A U.N. panel investigating the source of Haiti’s 2010 cholera outbreak has turned up circumstantial evidence suggesting that U.N. peacekeepers may have introduced a lethal strain of the disease into the Haitian population in the fall, triggering an epidemic that has so far killed more than 4,500 people and sickened another 300,000.

But the panel stopped short of blaming the blue-helmeted forces for causing the cholera outbreak, saying that the elements contributing to the spread of the disease — including poor sanitation and a dysfunctional health care system — were so varied as to make it impossible to identify a specific culprit.

“The independent panel concludes that the Haiti cholera outbreak was caused by the confluence of circumstances . . . and was not the fault of, or deliberate action of, a group or individual,” according to the 32-page panel report, which was released late Wednesday.

U.N. peacekeeping officials highlighted the inconclusive findings to underscore that there was no hard evidence linking the U.N. peacekeeping mission to the cholera outbreak. The United Nations will establish a task force to study the findings and recommendations, including a call for pre-screening of U.N. peacekeepers for cholera, said Martin Nesirky, the spokesman for U.N. Secretary General Ban Ki-moon.

In October, the infectious cholera bacterium made its first appearance in Haiti in nearly a century, striking its first victims near a U.N. outpost in Mirebalais, a town on the Meye tributary of the Artibonite River. Cholera causes severe, dehydrating diarrhea that can kill children and adults in less than 12 hours.

Within days, the disease had spread throughout the river delta to the coast, infecting thousands of Haitians in riverside towns along the way. It has since extended throughout the country and continues to claim lives.

Haitians and public health experts elsewhere soon suspected that U.N. peacekeepers had contaminated the river. A Nepalese force arrived at Mirebalais between Oct. 8 and Oct. 24, the same period the first cholera deaths were first recorded.

In December, Ban commissioned an independent panel to “investigate and seek to determine the source” of the cholera outbreak.

The four-member team concluded that the cholera strain came from South Asia, possibly Nepal, and that it was probably introduced by human activity around the U.N. base along the Meye tributary. The panel also cited a poorly constructed sewage system at the U.N. camp, which allowed human feces and other waste to flow into the tributary.

“The evidence overwhelmingly supports the conclusion that the source of the Haiti cholera outbreak was due to contamination of the Meye Tributary of the Artibonite River with a pathogenic strain of current South Asian type Vibrio cholarae as a result of human activity,” the panel wrote in its report.

The Nepalese troops arrived in Haiti shortly after completing three months of training in Kathmandu, Nepal, and a medical exam; the panel does not say whether they were screened for cholera.

The panel dismissed an earlier study by a French epidemiologist, Renaud Piarroux, who concluded that the outbreak was introduced into Haiti by an infected U.N. soldier, saying that he had not provided sufficient evidence to support his case. The panel also noted that U.N. medical records show no evidence that Nepalese peacekeepers had shown signs of illness before or during the outbreak.

Peacekeepers from other countries, including a contingent of 60 Bangladeshi policemen posted at Mirebalais, were also deployed in the area.

“The precise country from where the Haiti isolate of Vibrio cholerae arrived is debatable,” the panel stated. But the “initial genetic analysis” indicates striking similarities with strains found in South Asia, including Nepal. One set of genetic tests examining mutations in cholera gene samples indicated that “the strains isolated in Haiti and Nepal during 2009 were a perfect match.”

The panel also found that the “sanitation conditions” at the U.N. camp in Mirebalais “were not sufficient to prevent contamination of the Meye Tributary System with human fecal waste.” The timeline of the cholera’s spread, which struck communities throughout the delta in a matter of days, “is consistent with the epidemiological evidence indicating that the outbreak began in Mirebalais and within two to three days cases were being seen throughout the Artibonite River Delta.”

But Michel Bonnardeaux, a spokesman for the U.N. peacekeeping department, said the report presents no “conclusive scientific evidence linking the outbreak to the [U.N.] peacekeepers or to the Mirebalais camp.” Bonnardeaux added, “Anyone carrying the relevant strain of the disease in the area could have introduced the bacteria into the river.”

Indeed, the panel decided to give the United Nations, and the Nepalese, the benefit of the doubt, saying, “The introduction of this cholera strain as a result of environmental contamination with feces could not have been the source of such an outbreak without simultaneous water and sanitation and health care deficiencies. These deficiencies, coupled with conducive environmental and epidemiological conditions, allowed the spread of the Vibrio cholerae organism in the environment, from which a large number of people became infected.

In the end, the panel echoed the U.N.’s main talking point throughout the cholera crisis: The battle to end the scourge should take priority over determining how it got there. “The source of cholera in Haiti is no longer relevant to controlling the outbreak,” the report concluded. “What are needed at this time are measures to prevent the disease from becoming endemic.”