House dust mite control measures for asthma.

Abstract

The major allergen in house dust comes from mites. Chemical, physical and combined methods of reducing mite allergen levels are intended to reduce asthma symptoms in people who are sensitive to house dust mites. The objective of this review is to assess the effects of reducing exposure to house dust mite antigens in the homes of mite-sensitive asthmatics, assessing chemical and physical methods separately and together. We searched the Cochrane Airways Group trials register, checked reference lists of articles and hand-searched Respiration (1980 to 1996) and Clinical and Experimental Allergy (1980 to 1996). The Cochrane Library is searched every three months. Randomised trials of mite control measures vs placebo or no treatment in asthmatic people known to be sensitive to house dust mites. Two reviewers applied the trial inclusion criteria, assessed their quality and extracted the data independently. Study authors were contacted to clarify information. Twenty-nine trials (939 patients in the analyses) were included, with two trials awaiting assessment. Nine trials assessed chemical methods alone, 15 physical methods alone, and 5 a combination of chemical and physical methods. Overall, there was no statistically significant difference improvement of asthma (relative risk 1.04, 95% confidence interval 0.83 to 1.31), asthma symptom scores (standardised mean difference -0.07, 95% confidence interval -0.35 to 0.22), medication usage (standardised mean difference -0.14, 95% confidence interval -0.43 to 0.15), or peak flow in the morning (standardised mean difference 0.04, 95% confidence interval -0.13 to 0.21). For chemical methods used alone, there was a statistically significantly adverse effect on symptoms (P = 0.03), whereas for physical methods used alone as evaluated in parallel group trials, there was a statistically significant beneficial effect (P = 0.02). However, because of the large number of significance tests we performed, two significant results would be expected to occur by chance. Currently available evidence from controlled trials of chemical and physical approaches to reducing exposure to house dust mite antigens in the homes of mite-sensitive asthmatics does not provide a secure basis for advice and policy. Further trials - one of them very large - are currently in progress. The additional evidence from these studies will help to clarify whether or not the substantial efforts required to implement strategies intended to reduce mites can be expected to yield beneficial effects of a magnitude that people with mite sensitive asthma consider worthwhile.