The various species of mites in the bedding dust and in a number of quilts of twenty patients in Hong Kong with house-dust allergy have been identified and counted and skin tests performed with extracts of Dematophagoides spp. and six storage-mites. These results are compared with a similar study in London. The particular environmental conditions which influence the numbers of mites and exposure to them have also been studied.
D. pteronyssinus is the most frequently occurring species in bedding dust in Hong Kong, as it is in London, and is found in higher numbers in the dust from quilts which appear to be the main source of allergy, as are pillows, blankets, eiderdowns and surface dust of mattresses in the U.K. All the patients of both groups gave positive skin-tests to this species.
Temperature, humidity and rainfall are all at their highest during the summer in Hong Kong, the time when quilts are discarded and stored, usually several together, in cupboards or drawers providing optimal conditions for breeding of mites and spread of infestation.
In a second group of eleven patients serial monthly D. pteronyssinus specific IgE-values, estimated by RAST, showed a peak in January approximately 2 months after increased exposure to the mites resulting from the quilts being put back onto the beds in October-November and an increase in the severity of patients' symptoms in November. There was a smaller peak in July possibly related to conditions caused by the high rainfall and cyclones in the preceding months.
Storage mites were found in higher numbers in Hong Kong than in London house-dust probably because sleeping rooms were often used for eating and cooking. The predominant species was Blomia tropicalis which produced the highest number of positive skin tests of the six storage-species. These species have little allergenic relationship with Dermatophagoides so that hyposensitization with the latter may not be effective in patients with associated, predominantly storage-mite allergy.