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Impermeable bed covers for asthma and rhinitis: testing conventional wisdom
▸ The increasing prevalence of allergic disease has prompted exploration of new therapies. In 2 similar, placebo-controlled, randomized trials, investigators tested whether dust-mite-impermeable bed covers improve health outcomes in patients with asthma or allergic rhinitis.
In a multicenter U.K. study, 1122 adults (age range, 18-50) with asthma were given either impermeable or permeable covers for their bedding. Despite significantly lower levels of dust-mite allergen in the mattress dust of the impermeable-cover group at 6 months (although not at 12 months), no differences were found between groups in the primary outcomes (peak expiratory flow rate at 6 months, cessation of inhaled corticosteroid treatment, or mean reduction in steroid dose). Analysis that was restricted to the 65% of patients with dust-mite allergy also found no between-group differences.
In a multicenter European trial, 232 children and adults (age range, 8-50; mean age, 26) with allergic rhinitis were assigned to use either impermeable or permeable bed covers. Once again, despite a significant reduction from baseline levels in dust-mite concentration in the bedding of the intervention group (at 12 months), no between-group differences were noted in severity of rhinitis, nasal-allergen provocation test scores, or daily symptom scores. No differences were found in analyses that were restricted to children or to patients with dust-mite allergy.
Comment
▸ The results of these studies are disappointing. Many groups have promoted environmental control for allergic disorders. An editorialist points to 2 kinds of errors that can plague studies of environmental control for allergic disorders: Families assigned to the placebo group might institute other environmental changes that have a greater effect than the studied intervention, and a single environmental intervention is not likely to achieve significant results. Environmental control beyond impermeable bedding should be considered for every patient …