Image: Dust mite
FDA.gov
Live dust mites aren't the real problem. Their waste and decaying bodies contain a protein that mixes with household dust and becomes airborne, triggering wheezing, sneezing, watery eyes and runny noses in mite-sensitive people.
By JoNel Aleccia Health writer
msnbc.com
updated 4/17/2008 4:34:32 PM ET 2008-04-17T20:34:32

For more than two years, Theresa Lansberry has fought a daily battle against household dust. 

Ever since doctors diagnosed her husband and, later, her oldest daughter, with allergic asthma triggered by dust mites, she has waged war against the millions of microscopic, spider-like creatures that inhabit the cozy corners of most homes.

She ripped out carpets and replaced them with wood. She banned certain stuffed animals and relegated others to a weekly hot-water wash with mite-killing soap. She spent time, energy and money on dozens of other interventions aimed at keeping life-threatening asthma attacks at bay.

“I’ve bought the steam cleaners and the mattress covers and I don’t use curtains in our bedroom,” says Lansberry, 33, a mother of six from Peoria, Ill.

Until now, Lansberry thought she was winning. But a new review of studies released this week suggests that she and others affected by asthma might as well give up the fight.

In 54 trials involving more than 3,000 patients, the most widely recommended treatments to reduce dust mites had no effect on the symptoms of asthma sufferers, researchers in Denmark found.

Dust mites are tiny organisms that thrive in the company of humans, feasting on dead skin cells and nesting in soft, dust-collecting places such as bedding, carpets and cloth-covered furniture.

“Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended,” wrote Dr. Peter Gotzsche, director of the Nordic Cochrane Center in Copenhagen.

That means patients tempted to try cures ranging from powders and sprays to air ionizers and expensive HEPA-filter vacuum cleaners shouldn’t bother, said the researchers, who have studied the issue in periodic reports for more than a decade.

"It is patients who pay for useless interventions, not doctors," Gotzsche said.

In addition, national and international allergy agencies should stop advocating treatments that don’t work, he said.

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“Reviews and guidelines should reflect the facts,” the report concluded.

Dust mites aren't the only culprit
That recommendation drew the ire of the Asthma and Allergy Foundation of America, whose members routinely advise the criticized techniques. The Denmark study is “myopic,” said Mike Tringale, the asthma advocacy agency’s director of external affairs.  It focused only on studies of dust mites, instead of the range of possible household allergens.

“There’s not one cause of the problem and there’s not one solution,” said Tringale.

He added that the review was incomplete and omitted studies that showed limiting dust mites improves asthma symptoms, a charge that Gotzsche denied.

Reducing dust mites has to be part of an overall plan that may include medication and other interventions, such as removing pets from the home or eliminating smoking, Tringale said.

The studies reviewed by the Denmark team ranged from trials of two weeks to two years. They included several techniques aimed at reducing dust mites.

Researchers used chemicals to poison the critters and physical interventions to get rid of them. They tried sheathing mattresses and pillows in mite-proof covers, washing bed linens frequently in very hot water and removing dust-harboring furniture, toys, plants and other items from homes.

Some of the studies did manage to reduce the amount of mites by 50 percent or more. But that still had no effect on the asthma patients’ symptoms, probably because it’s not possible to reduce the mites enough, Gotzsche indicated.

"The levels are so high that the reduction that can be obtained has no effect on the asthma," Gotzsche said.

In some people, even small amounts of the allergen can trigger attacks.

It’s not the mites themselves that cause problems. Their waste and decaying bodies contain a protein that mixes with household dust and becomes airborne, triggering wheezing, sneezing, watery eyes and runny noses in mite-sensitive people.

Of the 20 million people in the United States with asthma, between 12 million and 14 million suffer from allergic asthma. About half of those people are sensitive to dust mites, said Dr. Gailen D. Marshall, director of the Division of Clinical Immunology and Allergy at the University of Mississippi Medical Center.

Marshall said he doesn’t doubt the dust mite findings from the Cochrane Collaboration, which is widely respected for its evidence-based reviews.

“What this does for me in practice is that I can’t just say ‘Put a cover on your mattress and a filter in the corner and buy an expensive vacuum,’” he said. “It is just one component.”

However, Marshall added that few experts would recommend reducing dust mites as the sole approach to treating allergic asthma.

“If you have pets in the home, dust mite control isn’t going to help,” he said.

The Denmark review will help narrow the focus of allergic asthma treatments, predicted Noreen M. Clark, a professor of public health at the University of Michigan. The most important treatment is effective medication in the right dosage, she noted.

Asthma triggers vary widely
Beyond that, patients must remember that asthma triggers can vary widely according to the person and the environment.

“We always advise patients to become detectives, that is, to observe themselves and their situations to see what kicks off their symptoms,” she said.

The new study raises doubts for Theresa Lansberry, an editor for the online parent advice Website Type-A Mom. While she’s happy to take measures to help her husband, James, 38, a nonprofit agency manager, and their daughter, Moriah, 12, she’s not always sure it’s effective.

“Each time my husband has breathing problems, I’ll do the deep clean in the bedroom and he gets better,” she said. “Can I say it’s because of that? No.’”

Still, Lansberry said she’ll probably continue her dust-mite combat despite studies that show it’s a waste of time.

“It’s kind of creepy when you learn about dust mites. They’re everywhere,” she said. “I like the idea of doing something to get rid of them.”

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