PORT-AU-PRINCE, Haiti (AP) — A cholera outbreak that has killed more than 300 people in Haiti matches strains commonly found in South Asia, the United States Centers for Disease Control and Prevention said Monday.

Researchers identified the strain by analyzing DNA patterns that can be compared with those from other regions of the world, according to Dr. Christopher Braden, a C.D.C. epidemiologist.

The finding does not identify the source, nor does it explain how cholera — a disease never confirmed to have existed in Haitisuddenly erupted in the vulnerable country’s rural center. But it eliminates some possibilities, including any connection to a 1990s South American outbreak.

The finding also intensifies the scrutiny of a United Nations base 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.

Speculation among Haitians has increasingly focused on the base and troops there from Nepal, where cholera is endemic and which saw outbreaks this summer before the current contingent of troops arrived in Haiti. Most people infected by the microbe never develop symptoms but can still pass on the disease.

On Friday, hundreds of demonstrators waving tree branches and carrying anti-United Nations banners walked from the central plateau city of Mirebalais several miles to the gates of the base. “Like it or not, they must go,” they chanted.

The United Nations has defended its sanitation practices and denied that the base could be a source of the infection. A spokesman said the agency was looking into the matter on Monday following the C.D.C.’s announcement.

In the coming weeks, additional laboratory testing, including whole genome DNA sequencing, will be conducted, but investigating officials note that such testing may never fully explain how cholera was introduced into Haiti.

“Our primary focus here is to save lives and control the spread of disease,” said Dr. Jordan Tappero, the epidemiologist who is leading the C.D.C.’s cholera response team in the country. “We realize that it’s also important to understand how infectious agents move to new countries. However, we may never know the actual origin of this cholera strain.”