A woman carries a child with symptoms of cholera at the entrance of a hospital in the Cite Soléil neighborhood of Port-au-Prince in November. (Ramon Espinosa/Associated Press)

The cholera strain behind Haiti's outbreak closely matches samples of bacteria from South Asia, and not those from Latin America, researchers have found.

Since cases of cholera were first confirmed in Haiti's Artibonite province on Oct. 19, the outbreak has killed more than 2,000 people. Many public health leaders believe the disease's spread has not yet peaked.

Human activity from a "distant" geographic source is likely how the epidemic began, researchers report in Thursday's online issue of the New England Journal of Medicine.

"Our data distinguish the Haitian strains from those circulating in Latin America and the U.S. Gulf Coast and thus do not support the hypothesis that the Haitian strain arose from the local aquatic environment," Matthew Waldor, a professor of medicine at Harvard Medical School, and his co-authors concluded.

"It is therefore unlikely that climatic events led to the Haitian epidemic, as has been suggested for other cholera epidemics."

The location and timing of the outbreak coincided with the arrival of UN peacekeepers from South Asia, leading to speculation that the disease may have been carried by troops from Nepal.

But the researchers caution that determining the source of the Haitian strain more precisely will require more investigation.

The new report is consistent with the Nepalese hypothesis, but Waldor noted the researchers didn't compare the Haitian samples with those from Nepal or test Nepalese troops stationed in Haiti.

New technology used

To identify the likely origin of the strain, the scientists used a new DNA-sequencing method and imaging technology to watch a natural enzyme synthesize a strand of DNA and track changes.

The analysis showed a relationship between Haitian samples and strains isolated in Bangladesh in 2002 and 2008.

"The Haitian epidemic is probably consequent to introduction, through human activity, of a V. cholerae strain from a distant geographic source," the study's authors wrote.

Haiti had been cholera-free for about 100 years, the researchers said.

The findings are similar to an earlier report by the U.S. Centers for Disease Control and Prevention that was based on older technology.

Based on the latest findings, Waldor and his co-authors suggested that a cholera vaccination campaign might not only control the disease but it could also minimize spread of the strong strain beyond the shores of Hispaniola, the island that Haiti shares with the Dominican Republic.

To minimize spread, Waldor suggested that troops or relief workers from a country where cholera is widespread should take preventive steps — such as routine screening for disease and giving antibiotics or a dose of vaccine — before they they are sent to disaster zones.

The research was funded by the U.S. National Institute of Allergy and Infectious Diseases.

With files from The Associated Press