Mite-Proof Covers Alone Don't Help Asthma

Dust-mite-proof bed covering, often recommended by doctors to help asthma and allergy patients, aren't enough to stop sufferers from wheezing and sneezing, two new studies find.

The studies, published in today's New England Journal of Medicine, find that mite-proof bed coverings alone do not lead to a significant improvement of clinical symptoms in patients with asthma or allergy. However, experts emphasize that the coverings still may be useful as part of a more comprehensive treatment strategy.

As many as 50 million Americans have allergies, and many of them are sensitive to dust mites — near-microscopic creatures that live in house dust and lay their eggs in places such as bedding. To combat this, many doctors have recommended that their patients use specially woven mite-proof covers, which typically cost less than $100.

"The important message from these studies is that the use of mattress covers [and pillow covers] as an isolated strategy, when applied broadly to an unselected group of patients with asthma or allergic rhinitis, does not appear to bring about a measurable benefit," said Dr. Aidan Long, clinical director of allergy at Massachusetts General Hospital.

The studies, conducted in England and the Netherlands, found that after one year, there was no difference in symptoms between people who used these bed coverings and those who didn't. The English study looked at 1,122 asthma patients, and the Dutch study observed 232 with hayfever-like allergies.

So should patients stop using mite-proof covers? Not so fast.

Need for More Comprehensive Allergen Avoidance

While the covers alone seemed to provide little benefit, Long emphasized the studies should not be interpreted as meaning mite-proof covers are worthless. Indeed, patients with allergies to dust mites may find them helpful when used as part of a comprehensive mite allergen-avoidance program.

As many as 40 percent to 60 percent of allergy sufferers are sensitive to dust mites.

"It remains very likely that these products are very helpful when used in the appropriate patient and, when necessary, in conjunction with other strategies to modify environmental allergen exposure," Long said.

Other experts agreed.

"Reduction of exposure to dust mites has been shown to improve asthma and allergy control," said Dr. Carolyn M. Kercsmar, professor of pediatrics at Case Western Reserve University in Cleveland. "These studies mostly demonstrate that dust covers alone may not be enough to cause significant improvement in symptoms."

"I think the data in this study fits in very well with what we know," said Dr. William Calhoun, director of the Asthma, Allergy, and Airway Research Center at the University of Pittsburgh.

Calhoun said while mite-proof covers can reduce exposure to allergens, in order to see clinically significant results, evidence shows that exposure needs to be reduced by at least 90 percent to 99 percent — something that mite-proof coverings alone may not be able to provide. Both studies showed that using the covers only reduced mite exposure by about 65 percent.

"In short, the interventions taken were insufficient to make a biological difference," he said.

Few allergists would recommend bed covers alone as dust-mite mitigation anyway, said many experts. While complete reduction of allergen exposure may be an impossible task, allergists usually give their patients a combination of suggestions to reduce their exposure to allergens.

"I'm not going to throw in the towel, I'm still going to recommend it," said Dr. Clifford Bassett, an allergy expert at the New York University School of Medicine. "An ounce of prevention is a pound of cure. If you can do something to benefit your patients, you should. In no way do I think [the findings] are a negative."

Bassett and other allergists say they often give patients a combination of suggestions for treatment of their symptoms.

Washing bedclothes in hot water, eliminating carpeting in the bedroom, and changing bedding at least weekly are essential measures patients should take, experts say.

Other additional measures may include removal of cats, dogs or other furry animals from the patient's environment; reducing indoor humidity, exposure to cigarette smoke and other irritants; and watching out for sources of mold spores and cockroach allergens.

"What these studies tell us is that a 'one size fits all' approach to environmental modification is unlikely to be helpful," said Long. "Doctors should emphasize the importance of determining which allergens are relevant for a given patient and tailor their recommendations concerning allergen and irritant avoidance to each individual patient."

"Generally, it is still sensible for patients with asthma or allergies to be tested to learn what they are allergic to and to try to reduce or eliminate their exposure to those factors," said Dr. Gregory Diette, co-director of the Asthma Clinic at Johns Hopkins University in Baltimore.

Calhoun agrees. "Simply buying a mattress cover is not enough. The allergen-avoidance strategy should be comprehensive, and coordinated by an allergist."

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