Background: Estimated indoor climate conditions in unheated summer cottages offers house-dust mites unfavorable temperature and feeding conditions while giving them optimum humidity conditions. We aimed to estimate the exposure level of house-dust mites in summer cottages.
Methods: A total of 37 summer cottages were sampled for house dust and storage mites in three locations and the results compared with samples from 33 patients suspected of house-dust mite allergy and living in ordinary houses. The processed dust samples were investigated by microscopy and exposure levels given as number of mites per 0.1 g dust.
Results: The summer cottages were without exception all heavily infested with threefold or higher concentrations of both house dust and storage mites in comparison with ordinary houses. In unheated summer cottages were found tropical high concentrations of house dust and storage mites with a median concentration of house-dust mites in mattress dust of 2000 house-dust mites/g of dust which corresponds to an average of 40 μg allergen/g of mattress dust.
Conclusions: As a probable consequence of high indoor air humidity conditions in unheated summer cottages in winter, dust samples contained threefold or higher concentrations of house dust and storage mites. Indoor humidity conditions thus more than compensated for lack of continuous supply of skin scales from human beings and an unfavorable low indoor air temperature. The uniform high mite exposure in summer cottages is likely to imply disease deterioration in patients already allergic to mites.