Allergen avoidance in the treatment of asthma: problems with the meta-analyses

Decreasing exposure to indoor allergens has been studied extensively and is a well accepted part of the treatment for allergic disease. The 2007 revision of the evidence-based guidelines recommends allergen avoidance as part of the management of asthma. In contrast, a recent meta-analysis concluded that dust mite avoidance is "of no use" in the treatment of asthma. There are obvious sources of bias that could have influenced the evaluation of published trials either by the guideline panel or by the group conducting the meta-analysis. An important issue is whether meta-analysis is a valid method of evaluating studies such as those on dust mite avoidance that are highly variable. Reading the published series of 4 meta-analyses on this subject from the Cochrane Library suggests that decisions about which trials to include can have a major effect on the outcome. The process of meta-analysis may also have other potential conflicts. The recent meta-analysis on dust mite avoidance appears to be seriously flawed because of the decisions about inclusion and exclusion as well as the way in which studies were evaluated. The conclusion is that the criticisms of the recommendations in the 2007 guidelines were not well founded.