Mite asthma and residency. A case-control study on the impact of exposure to house-dust mites in dwellings.

The occurrence of mites in house dust from the homes of 25 patients with newly diagnosed house-dust mite asthma was much greater than that in the house dust from homes of 75 randomly selected matched control subjects. The difference in exposure corresponded to a relative risk of about 7.0, and a clear dose-response relationship could be demonstrated. The 25 patients lived in older and more humid houses than the control subjects did, which explains the greater number of house-dust mites found and suggests possibilities for and the necessity of introducing hygienic standards for the indoor environment as a measure of primary prevention in house-dust mite allergy.