Study rumples claims that bedcovers ease allergy: dust mite controversy

Skin & Allergy News, Sept, 2003 by Betsy Bates

Adult patients with asthma and allergic rhinitis who encased their mattresses, pillows, and quilts in covers impermeable to dust mite allergen had no greater improvement in symptoms at 1 year than did patients with standard, cotton/polyester bedcovers, two large randomized, double-blind European studies revealed (N. Engl. J. Med. 349[3]:225-46, 2003).

The well-controlled studies conducted in Manchester, England, and Rotterdam, the Netherlands, stunned many American allergists and raised doubts about the widely held belief that special bedcovers represent one of the most highly effective allergy-control measures physicians can recommend for their patients.

Dr. Ashley Woodcock, primary investigator for the British study, said asthmatic adults in the United Kingdom have spent at least $100 million on an untested treatment, in addition to untold millions on special vacuum cleaners also shown by his group to be "an expensive waste of time."

In this country, efforts have been underway to seek third-party reimbursement for the covers at an estimated cost of $42 million a year.

"Doctors, I think, are culpable," recommending products marketed "purely on a nasty picture of a dust mite ... without the same level of evidence that you would need for a new drug, for example.

"I have been recommending them, so I am as guilty as anyone," Dr. Woodcock told this newspaper.

Dr. Peyton Eggleston, professor of pediatrics at Johns Hopkins University, Baltimore, expressed surprise at the study results.

"I imagine they were surprised, too. But that's why you do the study," he said in an interview.

More research is needed to determine whether a rigorous, comprehensive approach to indoor allergen control would reduce symptoms in adults, or whether mattress covers alone might help in pediatric cases, Dr. Eggleston said.

But until more information is available, he noted he would drop his support for third-party payer reimbursement for impermeable covers.

Dr. Dennis Ownby, chief of pediatric allergy and immunology at the Medical College of Georgia, Augusta, said he believes a similar study would produce similar results in children, despite an "almost religious belief" by some practitioners that dust mite precautions should reduce symptoms in mite-sensitive patients.

"The critical issue is whether it is possible in a home environment to reduce mite allergen levels to a low enough level to improve symptoms. It may be possible but it would make bedrooms look like hospital rooms and this may not be acceptable to individuals," he said in an interview.

The British study involved 1,122 adults with asthma who received home visits from a research nurse who fitted their beds with covers impermeable to dust mites or standard polyester-cotton blend covers. No special instructions were given about washing the covers or other bed clothing, nor about other standard allergen avoidance measures.

Pet owners and smokers were included in the study directed by Dr. Woodcock of the University of Manchester (England).

Sixty-five percent of enrollees proved to be dust mite-sensitive, although this information was not available to investigators conducting the study.

"We deliberately decided not to conduct a study in a carefully selected minority of patients, with strict criteria for inclusion and exclusion and extensive intervention, since the results of such a study might not be widely applicable," the investigators said.

It was, they said, intended to be a "pragmatic clinical trial investigating the effect of a simple, practical intervention, which mimicked real-life clinical practice as much as possible."

The special mattress covers significantly reduced the concentration of dust mites in patients' mattress dust at 6 months, but not 12 months, into the study.

Morning peak expiratory flow rates improved for both groups after 6 months, but there were no significant differences between those who received protective mattress covers and those who did not, even when investigators looked specifically at mite-sensitive patients.

Use of [beta]-agonists, daily symptom scores, rates of exacerbations, and quality of life scores also were similar in both groups.

During the second 6-month phase of the study, about 17% of the patients who received impermeable mattress covers, and the group who did not were able to discontinue inhaled corticosteroid therapy.

The study concluded that "in the absence of other mite-control measures, [dust mite allergen-impermeable covers] ... are clinically ineffective for routine management of adult asthma in primary care."

The Dutch study enrolled 279 adults with allergic rhinitis who were similarly randomized to receive impermeable or nonimpermeable bed covers for 1 year.

In this study, patients were instructed to use the covers in conjunction with a program of allergy control that involved washing bedding weekly in hot water, cleaning their homes, and controlling heat and ventilation in their homes.

Although dust mite allergen levels were reduced significantly more in homes where impermeable bedding covers were employed, the intervention made no difference in patients' symptom in the study.