A randomized controlled trial of mite allergen-impermeable bed covers in adult mite-sensitized asthmatics

BACKGROUND: Mite-allergic patients with allergic disease should benefit from avoiding mite allergens. Many physicians, however, are yet to be convinced that allergen avoidance can make a significant contribution to asthma management in these patients. Many allergen-avoidance regimes include multiple measures of allergen reduction, but as mite exposure in the home is most likely to be greatest in bed dust, bedding is usually the first target for intervention. OBJECTIVE: This study selected adult patients considered to be most likely to benefit from avoiding mite allergens, namely diagnosed asthmatics, sensitized to house dust mites and exposed to mite allergen in their mattresses. Patients were randomized into a placebo-controlled trial of the use of allergen-impermeable bed covers for 12 months, without any other form of mite-reduction measures. METHODS: Adults with asthma were selected from general practices and asthma clinics in south-east London. Their serum IgE to mite allergens and allergen content of mattress dust samples were measured. Those with >0.70 kU/L mite-specific IgE and >2 microg/g Der p 1 were randomized into active or placebo treatments. Information was collected on allergic symptoms and medication use and quarterly peak flow diaries were kept throughout the trial. Dog or cat allergic patients were excluded if they had a pet at home to which they were sensitized. RESULTS: The mean decrease in microg/g Der p 1 was 25.7 (95% CI 8.9, 74.1) in the active group and 4.5 (95% CI 1.8, 11.5) in the placebo group. Der p 1 concentrations in the active and placebo groups at the end of the trial were not significantly different. There was no effect on peak flow or asthma symptoms in a simple comparison of the treatment and placebo groups. CONCLUSION: In this group of patients, mite allergen avoidance in the bed by the use of allergen-impermeable bedding alone cannot be recommended as an effective way of relieving asthma symptoms.