A cholera outbreak that has killed more than 300 people in Haiti matches strains commonly found in South Asia, the U.S. Centers for Disease Control and Prevention says.

The finding is a significant step toward answering one of the most important questions about the burgeoning epidemic: How did cholera, a disease never confirmed to have existed in Haiti, suddenly erupt in the vulnerable country's rural centre?

It also intensifies the scrutiny of a UN base that is home to recently arrived Nepalese peacekeepers, built on a tributary to the Artibonite River. Cholera has been detected in the waterway, and most of the cases have been among people who live downriver and drank from the Artibonite, says a CDC report released Monday.

Speculation among Haitians has increasingly focused on the base and the troops from Nepal, where cholera is endemic and which saw outbreaks this summer before the arrival of the current contingent of troops. On Friday, hundreds of protesters demanded the Nepalese peacekeepers be sent home.

In an unannounced visit to the base last week and a tour of the facility given by peacekeepers on Sunday, The Associated Press found questionable sanitation conditions.

The UN has defended its sanitation practices and denied that it was a source of the infection. A spokesman said the agency was looking into the matter Monday following the announcement.

CDC researchers identified the strain by analyzing DNA patterns that can be compared with those from other regions of the world, Dr. Christopher Braden told AP. The results were given to the press on Monday after being released to Haitian health authorities.

The finding does not identify the source of the disease or say how it arrived in Haiti, but it eliminates some other possibilities, including a suggestion that the strain might be related to a 1990s South American outbreak, Braden said. South Asia refers to the area around the Indian subcontinent — India, Pakistan and other countries including Nepal, he said.

"That's all we can say at this point, and we'll know more as more research is done," Braden added.