**Acknowledgements**

The authors appreciate the assistance of former colleagues from the Department of Hygiene, Kawasaki Medical School, Kurashiki, Japan, Professor Ayako Ueki, Drs. Yasuhiko Kawakami, Fuminori Hyodoh, Akiko Takata-Tomokuni, Yoshie Miura, Shuko Murakami, Ping Wu, Ying Chen and Megumi Maeda. The authors are also grateful for technical support from Ms. Yumika Isozaki, Haruko Sakaguchi, Tamayo Hatayama, Shoko Yamamoto and Miho Ikeda.
