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Little Rock, AR
ABSTRACT
PURPOSE OF THE STUDY.: To determine to what extent allergen exposure in infancy (3 months old) leads to sensitization, wheeze, and physician-diagnosed asthma at 4 years of age.
STUDY POPULATION.: This study is of a subsample of a prospective birth cohort (n = 4146 children) recruited in the Netherlands. Subjects were children (n = 1127) classified as high risk (n = 464, atopic mother) and low risk (n = 663, nonatopic mother).
METHODS.: Mothers were identified during pregnancy as atopic or nonatopic using a validated screening questionnaire on asthma and inhalant allergies. Children were recruited on the basis of high-risk (atopic mothers) and low-risk (nonatopic mothers) for close follow-up including a home visit at 3 months of age and a medical examination at 4 years of age. At the home visit, dust samples were collected from the child’s mattress and analyzed for house dust mite (Der p 1), cat (Fel d 1), and dog (Can f 1) with samples adjusted for season of collection. At 4 years of age, blood samples were drawn for specific IgE levels to inhalant allergens. Data on demographic factors, respiratory symptoms, and risk factors for asthma were collected by yearly questionnaires. Participants were assessed and placed into a diagnostic category: never wheeze, early transient wheeze (at least 1 episode of wheeze within 3 years of life and no wheeze during fourth year), late-onset wheeze (no wheeze in first 3 years of life and at least 1 in fourth year), persistent wheeze (1 episode of wheeze in the first 3 years of life and at least 1 episode in the fourth year), and physician-diagnosed asthma.
RESULTS.: Allergen sensitization was noted to dust mite, cat, or dog allergens in 14%, 7%, and 4%, respectively. Transient wheeze was noted among 24% and persistent wheeze among 11% of participants, with 4% having physician-diagnosed asthma at 4 years. Allergen exposure was less than detection limits for 42%, 13%, and 68% to Der p 1, Fel d 1, and Can f 1, respectively, with no significant differences between the children of nonatopic and atopic mothers. Of those with allergen exposure, only exposure to house dust mite and cat allergen were found to increase the risk of sensitization at 4 years (odds ratio: 3.22, P = .01; and odds ratio: 2.60, P = .06, respectively). Exposure to allergens was not found to be significantly associated with early transient wheeze. There was an association between cat allergen and persistent wheeze (odds ratio: 2.22; P = .11). In children of atopic mothers, there was a positive association between mite exposure and diagnosed asthma. In children of nonatopic mothers, there was a positive association between dog dander exposure and persistent wheeze. Overall, allergen exposure was not highly associated with physician-diagnosed asthma; however, in children with atopic mothers, dust mite exposure was associated with asthma diagnosis (odds ratio: 3.52; P = .07).
CONCLUSIONS.: The association between allergen exposure and sensitization was demonstrated for dust mite and cat allergens at 4 years. Cat allergen exposure and sensitization were associated with persistent wheeze. Early mite and dog allergen exposure might lead to asthma and persistent wheeze in subgroups defined by maternal atopy.
REVIEWER COMMENTS.: Similar to other longitudinal cohort studies, this study demonstrates an association between allergen exposure and sensitization and provides some additional evidence for the link between allergen exposure and persistent asthma. Long-term follow-up of such cohorts is necessary to help us better understand the relationship between early allergen exposure and development of atopy and asthma.
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