Background: Mite allergen exposure is essential for the process of specific allergic sensitization. However, it is not clear whether incidence of specific sensitization at school age depends on the level of mite antigen exposure. Therefore the relationship between mite allergen exposure and incidence of specific sensitization was investigated.
Methods: Eighteen hundred twelve primary school children were enrolled in a population-based 2-year follow-up study. In three consecutive skin prick tests (SPTs), each 12 months apart, sensitization to Dermatophagoides pteronyssinus (Dpt) and six non-Dpt allergens was ascertained. To assess exposure to Der p I between the first and second SPTs (period I) and the second and third SPTs (period II), the amount of antigen per gram of dust (taken from the children's mattresses was measured. By using the SPT reactions to Dpt as a basis, conversions after "no wheal" were classified as doubtful incidence (average yearly incidence = 6.7%) or definite incidence (average yearly incidence = 3.2%). Then, with the use of multiple logistic regression, the risk of exposure to Der p I (medians: 1.4 micrograms/gm in period I, 1.6 micrograms/gm in period II) was analyzed with adjustment being made for gender, low gestational age, parental atopy, and initial sensitization to non-Dpt allergens.
Results: Regarding doubtful incidence, the analysis failed to identify a reliable cutoff point of exposure. For definite incidence, the Der p I exposure represents a significant risk in the total population, starting from a concentration of 9 micrograms/gm. This effect is modified by an initial sensitization to non-Dpt allergens: for these children exposure to concentrations above 2 micrograms/gm poses a significant risk, whereas for the population without other initial sensitizations, only an extremely high cutoff limit (> 80 micrograms/gm) gains significance.
Conclusion: Our data suggest that a concentration limit of 2 micrograms Der p I antigen per gram of dust should be regarded as minimal avoidance level for primary prevention in children with sensitization to other inhalant allergens.