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Impermeable Bed Covers for Asthma and Rhinitis: Testing the Conventional Wisdom

So far, reducing dust mite allergens in bedding does not demonstrably improve symptoms.

The increasing prevalence of allergic disease has prompted exploration of new therapies. In two 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, there were no differences between groups in the primary outcomes (peak expiratory flow rate at 6 months, cessation of inhaled cortical steroid treatment, or mean reduction in steroid dose). An analysis 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 years; mean age, 26 years) with allergic rhinitis were assigned to use of 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, there were no between-group differences in the severity of rhinitis, nasal-allergen provocation test scores, or daily symptom scores. No differences were found in analyses 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 two kinds of errors that can plague studies of environmental control for allergic disorders: (1) Families assigned to the placebo group may institute other environmental changes that have a greater impact than the studied intervention, and (2) a single environmental intervention is not likely to achieve significant results. Environmental control beyond impermeable bedding should be considered for every patient with allergic disorders but emphasized for those with moderate-to-severe disease. The limited inclusion of children does not invalidate the results of these well-executed studies.

— Howard Bauchner, MD

Published in Journal Watch Pediatrics and Adolescent Medicine August 11, 2003

Citation(s):

Woodcock A et al. Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma. N Engl J Med 2003 Jul 17; 349:225-36.

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Terreehorst I et al. Evaluation of impermeable covers for bedding in patients with allergic rhinitis. N Engl J Med 2003 Jul 17; 349:237-46.

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Platts-Mills TAE. Allergen avoidance in the treatment of asthma and rhinitis. N Engl J Med 2003 Jul 17; 349:207-8.

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• Medline abstract (Free)