“In the future, historians will look back and say, ‘Wow, that’s unfortunate,’ ” said Dr. Paul Farmer, co-founder of Partners in Health, a nongovernmental organization that provides health care for the poor. “This unfolded right under the noses of all those NGOs. And they will ask, ‘Why didn’t they try harder? Why didn’t they throw the kitchen sink at cholera in Haiti?’ ”

While the world has dedicated $230 million so far to combating the unexpected epidemic, the United Nations is now pleading for an additional $53.9 million just to get the vulnerable displaced population through the rainy months ahead.

At the same time, Haitian cholera victims are seeking compensation from the United Nations, pressing it to accept responsibility. Early on, protests against the United Nations hindered the construction of treatment centers and the delivery of lifesaving supplies. Now distrust of some cholera programs lingers, and the issue has strained the peacekeepers’ relationship with the Haitians they are protecting in an eight-year-old mission to stabilize the politically volatile nation. So, too, have unrelated allegations that they engaged in criminally abusive behavior.

“In telling the truth, the U.N. could have gained the trust of the population and facilitated the fight against cholera,” said Dr. Renaud Piarroux, who led an early investigation into the outbreak. “But that was bungled.”

The United Nations maintains that an independent panel of experts determined the evidence implicating its troops to be inconclusive.

Questioned for this article, though, those same experts said that Dr. Keim’s work, conducted after their own, provides “irrefutable molecular evidence” that Haiti’s cholera came from Nepal, in the words of G. Balakrish Nair, an Indian microbiologist.

“When you take the circumstantial evidence in our report and all that has come out since, the story now I think is stronger: the most likely scenario is that the cholera began with someone at the Minustah base,” said another expert, Daniele Lantagne, an American engineer, using the French acronym for the United Nations mission.