The strain of cholera that caused the recent outbreak in Haiti was introduced from a distant geographic source, probably South Asia, an expert study published by the New England Journal of Medicine (NEJM) has concluded.

Genome analysis shows that the type of cholera found in Haiti is "nearly identical" to a strain isolated in Bangladesh in 2002 and "predominant in South Asia", the report says. But the strain is distinct from types of cholera "circulating Latin American and East African strains of V. cholerae."

The Haitian cholera outbreak began in mid-October 2010 and has killed 3,333 people according to official figures. Many thousands more were sickened and required hospital treatment. The outbreak was a severe setback to reconstruction work following the January 12, 2010 earthquake that devastated the Haitian capital Port au Prince, killing 230,000 people.

Popular opinion in Haiti blamed the cholera outbreak on sewage spills into the Arbonite river from camps housing United Nations peacekeeping troops. The controversy exacerbated the already strained relationship between local people and UN peacekeepers.

In November a series of demonstrations demanded the withdrawal of a Nepali contingent of peacekeepers. Several people were killed during the disturbances, and demonstrators accused UN troops of firing into crowds. The BBC reported that at least one protester was shot dead by UN peacekeepers in Haiti's second city, Cap Haitien on November 16. A local official said the young man was shot in the back. The UN claimed he had been carrying a weapon.

The United Nations has repeatedly denied that its troops were responsible for the cholera outbreak, but in mid-December UN Secretary General Ban Ki-moon announced he was setting up an independent panel to investigate the epidemic.

"There remain fair questions and legitimate concerns that demand the best answer that science can provide," he said.

The outbreak of the Haitian Cholera Outbreak Strain by Chen-Shan Chin et. al. was published by the New England Journal of Medicine on January 6,, 2010.