The relationship between carpeting period and the appearance of house dust mites(HDM)was investigated in 5 houses in the suburbs of Tokyo. The floors of the investigated rooms were entirely covered with new tile carpets, size 50 by 50 cm. Some of the carpets were removed at 1, 3, 6 and 12 months to examine the HDM and they were replaced by new tile calpets. Although the weight of fine dust from the 1-month carpets varied in each house, the mean weight of fine dust from the 1, 3 and 6-month carpets tended to increase with the carpeting period. The mean numbers of HDM also increased with the carpeting period. A total of 337, 616, 832 and 2, 635 mites/m
2 was observed for the 1, 3, 6 and 12-month carpets, respectively. Dermatophagoides farinae(Df)or D. pteronyssinus(Dp)dominated most carpets. The dominant rates of Pyroglyphid mites including Df, Dp and unidentified Dermatophagoides ranged from 35.7to100%, while those of the other species were 42.9% or less. It was considered that the HDM fauna dominated by Pyroglyphid mites stabilized after 1-month carpeting and dominating competition between these 2species of Pyroglyphid mites was not related to the carpeting period.
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