[The epidemiology of allergy to house dust mites]

Currently, several studies show that sensitivity to mites is frequently found in the general population and in people suffering from respiratory allergic disorders. Thus 5 - 30% of the general population has positive skin tests whilst such sensitivity is found in 45 - 85% of asthmatic subjects. Certain studies have tried to establish a threshold of allergenicity beyond which the respiratory manifestations in allergic subjects became important. It seems after different studies that a threshold of 10 micrograms of antigen group I (the sum of the major antigens greater than Der p 1 and Der f 1) per gram of house dust may be a threshold beyond which the risk for the appearance of respiratory manifestation and in particular those of asthma in allergic subjects may be important. Moreover other studies tried to achieve a better understanding of the role of environmental conditions which favour the development of the mites. No or very few mites can develop if the relative internal humidity is less than 45% for an indoor temperature of 22 degrees C. These levels may be obtained in particular at altitude or in regions where the absolute outdoor humidity is low or the indoors are well heated and well ventilated. Epidemiological studies carried out in the last few years show that the relation between allergic respiratory mites disorders again show the frequency of diseases linked to the mites and the major influence of the environment as well as the idea of a tolerable allergenic threshold.