Epidemiologic study of Vibrio cholerae O1 and O139 in Thailand: at the advancing edge of the eighth pandemic.

Vibrio cholera 0139 Bengal emerged on the Indian subcontinent in late 1992 and was first recognized in Thailand in 1993. To characterize the epidemiology of this disease, a hospital-based case-control study was conducted in Samutsakorn, a port city 30 km southwest of Bangkok. Between November 15, 1993, and June 3, 1994, cultures confirmed that 366 patients had cholera, including 165 (45%) with O139 Bengal, 191 (52%) with O1 Ogawa, and 10 (3%) with both serogroups. During the same time period in the previous year, 319 culture-confirmed cholera cases occurred, all serogroup O1. Questionnaires were completed for 217 (59%) of the 366 patients. 105 patients were infected with 0139 Bengal, 103 with V. cholera O1, and 9 with both serogroups. For each case patient, two asymptomatic age- and sex-matched control persons were selected. Of the 105 case patients with 0139 Bengal infections, 98 (93%) were adults (age 15 or older) compared with 95 (92%) of 103 patients with 01 infections. Patient infected with 0139 Bengal were more often male than patients with O1 (58% vs. 42%, p = .018). Cholera cases and matched controls were similar with regard to matching criteria of age and sex. Risk factors for cholera identified by case-control comparisons were similar for the two serogroups and included consumption of untreated water, uncooked seafood, and food served at group gatherings. Raw seafood exhibited a strong trend toward an association with O1 infections, and this variable was a significant risk factor among all cholera cases (matched odds ratio = 2.54). V. cholera 0139 Bengal rapidly displaced existing strains of V. cholera O1 and accounted for over 95% of V. cholera isolates in India and Bangladesh during the first year of its appearance. It has emerged in Thailand as a cause of endemic cholera with epidemiologic features and incidence similar to those of the preexisting O1 strain.