Preventing Severe Asthma Exacerbations in Children: A Randomized Trial of Mite-Impermeable Bedcovers

PURPOSE OF THE STUDY. Mite-proof mattress and pillow encasings are commonly recommended for children with asthma who are allergic to dust mites. Do they work? STUDY POPULATION. This study included 284 children aged 3 to 17 years with physician-diagnosed asthma who presented to the emergency department (ED) with an asthma exacerbation and who has a positive skin test to house dust mite. METHODS. Subjects were randomly assigned to receive active (ie, mite-proof) encasings or placebo encasings on the pillow, mattress, and duvet of all beds in the child’s bedroom. No additional dust mite avoidance information was provided. Placebo encasings were custom manufactured to match the active encasings. Der p 1 levels were measured in vacuumed dust samples from the bed and floor at baseline and 12 months. Interviewers (masked to group assignment) conducted telephone interviews with the primary caregiver at 1, 4, 8, and 12 months regarding asthma exacerbations, unscheduled medical care, and medication use, including oral corticosteroids (OCSs). Outcome measures included ED visits because of asthma requiring OCSs and all OCS courses regardless of whether they were associated with an ED visit. RESULTS. Mattress Der p 1 levels decreased by 84% with mite-proof covers, whereas there was no decrease with placebo covers. There was no change in floor Der p 1 levels in either group. At 12 months, significantly fewer children in the active group than in the placebo group had an ED visit with an asthma exacerbation (36 [29.3%] of 123 vs 49 [41.5%] of 118; P = .047). In a multivariable analysis, the risk of an asthma ED visit was 45% lower in the active group (hazard ratio, 0.55; 95% confidence interval, 0.36–0.85; P = .006) than in the placebo group. There was, however, no difference between the groups in the risk of OCS use for exacerbations (hazard ratio, 0.82; 95% confidence interval, 0.58–1.17; P = .28). CONCLUSIONS. Mite-impermeable encasings were effective in reducing asthma ED visits for children sensitized to dust mites, but there was no effect on the need for treatment with oral prednisolone. This allergen-avoidance measure may reduce the health care burden for children with asthma who have a concomitant dust mite allergy. REVIEWER COMMENTS. Although this single environmental control measure did not reduce the number of exacerbations requiring OCSs, it did reduce the number of exacerbations requiring ED visits and may have been even more effective if additional dust mite