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Impermeable Bed Cover Use Does Not Lead to Improved Symptoms for Patients with Asthma or Allergic Rhinitis

Bed covers that are impermeable to mite allergens reduce the level of exposure to dust-mite allergen, the results of two studies show.

Using bed covers as a single avoidance measure, however, does not offer a significant improvement in clinical symptoms of patients with asthma or allergic rhinitis.

Ashley Woodcock, MD, of the University of Manchester, United Kingdom, and colleagues analysed the efficacy of mite allergen impermeable bed covers versus non-impermeable covers in 1,122 adults with asthma.

The 560 patients randomised to use impermeable bed covers had a prevalence of sensitivity to dust-mite allergen of 65.4%, while this prevalence was 65.1% in the 562 participants using normal covers.

After 6 months of use the concentration of Dermatophagoides pteronyssinus 1 (Der p1) in mattress dust was significantly lower in the impermeable cover group (geometric mean of 0.58 mcg/g) versus control (geometric mean of 1.71 mcg/g). However by 12 months there was no significant difference between groups (1.05 mcg/g in the impermeable group and 1.64 mcg/g in control).

At 6 months, mean morning peak expiratory flow rates in both groups improved significantly over baseline -- from 410.7 to 419.1 L/minute in the impermeable cover group and from 417.8 to 427.4 L/minute in control. However, the researchers noted no significant differences between the groups in morning peak expiratory flow rates or in the use of beta-agonists, in the rates of exacerbations, or in symptom and quality-of-life scores.

At 12 months the groups showed no significant difference in the proportion ceasing to use inhaled corticosteroid therapy or in the mean reduction in steroid dose.

In the absence of other mite-control measures, impermeable bed covers are clinically ineffective for the routine management of adults with asthma. "No effect was seen," Dr. Woodcock and colleagues write, "even in the subgroup of patients with high levels of mite-specific IgE and high levels of exposure to mite allergens."

In a related study, Roy Gerth van Wijk, MD, PhD, of Erasmus Medical Center, Rotterdam, Netherlands, and colleagues analysed the effects of mite-proof bed covers on the symptoms and signs of allergic rhinitis in 279 mite-sensitive patients 8 to 50 years old.

The patients were randomised to use impermeable or non-impermeable covers for their mattress, pillow, and duvet or blanket. The researchers measured concentrations of Der p1 and of D. farinae (Der f1), at baseline and after 12 months, in the patients' mattresses and bedroom and living room floors.

Among the 232 participants who completed the study, the geometric mean concentration of Der p1 and Der f1 in the mattress samples was significantly lower from baseline in the impermeable group (from 49.64 to 38.74 mcg/g of dust) compared with the non-impermeable group (from 44.07 to 32.32 mcg/g of dust).

Dust mite reductions were evident in the bedroom floor dust of the group using the impermeable covers but not in the non-impermeable cover group.

The researchers noted a significant decrease in mean score on the rhinitis-specific visual-analogue scale in both study groups (P<0.001 for both groups). But they found no significant difference between groups on the rhinitis-specific visual-analogue, the nasal allergen-provocation, or in the daily symptom scores.

This trial, "demonstrated a lack of clinical effect of mite-proof covers for mattresses, pillows, and duvets on signs and symptoms of rhinitis," Dr. Gerth van Wijk and colleagues write, "despite a significant reduction (by a factor of 2.6) in the level of exposure to house-dust mites in the mattress."

Related Link: Evaluation of impermeable covers for bedding in patients with allergic rhinitis (N Engl J Med 2003;349:3:237-46).
N Engl J Med 2003;349:3:225-36. "Control of exposure to mite allergen and allergen-impermeable bed covers for adults with asthma"

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