MIAMI BEACH — Exposure to mouse allergen in the home is a risk factor for asthma morbidity in early childhood, according to the findings of two prospective studies presented at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.
Occupational exposure to mouse allergen is known to contribute to asthma morbidity. But there are no published studies evaluating the role of early mouse allergen exposure in the home in the development of wheezing, asthma, and atopy later in life.
In a study in which dust samples were collected at baseline, 3 months, and 6 months from the bedrooms of 127 preschool children with asthma from inner-city Baltimore, patients were stratified by exposure and sensitization status into four groups at each visit. Higher exposure was defined as a level of mouse allergen of more than 0.5 mcg/g of dust.
Skin testing revealed that 68% of the patients were atopic and 26% were sensitized to mouse, Dr. Elizabeth Matsui and her colleagues at Johns Hopkins University, Baltimore, wrote in a poster. At baseline, there were 8 children (6.3%) in the positive sensitization/lower-exposure group; 25 (19.7%) in the positive sensitization/higher-exposure group; 22 (17.3%) in the negative sensitization/lower-exposure group; and 72 (56.7%) in the negative sensitization/higher-exposure group.
In longitudinal analyses, mouse-sensitized children exposed to higher levels of mouse allergen were three times more likely to have an unscheduled doctor's visit and more than twice as likely to have had an emergency department visit for asthma in the previous 3 months. Nine of the 10 hospitalizations that occurred during the study period were among children in this group.
Exposed and sensitized children also were more likely to report more days of symptoms (odds ratio 1.5), more days of cough (OR 1.6), more nighttime symptoms (OR 1.3), and more use of rescue medications (OR 1.8) in the previous 2 weeks. The findings persisted after adjustment for age, sex, atopy, and cockroach allergen sensitization and exposure.
“Clinicians have to think about skin testing or obtaining RASTs [radioallergosorbent tests] on patients we see in the clinic to determine their mouse sensitization status, and then talk to them about exposure and what they can do,” Dr. Matsui said in an interview. Parents can help reduce exposure by sealing cracks and holes in walls or doors, disposing of all leftover food, and having pest exterminators treat their home.
In a second poster presented at the meeting, the Home Allergens and Asthma Study—a prospective birth cohort study of children in metropolitan Boston—followed 505 infants from 498 families with a history of asthma or atopy. House dust samples collected when children were age 2 months and 3 months were analyzed for mouse urinary protein. Skin testing or allergen-specific IgE testing was performed at age 7 years.
After adjustment for sex, household income, and other confounding factors, multivariate analysis revealed that infants who were exposed to mouse allergen had twice the odds of developing any atopy by age 7, Dr. Wanda Phipatanakul and colleagues at Harvard Medical School, Boston, wrote. Increasing levels of mouse allergen exposure didn't substantially increase the risk of developing recurrent wheezing, asthma, allergic rhinitis, or eczema later on.
Infants with detectable mouse allergen exposure at 2–3 months also had an increased risk of wheezing in early life, but this effect was not significant by age 7. “We think that the effect attenuates over time,” Dr. Phipatanakul said in an interview.
Although mouse allergen exposure is considered an inner-city problem, the cohort included suburban households, suggesting that clinicians consider mouse allergen exposure when evaluating any child for asthma. A national study showed that 82% of American homes had detectable levels of mouse allergens (J. Allergy Clin. Immunol. 2004;113:1167–71).