Mite-proof covers may reduce severity of asthma exacerbations in allergic children

Bedcovers that form a barrier to house dust mites appear to reduce asthma flare-ups in children, according to new research published online, ahead of print in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.

In "Preventing Severe Asthma Exacerbations in Children: A Randomized Trial of Mite Impermeable Bedcovers," researchers in England report on a study of 284 children with asthma who tested positive for mite allergy, one of the most common asthma triggers. The children, ages 3-17, enrolled in the study after suffering an asthma flare-up, or exacerbation, that required being treated in the emergency room or as an inpatient at one of 14 hospitals in North-West England. After encasing their mattresses, duvets and pillows with mite-proof covers or placebo covers, the children were followed for a year. Neither the children, nor the investigators nor their health care professionals knew which set of covers the children received.

"Asthma exacerbations are among the most common reasons for hospitalizing children living in the developed world," said lead study author Clare S. Murray, MD, clinical senior lecturer at the University of Manchester and the Royal Manchester Children's Hospital. "It's a frightening experience for children and their parents, and a single exacerbation can increase the annual cost of treating asthma by three-fold."

Dr. Murray added that viral infections, especially those causing the common cold, are a major risk factor for asthma exacerbations in children sensitized and exposed to allergens. "Other studies have shown that these two risk factors act synergistically to increase the likelihood of hospital admission by nearly 20-fold," Dr. Murray said. "We have no means of protecting people from cold viruses, but our study indicates that allergen avoidance may be a cost-effective intervention."

The researchers found that children sleeping with the mite-proof covers compared to the placebo arm of the trial:
•Were less likely to have a severe asthma exacerbation that resulted in an emergency room visit or hospital admission (29.3 percent vs. 41.5 percent).
•Had a 45 percent reduced risk of having an asthma exacerbation that resulted in an emergency room visit or hospitalization and the requirement for systemic corticosteroids.
•Saw a significantly longer time between using the mite-proof covers and having their first exacerbation that resulted in an emergency room visit or hospitalization with the need for systemic corticosteroids.

The mite-proof covers did not significantly reduce the number of children whose exacerbation was treated outside the hospital with only an oral corticosteroid. The authors said it was not clear why this was the case. "It may be that the bedcovers did not prevent the exacerbation, but did reduce its severity," Dr. Murray explained.
Limitations of the study, which is believed to be the first to study the effect of mite-proof bedcovers and asthma exacerbations, include the fact that the exacerbations and oral corticosteroid use were reported by parents or guardians, not physicians, and the researchers had no information about viruses or other exacerbation triggers.

Although the study was not large enough to conclusively define the subgroups that benefitted the most from the intervention, the authors wrote that their results suggested that younger children testing positive for only house dust mite allergy and living in non-smoking households were more likely to benefit from the mite impermeable bed covers.

The authors estimated the cost of the bedcovers in the U.S. would be about $200. "This simple measure may reduce asthmatic exacerbations that lead to ER visits or hospitalization, particularly in younger children who are allergic only to dust mites," Dr. Murray said