Test results show origin of the cholera strain but findings yet to confirm where the outbreak started, officials say.
The weather system Tomas has been downgraded from a hurricane to a tropical storm after lashing Haiti with fierce winds and rain, leaving at least six people dead.
The storm spun away from the Turks and Caicos Islands and into the open Atlantic on Saturday, gradually losing steam.
Meanwhile, Haiti still experienced heavy rains after the storm left and authorities warned of the heightened risk of mudslides. Flooding cut off some parts of the country and traffic has been suspended at the airport in the capital, Port-au-Prince.
Officials also warned that the extreme weather could worsen the country’s cholera epidemic, which has killed about 500 people and infected thousands others.
“Dangerous landslides and heavy flooding could still worsen the cholera epidemic. Remain vigilant,” Rene Preval, the president, said.
Much of Haiti’s population of just under 10 million people live in precarious conditions, vulnerable to natural disasters.
“We worry about open sewage now being spread more easily by floodwaters and we worry about people’s access to clean water,” David Daigle from Centres for Disease Control told Al Jazeera.
“All these factors increase the risk for cholera.
“There are 7,000 cases right now and we don’t think we’re at the the peak of the outbreak. We think there will be more cases.”
Marianna Franco, an aid worker, said the Artibonite river has flooded, “which is bad news because it has been particularly affected by cholera”.
The president said a massive aid-distribution effort was being prepared once “the situation on the roads will permit”. The US military has began flights over the country to assess the damage caused by the storm.
The British charity Save the Children said floodwaters in the southern town of Leogane had affected about 35,000 people, turning streets into “rivers,” destroying possessions and washing out tents.
“People here are telling us that they need food and clean water. This town was decimated by the earthquake and it’s essential we get help to these families fast,” Gary Shaye, the Haiti director for the organisation, said.
Thousands of children in Leogane were now at increased risk of diseases like cholera, diarrhea and malaria, he said.
Philippe Joseph, a civil defence official, said that in some parts of the town, the water was three metres deep.
“We are going to have more victims because of the floods and mudslides, but we cannot yet reach the communities most affected,” Joseph said.
Flooding was also reported in the coastal towns of Les Cayes, Jacmel and Gonaives.
In Port-au-Prince, Haitians were up to their ankles in water in some of the many camps where about a million people are sheltering after much of the capital was destroyed and 250,000 people were killed in January earthquake.
But the canvas and tarpaulin shelters appeared to have withstood the storm better than expected, thanks to pre-storm preparations, including hastily dug drainage ditches and sandbag barriers.