A person may get cholera by drinking water or eating food contaminated with Vibrio cholerae. In an epidemic, the source of contamination is usually the feces of an infected person. Cholera can spread rapidly in areas with inadequate treatment of sewage and drinking water.
Vibrio cholerae may also live in the environment in brackish rivers and coastal waters. Shellfish, when eaten raw, have been a source of contamination, and a few people in the United States have contracted cholera after eating raw or undercooked shellfish from the Gulf of Mexico.
Vibrio cholerae is not likely to spread directly from one person to another; therefore, casual contact with an infected person is not a risk for becoming ill.
Once Vibrio cholerae is ingested, the bacteria travel to the small intestine, where they begin to multiply. The bacteria then begins producing its toxin, which is the main cause of watery diarrhea, a characteristic symptom of cholera.
A person needs to ingest a lot of Vibrio cholerae in order to develop symptoms of cholera. The amount needed is decreased in those taking antacids, or following a meal, when the acids in the stomach are neutralized.