Cholera is an infection of the small intestine caused by the bacterium Vibrio cholerae. The main symptoms are profuse, watery diarrhea and vomiting. Transmission occurs primarily by drinking water or eating food that has been contaminated by the feces of an infected person (even an asymptomatic one). The severity of the diarrhea and vomiting can lead to rapid dehydration and electrolyte imbalance, and death in some cases. The primary treatment is with oral rehydration solution (ORS) to replace water and electrolytes; if this is not tolerated or does not provide quick enough treatment, intravenous fluids can also be used. Antibiotics are beneficial in those with severe disease to shorten its duration and severity. Worldwide, it affects 3–5 million people and causes 100,000–130,000 deaths a year as of 2010[update]. Cholera was one of the earliest infections to be studied by epidemiological methods.