Department of Hygiene and Public Health, Nippon Medical School, Bunkyo-Ku, Tokyo, Japan

Correspondence to Tomoyuki Kawada, MD, PhD, Department of Hygiene and Public Health, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-Ku, Tokyo 113-8602, Japan. Tel: +81 3 3822 2131; fax: +81 3 5685 3065; e-mail: [email protected]