House‐dust mites and associated environmental conditions in Danish homes

The Concentration of house‐dust mites (Dermatophagoides pteronyssinus) was investigated in 96 Danish homes with one or more members suffering from asthma. The air‐exchange rates, humidity, and temperature were measured in all the homes. A positive correlation was found between indoor air humidity and mite concentration (P<0.01), and an inverse correlation (P=0.027) between house‐dust mite concentration and indoor air‐exchange was found. Homes of mite‐allergic persons had a higher concentration of house‐dust mites than did those of the non‐mite‐allergic group. House‐dust mite concentration was above the proposed limit of 10 mites/0.1 g dust in 76% of the homes of persons allergic to mites and in 48% of the homes of nonsensitive persons. The high proportion of homes infested with house‐dust mites suggests an increased prevalence of house‐dust mites in Danish homes. The results support the concept that reduced ventilation in homes involves a risk of increased house‐dust mite exposure.