Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma.
BACKGROUND
The effectiveness of avoidance of house-dust-mite allergen (Dermatophagoides pteronyssinus 1 [Der p1]) in the management of asthma is uncertain.


METHODS
We conducted a double-blind, randomized, placebo-controlled study of allergen-impermeable bed covers involving 1122 adults with asthma. The primary outcomes were the mean morning peak expiratory flow rate over a four-week period during the run-in phase and at six months and the proportion of patients who discontinued inhaled corticosteroid therapy as part of a phased-reduction program during months 7 through 12. Der p1 was measured in mattress dust in a 10 percent random subsample of homes at entry and at 6 and 12 months.


RESULTS
The prevalence of sensitivity to dust-mite allergen was 65.4 percent in the group supplied with allergen-impermeable bed covers (active-intervention group) and 65.1 percent in the control group supplied with non-impermeable bed covers. The concentration of Der p1 in mattress dust was significantly lower in the active-intervention group at 6 months (geometric mean, 0.58 microg per gram vs. 1.71 microg per gram in the control group; P=0.01) but not at 12 months (1.05 microg per gram vs. 1.64 microg per gram; P=0.74). The mean morning peak expiratory flow rate improved significantly in both groups (from 410.7 to 419.1 liters per minute in the active-intervention group, P<0.001 for the change; and from 417.8 to 427.4 liters per minute in the control group, P<0.001 for the change). After adjustment for base-line differences (by analysis of covariance), there was no significant difference between the groups in the peak expiratory flow rate at six months (difference in means, active-intervention group vs. control group, -1.6 liters per minute [95 percent confidence interval, -5.9 to 2.7] among all patients [P=0.46] and -1.5 liters per minute [95 percent confidence interval, -6.9 to 3.9] among mite-sensitive patients [P=0.59]). There was no significant difference between the groups in the proportion in whom complete cessation of inhaled corticosteroid therapy was achieved (17.4 percent in the active-intervention group and 17.1 percent in the control group) or in the mean reduction in steroid dose, either among all patients or among mite-sensitive patients.


CONCLUSIONS
Allergen-impermeable covers, as a single intervention for the avoidance of exposure to dust-mite allergen, seem clinically ineffective in adults with asthma.
Woodcock
Ashley
A
South Manchester Academic Group, University of Manchester, North West Lung Centre, Wythenshawe Hospital, Manchester, United Kingdom. ashley.a.woodcock@man.ac.uk
Forster
Louise
L
Matthews
Edward
E
Martin
Jeannett
J
Letley
Louise
L
Vickers
Madge
M
Britton
John
J
Strachan
David
D
Howarth
Peter
P
Altmann
Daniel
D
Frost
Christopher
C
Custovic
Adnan
A
D000305:Adrenal Cortex Hormones / Q000008:administration & dosage; D000328:Adult; D000485:Allergens; D000818:Animals; D001249:Asthma / Q000188:drug therapy / Q000503:physiopathology / Q000517:prevention & control*; D001512:Bedding and Linens; D004311:Double-Blind Method; D004780:Environment, Controlled; D004781:Environmental Exposure / Q000517:prevention & control*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate; D039981:Pyroglyphidae / Q000276:immunology*
D000305:Adrenal Cortex Hormones; D000485:Allergens