▴ Woodcock A, Forster L, Mattehews E, et al. Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma. N Engl J Med2003;349:3OpenUrlCrossRefPubMedWeb of Science

This double blind, randomised study compared allergen impermeable bed covers with placebo covers in 1122 adults with asthma taking regular inhaled corticosteroids. The primary outcomes were mean morning peak expiratory flow rate (PEFR) at 6 months and the proportion of patients who discontinued corticosteroid treatment as part of a phased reduction programme during months 7–12. The mean morning PEFR improved significantly in both groups (from 410.7 to 419.1 l/min in the active intervention group, p<0.001; and from 417.8 to 427.4 l/min in the control group, p<0.001). After adjustment for baseline differences (by analysis of covariance), there was no significant difference in the mean morning PEFR between the groups. Analysis of the proportion of patients in whom complete cessation of inhaled corticosteroids was achieved showed no significant difference between the groups (17.4% in the active intervention group and 17.1% in the control group).

This study shows that allergen impermeable covers, as a single intervention for the avoidance of dust mite allergen, appear to be clinically ineffective in adults with asthma.