TRANSIENT SENSITIZATION TO HOUSE-DUST MITES - A STUDY ON THE INFLUENCE OF MITE EXPOSURE AND SEX

This study aimed to evaluate the prognosis of a previous positive skin test to house-dust mites (HDM) in relation to environmental exposure. A total of 115 children, 50 from Stockholm and 65 from northern Swede n, all with a previous (average 2.5 years) positive Phazet (Pharmacia AB, Uppsala, Sweden) skin prick test (SPT) to extracts of Dermatophago ides pteronyssinus (Dpt) and/or D. farinae (Df) were included. Dust sa mples were collected from the children's mattresses, and the total (Dp t, Df; and D. microceras [Dm]) amount of major mite allergen was measu red by ELISA (50 children) and expressed as microgram allergen per gra m of dust, or was measured by microscopy (65 children). The results of microscopic mite counts were transformed to approximate allergen leve ls as 2 mu g equals 100 mites per gram of dust. Of 115 originally SPT- positive children, only 48 (48%) remained positive at retest, while th e majority (58%) were SPT negative after 2 years. Among the 67 convert ed children, 11 were still exposed to mite allergen, but only to low c oncentrations (only one converted child being exposed above the sugges ted threshold level [TLV] of 2 mu g/g), compared to 15/48 children sti ll SPT positive who were exposed above the TLV. This shows that contin ued mite exposure is a major risk factor (OR=30, CI 4.8-184) for conti nued positive SPT to HDM. A minor risk factor for continued sensitizat ion was sex, boys having a higher risk than girls (OR=2.2, CI 1.0-4.8) . In conclusion, a surprisingly high rate of SPT conversion occurred, mainly as a result of a favorable indoor environment with low exposure to HDM and, to a lesser degree, as a result of sex. The present resul ts support the view that the risk level of exposure is 2 mu g mite all ergen per gram of dust.