Sensitization to house dust mites in different climatic areas

With the use of local meteorologic data, the mean monthly indoor relative humidity (RH) was calculated for the area of residence of each of 774 children with respiratory symptoms who were referred to our allergy clinic. Seven hundred fourteen children lived in areas in which the mean indoor RH was 50% or more for 4 or more mo per year ("humid" areas), and 60 children lived where this RH was present for no more than 2 mo per year ("dry" areas). Of those children from the "humid" areas, the skin prick test was positive to Dermatophagoides farinae in 31% and D. pteronyssinus in 40%, whereas in those children from "dry" areas, tests were positive in 3% and 2%, respectively, (p less than 0.001). There was also a marked difference in the degree of sensitivity. In those children with a positive RAST (more than 12% of binding relative to allergen-specific pooled reference sera), the mean level of binding was 51% +/- 3.5% for D. farinae and 62% +/- 4.4% for D. pteronyssinus in children from "humid" areas but never exceeded 14% for either species in those children from "dry" areas (p less than 0.001). Sensitivity to D. farinae and D. pteronyssinus is frequent in "humid" areas and seldom, if it is ever, occurs in areas that are "dry," either as a result of a semiarid climate or a prolonged heating season. These findings have implications for the etiologic diagnosis and specific treatment of atopic patients living in different climatic regions.