Epidemiological patterns and incidence of bio-, sero- and phage types of Vibrio cholerae in Hyderabad, India, during 1971-1984.

During 1971-1984 out of 44,762 gastroenteritis cases bacteriologically examined, 4240 (9.5%) Vibrio cholerae were isolated in Hyderabad, India. Out of them 1329 (31.3%) were classical and 2911 (68.7%) were el-tor biotypes. The changeover from classical to el-tor cholera was observed in Hyderabad during 1975 and persisted. During this 14 year period four major outbreaks with V. cholerae serogroup O1 Ogawa, V. cholerae biotype el-tor serogroup O1 Ogawa were observed. Phage types 1, 2 and 4 were prevalent during the classical period and types 2 and 4 during the el-tor period. Of the cholera patients, 67% were under 30 years of age with no significant difference in the incidence among females (51.4%) and males (48.6%). The outbreaks were of protracted pattern with only few cases per day or week with peak incidence during monsoon (May-August). Community of the low socio-economic strata was the most susceptible group. Five zones situated at the outlet of the Moosi river in the downhill were recorded as extensive cholera transmission zones and two of them were the primary foci of infection. The severity of the infection was found directly related to the average rainfall during the year leading to the sewage stagnation in the downhill.