The 8-year follow-up of the PIAMA intervention study assessing the effect of mite-impermeable mattress covers.

BACKGROUND: Exposure to high levels of house dust mite (HDM) allergens is associated with the development of allergic sensitization to HDM, a risk factor for the development of asthma, rhinitis, and allergic dermatitis. We studied the effect of an early intervention with mite-impermeable mattress covers on HDM allergen levels and the development of asthma and mite allergy throughout the first 8 years of life. METHODS: High-risk children (allergic mother) were prenatally recruited and randomly allocated to two groups receiving mite allergen-impermeable (n = 416) and placebo mattress covers (n = 394) or no intervention (n = 472). Asthma and allergies were assessed yearly by questionnaire. Specific immunoglobulin E and bronchial hyper-responsiveness were measured at the age of 8 years. Mattress dust samples collected at different time points were analyzed for HDM allergens. RESULTS: At the age of 8 years, levels of HDM allergen Der f1 but not Der p1 were lower in the active than the placebo mattress cover group. In repeated measures analyses, we found a temporary decreased risk of asthma symptoms at the age of 2 years in the intervention group compared to the placebo group and a temporary association between higher HDM allergen exposure at the age of 3 months and more asthma symptoms. CONCLUSION: Early intervention with mite-impermeable mattress covers is successful in reducing exposure to Der f1; it only temporarily reduces the risk of asthma symptoms and does not reduce the risk of hay fever, eczema, and allergic sensitization.

Repeated measurements of mite and pet allergen levels in house dust over a time period of 8 years.

BACKGROUND: Studies of the association between indoor allergen exposure and the development of allergic diseases have often measured allergen exposure at one point in time. OBJECTIVE: We investigated the variability of house dust mite (Der p 1, Der f 1) and cat (Fel d 1) allergen in Dutch homes over a period of 8 years. METHODS: Data were obtained in the Dutch PIAMA birth cohort study. Dust from the child's mattress, the parents' mattress and the living room floor was collected at four points in time, when the child was 3 months, 4, 6 and 8 years old. Dust samples were analysed for Der p 1, Der f 1 and Fel d 1 by sandwich enzyme immuno assay. RESULTS: Mite allergen concentrations for the child's mattress, the parents' mattress and the living room floor were moderately correlated between time-points. Agreement was better for cat allergen. For Der p 1 and Der f 1 on the child's mattress, the within-home variance was close to or smaller than the between-home variance in most cases. For Fel d 1, the within-home variance was almost always smaller than the between-home variance. Results were similar for allergen levels expressed per gram of dust and allergen levels expressed per square metre of the sampled surface. Variance ratios were smaller when samples were taken at shorter time intervals than at longer time intervals. CONCLUSION: Over a period of 4 years, mite and cat allergens measured in house dust are sufficiently stable to use single measurements with confidence in epidemiological studies. The within-home variance was larger when samples were taken 8 years apart so that over such long periods, repetition of sampling is recommended.