Within the year it spread to 11 countries, and subsequently throughout the continent. Until 1992, only V. cholerae serogroup O1 caused epidemic cholera. Some other serogroups could cause sporadic cases of diarrhoea, but not epidemic cholera. Isolation of this vibrio has now been reported from 10 countries in South Asia. It is still unclear whether V. cholerae O139 will extend to other regions, and careful epidemiological monitoring of the situation is being maintained.
Cholera is spread by contaminated water and food.
Sudden large outbreaks are usually caused by a contaminated water supply. In highly endemic areas it is mainly a disease of young children, although breastfeeding infants are rarely affected. Marine shellfish and plankton are the main reservoirs of V. cholerae. The El Tor strain can also survive in fresh water for long periods. Persons with asymptomatic infections play an important role in carrying V. cholerae from place to place, causing epidemics to spread.