Cholera is an infection of the small intestine, caused by the bacterium Vibrio cholerae; the main symptoms are profuse, watery diarrhea and vomiting. The disease is transmitted primarily by drinking water or eating food that has been contaminated by the waste of an infected person, including one with no apparent or visible symptoms. The severity of the symptoms can lead to rapid dehydration, electrolyte imbalance, and–in some cases–death. The primary treatment is oral rehydration therapy–the ingestion of salt and sugar solutions via the mouth–or the admission of intravenous fluids if oral rehydration is too slow or not tolerated by the patient. Worldwide, cholera affected 3 to 5 million people and results in 100,000 to 130,000 deaths yearly. Notably, cholera was one of the earliest infections to be studied by epidemiological methods.