The aim of the study was to describe the distribution of house-dust mite (HDM) allergens in homes of three-year-old children and to test the hypothesis whether the content of HDM allergens exceeding 2 microg/g of dust may be regarded as a risk level possibly affecting respiratory health in early childhood.
House-dust samples were collected in 275 dwellings from mattresses, children's bedrooms and kitchen floors. In the laboratory, dust samples were analyzed for Der f 1 and Der p 1 using monoclonal antibody enzyme-linked immunosorbent assays (ELISA). At the time of the house-dust collection, mothers were interviewed on the household characteristics and their children's respiratory health. Respiratory outcome variables included wheezing or whistling in the chest irrespective of respiratory infections. The number of the wheezing episodes and their duration in days over the last 6 months were recorded in the questionnaire. In the multivariate Poisson regression analysis on the association between the occurrence of wheezing and exposure, a set of potential confounders, such as child's gender, maternal education, maternal allergy, older siblings, presence of moulds, house dampness, and environmental tobacco smoke (ETS) was taken into account.
The adjusted incidence rate ratios (IRR) of wheezing ascribed to a higher HDM level (> 2.0 microg/g dust) were 1.84 (95% CI: 1.45-2.34) for duration of wheezing and 1.56 (95% CI: 0.88-2.75) for episodes. Of the confounders taken into consideration, the presence of moulds had the strongest impact on the risk of wheezing (IRR = 4.24; 95% CI: 3.08-5.84).
The data support the view that exposure to a higher level of HDM allergens increases the burden of respiratory diseases in the early childhood and the effect is independent of maternal atopy, ETS, and moulds in homes.