Limitations of studies highlighted: don't throw away dust mite mattress covers yet.(Clinical Rounds)

SAN FRANCISCO -- Recent well-publicized studies have suggested that dust mite mattress covers are not effective for improving allergy and asthma.

But before physicians tell their patients to throw away their mattress covers, they may want to consider some of the limitations of these studies, Dr. Theodore M. Freeman said at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.

"I have been very uncomfortable with this conclusion" that mattress covers are not helpful, said Dr. Freeman, chairman of the allergy and immunology department at the U.S. Air Force's Wilford Hall Medical Center, San Antonio.

"I certainly haven't changed my practice. I still tell all my patients about dust mite covers and avoidance," Dr. Freeman said.

The studies were rigorously conducted, randomized trials, but they sought to assess the benefit of dust mite covers as a single intervention--and that is a problem, Dr. Freeman said. Many experts and researchers are convinced that patients need to institute a combination of measures to adequately reduce their exposure to dust mite allergen. These measures include washing bedding regularly at the proper temperature, cleaning floors, and perhaps even room air filters. It may not be possible to separate each measure out experimentally.

Two widely discussed articles on the topic appeared in the New England Journal of Medicine.

In one of those studies, 1,122 adults with asthma were given either an allergen-impermeable mattress cover or a nonimpermeable cover as a control. At 6 months, the groups of patients had roughly equivalent improvements in morning peak expiratory flow rate. At 12 months, both groups had similar reductions in mean corticosteroid usage and similar proportions had stopped using ...