The 2010 Haiti cholera outbreak, which sickened almost 300 000 people and claimed more than 4500 lives, was caused by bacteria inadvertently introduced into the country as a result of human activity, according to 2 independent studies.
In one study, French researchers and members of Haiti's Health Ministry provided circumstantial evidence that fecal contamination of a local stream that drained into the Artibonite River initiated the epidemic. The source of the contamination was a United Nations (UN) military camp with deficient sanitation that Nepalese soldiers were inhabiting, the researchers reported (http://tinyurl.com/3qudf6p). In the second study, an expert group working on behalf of the UN said that numerous factors contributed to the outbreak (http://tinyurl.com/3mhn8uf). They found that the Meye Tributary System of the Artibonite River was contaminated with a South Asian strain of Vibrio cholerae, but that the pathogen could not have spread without deficiencies in Haiti's water, sanitation, and health systems.
Friedrich MJ. Haiti Cholera Outbreak. JAMA. 2011;305(23):2402. doi:10.1001/jama.2011.831