House dust mite control measures for asthma

BACKGROUND:

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.

OBJECTIVES:

To assess the effects of reducing exposure to house dust mite antigens in the homes of people with mite-sensitive asthma.

SEARCH STRATEGY:

We searched PubMed and the Cochrane Airways Group Register (last search July 2011). No restrictions were placed on language of publication.

SELECTION CRITERIA:

We included randomised trials of mite control measures versus placebo or no treatment in people with asthma known to be sensitive to house dust mites.

DATA COLLECTION AND ANALYSIS:

Two authors applied the trial inclusion criteria and evaluated the data. We contacted trial authors to clarify information.

MAIN RESULTS:

We included 55 trials (3121 patients). Thirty-seven trials assessed physical methods, including 26 trials employing mattress encasings. Ten trials involved chemical methods and eight trials involved a combination of chemical and physical methods. Despite the fact that many trials were of poor quality and would be expected to exaggerate the reported effect, we did not find an effect of the interventions. For the most frequently reported outcome, peak flow in the morning (1665 patients), the standardised mean difference (SMD) was 0.01 (95% confidence interval (CI) -0.08 to 0.11). There were no statistically significant differences either in number of patients improved (risk ratio 1.01, 95% CI 0.80 to 1.27), asthma symptom scores (SMD -0.06, 95% CI -0.16 to 0.05), or in medication usage (SMD -0.05, 95% CI -0.17 to 0.07).

AUTHORS' CONCLUSIONS:

Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended. It is doubtful whether further studies, similar to the ones in our review, are worthwhile. If other types of studies are considered, they should be methodologically rigorous and use other methods than those used so far, with careful monitoring of mite exposure and relevant clinical outcomes.