It would be more accurate to talk about the cholera outbreak as biology rather than chemistry. Cholera is an infectious disease that is caused by the bacteria Vibrio cholerae. It causes serious diarrhea and vomiting and if untreated can cause death. The bacteria that causes cholera is spread through fecal matter of an infected person contaminating food and water in a populated area. If a populated area experiences a sudden explosion of cholera cases, an outbreak is said to occur.
Haiti has experienced a serious cholera outbreak over the past three years. Although it has not been proven, the most likely cause of the initial outbreak was poor sanitation from a UN base housing representatives from Nepal. The poor sanitation at the base contaminated the Artibonite River, a source of drinking water in Haiti. Compounding the initial outbreak was the fact that a massively devastating earthquake occurred 10 months later, leaving large numbers of people without proper sanitation for an extended period of time. This made a bad situation worse by allowing the spread of the bacteria to flourish in Haiti.