Survey of fungal contamination in ordinary houses in Japan

Background: Because fungi in the indoor environment strongly affect not only damage to and the deterioration of building materials, but also affect human health, it is important to know the distribution of fungi within an indoor environment. Therefore, in the present study, we examined fungi in houses over a period of 1 year and attempted to produce an indoor fungal contamination map for Japanese houses. Methods: Fungi were collected at approximately 100 fixed points in 81 ordinary houses around the Kanto District using either the stamp or dressing tape methods between 1999 and 2000. A commercially available potato dextrose agar culture medium was used to incubate the fungi collected. After incubation, fungi were quantified and identified by routine methods and the fungal conditions in the indoor environment was evaluated. Results: The relationships between the fungal conditions in the indoor environment found around the Kanto District and parameters such as the season, area in the house and indoor environment were analyzed. According to the fungal flora found in the present study, the indoor environment in Japanese homes was classified into three areas: (i) relatively wet areas, such as the bathroom, lavatory and kitchen, where hygrophilic fungi and yeasts are often detected; (ii) relatively dry areas, such as the living room and Japanese-style rooms, where xerophilic fungi are often detected; and (iii) areas where wet and dry parts coexist, such as bedrooms and closets containing futons and clothes with moisture, where both hydrophilic and xerophilic fungi, as well as yeasts, are detected. In the presnt survey, seasonal changes in the fungi detected in the indoor environment were small. Conclusions: We confirmed the actual fungal conditions in the indoor environment and produced a fungal map.