After studying molecular data known as full genome sequencing on the strain of cholera found in Haiti - and that prevalent in Nepal in 2010 - Dr Lantagne said: "We now know that the strain of cholera in Haiti is an exact match for the strain of cholera in Nepal."
Mountain of claims
In 2011 Dr Lantagne was employed by the UN as one of a "Panel of Experts" tasked with looking into the outbreak.
The 2011 UN report - co-signed by her - acknowledged that inadequate toilets in the Nepalese UN camp in the mountain town of Mirabalais could have leaked the cholera virus into the nearby Meye River which flows into the country's main waterways.
But the report stressed that the outbreak "was not the fault" of any "group or individual".
The Panel of Experts added that the subsequent spread of the disease across Haiti was due to many factors - including the country's deeply inadequate water supply and almost non-existent sewage disposal systems.
Now, Dr Lantagne says the new genome data (in addition to other evidence) has changed her view since she had co-authored the UN report which effectively said no-one was to blame.
"We can now say," Dr Lantagne said, "that the most likely source of the introduction of cholera into Haiti was someone infected with the Nepal strain of cholera and associated with the United Nations Mirabalais camp."
The UN's Head of Humanitarian Affairs in Haiti, Nigel Fisher, acknowledged the new information but said he could not comment on its substance.
"I know there's new information there," Mr Fisher said.
"But the investigation is still with the [UN's New York] legal office, so I'm not able to say anything at this time until that's gone through the due process."
Mr Fisher sought to stress, however, the work the UN was doing to mitigate the effects of the cholera.
"What I can tell you about is the work I'm co-ordinating to respond to that terrible epidemic and the fact that we've seen a significant decline in cases over the last year. If we take any encouragement, we take encouragement from that."
The UN's lawyers are facing a mass compensation claim being pursued by Haitian and US lawyers against the UN.