Affiliation: | Research Institute, International Medical Center of Japan, 1-21-1, Toyama, Shinjuku-ku, Tokyo 162, Japan;National Institute of Cholera and Enteric Disease, P-33, CIT Scheme XM, Beliaghata, Calcutta 700 010, India;National Institute of Infectious Diseases, 1-23-1, Toyama, Shinjuku-ku, Tokyo 162, Japan |