House-dust mites and asthma. A review on house-dust mites as a domestic risk factor for mite asthma

Increased exposure to house-dust mites entails a greatly increased frequenc y of sensitization and increased frequency of mite asthma in the population . The available case-control studies demonstrate large variations worldwide in sensitization and disease risk dependent on the actual level of populat ion exposure. In areas with comparatively low population exposure to house- dust mites, there is a strong association between exposure and effect, whil e other areas with a more or less uniformly high population exposure do not demonstrate significant differences between patients and controls because the unexposed groups are too small. As to the existence of a hygienic maxim um threshold exposure level, current data all point to a single value of 10 0 mites/g of dust, corresponding to 2 mu g allergen/g of dust. This applies to the risk of sensitization and risk of disease, and when programs of pre vention imply exposure below this value, convincing clinical improvement is always observed. Today, the magnitude of the health problem related to pop ulation exposure to house-dust mites in many areas is comparable to the eff ects of active tobacco smoking and traffic accidents.