Effects of temperature and relative humidity on the prevalence pattern of the house dust mites, Dermatophagoides farinae and D. pteronyssinus

The prevalence patterns of the house dust mites, Dermatophagoides farinae (Df) and D. pteronyssinus (Dp), in relation to temperature and relative humidity in the room were investigated at 9 residences located in Tokyo, Kanagawa and Toyama Prefectures. Mite prevalence peaked in the summer season between July and September in most rooms sampled, although a peak appeared in the winter season between December and February in a few rooms. The prevalence could be classified into 3 patterns of Df, Dp and intermediate pattern according to statistical significance in the dominancy of the numbers. When 2 or more rooms were investigated in 1 residence, there was a similarity of the pattern among them. The largest numbers of mites were observed at 60-70% RH in Df and 80-90% RH in Dp, and rising mean temperature resulted in the mite increasing in that month. According to the results analyzed by Spearman's rank correlation test, suitable temperature and relative humidity in the room were considered to be 22.5-32.5℃ and more than 45% RH for Df, and 17.5-32.5℃ and more than 75% RH for Dp, respectively, i. e. Df preferred relatively lower humidity while Dp preferred higher. These results suggest that rising temperature promotes an increase in the number of mites, while relative humidity affects the proportion of both species of mites.