V. cholerae occurs naturally in the plankton of fresh, brackish, and salt water, attached primarily to copepods in the zooplankton. Coastal cholera outbreaks typically follow zooplankton blooms. Cholera is transmitted through ingestion of feces contaminated with the bacterium. The contamination usually occurs when untreated sewage is released into waterways or into groundwater, affecting the water supply, any foods washed in the water, and shellfish living in the affected waterway; it is rarely spread directly from person to person.

The resulting diarrhea allows bacteria to spread to other people under unsanitary conditions.