (BD) spirometry. The causes of air trapping are poorly understood; however, it is plausible that airborne environmental exposures may be implicated in air trapping as these exposures can penetrate down to the smaller airways where air trapping occurs and children with air trapping have been found to have an elevated total allergy antibody, immunoglobulin E.
In this recent study published in The Journal of Allergy and Clinical Immunology (JACI), Grant et al used data from the Environmental Control as Add-on Therapy for Childhood Asthma (ECATCh) study to examine the relationship between environmental exposures and air trapping in urban children with persistent asthma. ECATCh enrolled 155 children ages 5-17 with persistent asthma and randomized them 1:1 to comprehensive environmental control strategies plus controller medication titration vs controller medication titration alone. Allergic sensitization was assessed at baseline, home environmental exposures (cockroach, mouse, dust mite, cat, dog, particulate matter [PM], and air nicotine) were measured at 0, 3, and 6 months with clinical outcomes assessed at 0, 2, 4, and 6 months. There were no outcome differences by group, therefore, groups were combined for the air trapping analyses. Air trapping was defined as a forced vital capacity (FVC) z-score of less than -1.64 or a change in the FVC with bronchodilation of ≥10 % predicted. Airflow limitation was defined as a forced expiratory volume in 1-second (FEV1)/FVC z-score of less than -1.64. A participant could be classified as having: (1) neither air trapping nor airflow limitation, (2) airflow limitation alone, (3) air trapping alone, or (4) both airflow limitation and air trapping. The primary outcome was air trapping, which was defined as the presence of air trapping, with or without airflow limitation. Analyses were performed to evaluate associations between air trapping and indoor exposures.
The study population was primarily Black and on public insurance with a mean age of 10 years. Forty-eight percent of participants had had oral steroids for asthma in the previous 6 months and 25% had been hospitalized for asthma in the previous 12 months. Sixty-six percent of participants were allergic to mouse, 56% to cockroach, and 70% were allergic to ≥2 allergens. Overall, 39 (25%) participants had air trapping at ≥1 visit. Mouse allergen exposure collected from the bedroom floor dust and from the air was associated with an increased odds of air trapping. For each 2-fold increase in bedroom floor mouse allergen concentration, there was an estimated 23% higher odds of having air trapping. Similarly, for each 2-fold increase in airborne mouse allergen concentration, there was an estimated 19% higher odds of having air trapping. Further analyses which divided the participants into mouse allergic and not mouse allergic showed that among those who were allergic to mouse, mouse allergen exposure continued to be associated with an increased odds of air trapping. For those participants not allergic to mouse, the associations between mouse allergen exposure and air trapping were no longer found. There were no associations between other exposures (cockroach, dust mite, cat, dog, PM, and air nicotine) and air trapping. There were also no associations between any exposure and airflow limitation.
In this population of predominately low-income, Black urban children with asthma, increased exposure to mouse allergen was found to be associated with an increased odds of having air trapping. It is possible that the presence of air trapping in the lungs of mouse-allergic children with asthma and high mouse allergen exposure explains some of the excess asthma burden found in low-income, urban populations.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.
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