Clinical effects of allergen avoidance

The costs of asthma care are increasing. A successful, simple and widely applicable environmental intervention could have major benefits. Although all trials of bed coverings suggest they are clinically effective, the impact of their widespread use by asthmatics has not been determined in a public health context. In 1992, the British Society of Allergy and Clinical Immunology Working Group reviewed all the published data and, agreed on the inadequancy of avoidance trials and the need for a large-scale study on mite-allergen avoidance (97). More recently, the Third International Workshop on Indoor Allergens and Asthma stated: “There is an urgent need to develop adequately-powered, randomised, controlled studies to investigate the potential benefits of low-allergen domestic environments in patients with allergic disease. Such studies need to address compliance, cost effectiveness, be of adequate length (e.g., 12 months), and be tailored for different socio-economic groups and age groups” (98). The 1997 revision of the British Thoracic Society Asthma Guidelines states: “Support for house dust mite avoidance measures reflects a change to the 1993 Guidelines, but further research into methodology and duration of action of these measures is needed” (99). There remains an urgent need to develop a large-scale trial of the widespread applicability of miteallergen avoidance and the effect on patient symptoms, exacerbation rate, use of medication, and overall health costs. One such study on the effect of mite-allergen avoidance by the use of allergen-impermeable bedding on asthma control in adults is currently being carried out in the United Kingdom (100). This is a randomized, parallel-group, double-blind, placebo-controlled trial, with 2000 patients entering the run-in period and 1800 being randomized. During the first 6 mo of the trial (phase A) patients will take their usual inhaled steroid therapy, and during the next 6 mo (Phase B, mo 6\2-12) patients will make a controlled reduction of inhaled steroids. The results of this study will show conclusively whether a simple intervention designed to reduce domestic mite-allergen exposure can improvethe clinical control of asthma, which subgroups of patients benefit, and whether a reduction in regular inhaled steroid use can be achieved in primary-care patients.