The death toll in Haiti's cholera epidemic climbed on Thursday to 800, according to an American medical expert, but U.S. health authorities said the risk of widespread transmission to the United States was low, given good sanitation there.

Fatalities from the diarrheal disease have risen steadily since the start of the outbreak more than three weeks ago in the poor Caribbean nation, which is struggling to recover from the effects of a devastating January 12 earthquake.

Ezra Barzilay, an epidemiologist at the U.S. Centers for Disease Control and Prevention (CDC), said the emergency in Haiti created by the epidemic was worsening.

"As of November 8, we had about 640 deaths. Today we are at 800," he said in a call from Haiti to participants at a medical conference in Biloxi, Mississippi.

"The situation here is more dire every day. Haitians are in line (for treatment). Hospital beds are gone. Hospitals are completely overrun," he said, adding local medical staff were being forced into choices over which patients they treated.

Haiti's health ministry said on Thursday that up to Tuesday, November 9, confirmed deaths from cholera totaled 724, with 11,125 hospitalized cases registered. Ten deaths had been recorded in the capital Port-au-Prince, where authorities fear contagion in crowded camps housing earthquake survivors.

Neighboring Dominican Republic was on high alert to prevent possible transmission. In the United States, just two hours flying time away from Haiti, authorities said there was a possibility of a few cholera cases emerging through travel links. But the risk of widespread transmission was low.

"Good sanitation which includes plumbing, separation of fecal wastes and similar measures, and access to safe drinking water in the United States would work against widespread transmission," CDC spokesman David Daigle told Reuters.

On its website, the Florida Department of Health said travel to and from Haiti had increased since the Haitian earthquake with travelers including relief workers and local Haitian residents visiting family in Haiti.

"Cholera does not spread easily in developed countries such as the U.S., but we want to be sure we do not miss any high-risk situations, like cholera in a food-handler, or clusters or outbreaks," the department said.

Florida has some 241,000 Haitian-born residents, 46 percent of the Haitian-born population in the United States.

Haiti's epidemic, which experts believe was worsened by flooding caused by Hurricane Tomas this month, has piled another humanitarian emergency on the Western Hemisphere's poorest state, whose capital was wrecked by the January earthquake that killed more than 250,000 people.

Presidential and legislative elections scheduled for November 28 in the Caribbean nation are set to go ahead.

(Reporting by Joseph Guyler Delva in Port-au-Prince, Leigh Coleman in Biloxi, Maggie Fox in Washington; Editing by Pascal Fletcher and Xavier Briand)