Low domestic exposure to house dust mite allergens (Der p 1) is associated with a reduced non-specific bronchial hyper-responsiveness in mite-sensitized asthmatic subjects under optimal drug treatment

Airway inflammation in asthma causes symptoms, airflow limitation and bronchial hyper-responsiveness. The strategy of asthma management is to reduce airway inflammation by drug treatment and avoidance of triggers, including allergens. We determined the effect of exposure to house dust mite (HDM) allergens on bronchial responsiveness in asthmatics sensitive to mites while under optimal drug treatment. We studied 71 mild to moderate HDM-sensitive asthmatics. Drug treatment sufficient to keep asthma under control was administered to each patient for 1 year. Subjects were divided into two groups, according to the amount of Der p 1 in their bedrooms measured after standard HDM reduction measures: low Der p 1 exposure (0.64 +/- 0.5 microg/g dust) (Group 1, n = 34) and high Der p 1 exposure (12.5 +/- 11.4 microg/g) (Group 2, n = 37). Bronchial responsiveness to methacholine (PD20FEV1) was determined at the beginning and end of the study. In Group 1, PD20FEV1 increased 2.15-fold at the end of the study from 57 to 123 microg (P < 0.05), whereas in Group 2 no significant changes were observed. The subjects in Group 2 tended to increase the use of inhaled steroids and bronchodilators in the autumn months compared with subjects in Group 1, but the difference was not significant. This long-term study shows that exposure to lower levels of mite allergens in the bedroom is associated with a decrease of bronchial hyper-responsiveness in sensitized asthmatic subjects under optimal drug treatment