Exposure to house dust mites in homes of people with atopic dermatitis

The median relative density of house dust mite populations was determined in mattresses in the homes of 23 people with atopic dermatitis (AD) who were mite-sensitive. It was significantly higher (total mites [dead and live] 174/0.1 g of dust: live mites 45.5/0.1 g) than in those of 23 healthy non-atopics (total mites 52/0.1 g; live mites 7.5/0.1 g; P < 0.05, < 0.01, respectively; Mann-Whitney U-test). There was no significant difference between mite population densities in mattresses in damp homes (n = 27; total mites 188/0.1 g; live mites 36/0.1 g) and those in homes with no damp (n = 19; total mites 116/0.1 g; live mites 26/0.1 g). These data demonstrate a clear association between AD and exposure to large numbers of mites, independent of the presence of domestic damp. People with AD were exposed to densities of > 500 mites/0.1 g of mattress dust five times more frequently than non-atopics, corresponding to a relative risk of 25.0, but were exposed to densities of < or = 50 mites/0.1 g five times less frequently. The overall relative risk for AD, with a cutoff of 50 mites (total)/0.1 g, was 8.1. There was an obvious positive correlation between magnitude of exposure and frequency of disease. It is hypothesized that the association between high densities of mites and AD is related to differences in lipid composition of the shed squames on which the mites feed: those of people with AD may be of greater nutritional value than those of non-atopics, thus enhancing mite population growth.