The cholera bacterium can live in the environment in brackish (combined saltwater and freshwater) rivers and coastal waters. Shellfish, when eaten raw, have been a source of cholera. A few people in the United States have contracted the disease after eating raw or undercooked shellfish from the Gulf of Mexico.
In an epidemic, the source of the contamination is usually the feces of an infected person. Cholera can spread rapidly in areas with inadequate treatment of sewage and drinking water.
Once Vibrio cholerae is ingested, the bacteria travel to the small intestine where they begin to multiply. Vibrio cholerae then begins producing its toxin, which is the main cause of watery diarrhea, a characteristic symptom of cholera. In order to develop cholera symptoms, however, a person would need to ingest a considerable amount of Vibrio cholerae.