Seroepidetniologic studies during a simultaneous epidemic of infection with El Tor ogawa and classical inaba vibrio cholerae

A total of 247 family contacts of patients with El Tor Ogawa Vibrio cholerae and 73 family contacts of patients with classical Inaba V. cholera were studied during a simultaneous epidemic of both biotypes in Chittagong, East Pakistan, in 1968-1969. There was a distinctly different pattern of infection in family contacts. The infectiontocase ratio in El Tor Ogawa contacts was 36: 1, compared with 4: 1 for the classical Inaba family contacts. Even though the overall infection rates among family contacts were the same for both biotypes (46%), those contacts infected with El Tor Ogawa had a frequency of secondary hospitalized cases that was 8 times lower. The extrapolation of the hospital case rate to the incidence and prevalence of cholera infection in the community must take into consideration both the biotype and serotype of the infecting vibrio. Bacteriologic or serologic methods alone were not adequate to detect infections of either biotype. Combined usage of these techniques is recommended.