House dust mite (HDM) is a common inhalant allergen which can precipitate atopic disease episodes including asthma and allergic rhinitis. However, the relationship between HDM and asthma in subtropical regions of Asia, which may be affected by differences in climate and environmental variables, has not been widely studied. To assess this relation in the subtropical region of central Taiwan, we collected HDM samples from the houses of eight asthmatic patients as well as four normal subjects over a 1-year period. HDMs were collected by vacuum from the following four areas: living room floor, sofa, the top surface of child's mattress and bedroom floor. The mite concentrations, site distribution, seasonal variation, individual species and correlation with asthmatic attacks were studied. The HDM concentration had a seasonal variation, with the highest concentrations noted from July to November with gradually decrease from December to June. Among the four areas of collection, the highest concentration of mites was found on the child's mattress (p < 0.05). Dermatophagoides pteronyssinus was the dominant species (77%) and Dermatophagoides farinae was the second (13%). Our data showed that: 1. The highest concentrations of HDM occurred during the period from July to November. 2. The child's mattress was the household region with the highest percentage of HDM and thus should be considered of great concern as a likely source of the exacerbation of asthma. 3. D. pteronyssinus was the dominant species.
