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 U.S. Centers for Disease Control and Prevention said Monday.

The finding intensifies scrutiny on a U.N. base above a tributary to the Artibonite River that is home to a contingent of recently arrived peacekeepers from Nepal, a South Asian country where cholera is endemic and which saw outbreaks this summer.

It is also 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 center?

Speculation among Haitians has increasingly focused on the U.N. base. The outbreak began among people who live downstream from where the tributary meets the Artibonite and drank from the river. On Friday, hundreds of protesters marched from the nearby city of Mirebalais to demand the Nepalese peacekeepers be sent home.

The Associated Press found questionable sanitation in an unannounced visit to the base last week and an exclusive tour of the facility given by peacekeepers Sunday. Despite earlier statements that sanitation at the base was up to international standards, on Monday the mission acknowledged there are santiation problems and said they are being solved.

Following the CDC report, U.N. mission spokesman Vincenzo Pugliese said U.N. personnel took environmental samples around the base Oct. 24, including from septic tanks, and tests by a private laboratory found no cholera.

He added that the mission “welcomes the scientific contribution of the national public health laboratory in Haiti and the CDC to the understanding of the current cholera outbreak in Haiti.”

CDC researchers identified the strain by analyzing DNA patterns that can be compared with those from other regions of the world using a method of “DNA fingerprinting” called pulsed field gel electrophoresis. The samples were taken from cholera patients, and the results were released to the press Monday after first being given to Haitian health authorities.

South Asia refers to the area around the Indian subcontinent — India, Pakistan and other countries including Nepal, Dr. Christopher Braden at the CDC said.

The finding does not identify the source of the disease or say how it arrived in Haiti, but it eliminates other possibilities including a hypothesis that the strain might be related to a 1990s South American outbreak, Braden said. He said the strain was “fairly common.”

Researchers said global travel and trade provide “many opportunities for infectious diseases such as cholera to spread.”

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

The outbreak is spreading across Haiti, its transmission eased by a lack of immunity among the population. A confirmed case of cholera had never been detected in Haiti before the current outbreak, said Claire-Lise Chaignat, head of the World Health Organization’s global task force on cholera control.

Cholera bacteria spread when people consume water or food contaminated with feces that contain the disease. Twelve days after it was first reported in Haiti, it had killed at least 337 people and hospitalized more than 4,700.

The epidemic has impeded aid workers’ ability to prepare for Tropical Storm Tomas, which is expected to strike Haiti later in the week as a hurricane. Aid workers are concerned that floods could spread the disease further.

Suspicions about the base were seized upon by politicians who oppose the 12,000-member U.N. mission, which has been the dominant security force in Haiti since it arrived after the 2004 ouster of President Jean-Bertrand Aristide. Among the politicians are the mayor of Mirebalais, who is running for Senate in the planned Nov. 28 election.

So far there has been little formal effort to find exactly where and how the bacteria entered Haiti’s water and food supply.

Pugliese said peacekeepers do not see a need for an independent investigation in an effort to avoid “accusatory finger-pointing … completely based on speculation that could really harm the reputation of our Nepalese here.”

“The soldiers are healthy. The test proved negative. The sanitary problem we had, we’re fixing it. I don’t see any need for an investigation into the base,” he said.

But, he added: “If the ministry of health or the CDC decides to conduct such an investigation we stand ready to cooperate and to give them full access to our base.”

The CDC has not sent a team to the area around the base or tested environmental samples.

The AP visited the Nepalese U.N. base last Wednesday to follow up on a statement by the mission that its sanitation measures met U.S. and U.N. standards. The area between the base and the river reeked of human waste. Several pipes were leaking, including a broken plastic pipe emitting a foul-smelling black liquid near what the soldiers identified as latrines. A U.N. engineer later said the liquid was most likely run-off from the camp kitchen.

The dump site for the human waste was a few hundred yards (meters) away, across the street from the base in shallow, shovel-dug pits next to several homes. Neighbors said the pits often overflow and run to the river. They said they had stopped drinking from the river and sought fresh water uphill.

The AP returned Sunday for a tour with U.N. officials, who acknowledged the facility had undergone a cleanup since then: Septic tanks were emptied, a drainage canal was cleared and the leaky pipe was replaced. The smell of excrement was mostly gone.

Aboveground pipes ran from latrines to a septic tank across a drainage canal that flows to the river. One of the pipes had been repaired. At the bottom of the canal was an area of putrid brown material surrounded by flies that Pugliese said looked like human waste. He said it was not from the base.

Pugliese said the dump site is the responsibility of contractor Sanco Enterprises SA, which runs it under the authority of the local government.

Sanco official Marguerite Jean-Louis said procedures for handling the waste were established by the U.N. and a previous contractor, not her company.

Copyright 2010 The Associated Press.