Nonlinear relations between house dust mite allergen levels and mite sensitization in farm and nonfarm children

Background: Low sensitization rates to common allergens have been observed in farm children, which might be due to high exposure to microbial agents. It is not known how microbial agents modify the association between specific allergen exposure and sensitization. Objective: To examine the relations between house dust mite allergen exposure and mite sensitization in farm and nonfarm children and to assess the effects of microbial agents levels on this association. Methods: Major mite allergens of Dermatophagoides pteronyssinus (Der p 1) and Dermatophagoides farinae (Der f 1), endotoxin, beta(1,3)-glucans and fungal extracellular polysaccharides were measured in mattress dust of 402 children participating in a cross-sectional study in five European countries. Mite allergen (Der p 1 + Der f 1) levels were divided into tertiles with cut-offs 1.4 and 10.4 mu g/g. Sensitization was assessed by measurement of allergen-specific immunoglobulin E against house dust mite. Results: Prevalence ratios of mite sensitization for medium and high when compared with low mite allergen levels were 3.1 [1.7-5.7] and 1.4 [0.7-2.8] respectively. Highest mite sensitization rates at intermediate exposure levels were consistently observed across country (except for Sweden) and in both farm and nonfarm children. The shape of the dose-response curve was similar for above and below median mattress microbial agent levels, but the 'sensitization peak' appeared to be lower for above median levels. Conclusions: Our data suggest a bell-shaped dose-response relationship between mite allergen exposure and sensitization to mite allergens. In populations with high microbial agent levels and low sensitization rates, the curve is shifted down.