The International Rescue Committee's Aisha Bain says the infection risk is "very great"Five cases of Cholera have been detected in Haiti's capital, Port-au-Prince, the UN says, amid an outbreak that has killed more than 200 people.
UN spokeswoman Imogen Wall told the Reuters news agency the cases had been quickly diagnosed and isolated.
She said they had been infected in the main outbreak zone - the Artibonite region - and had subsequently travelled to the capital, where they fell ill.
This meant Port-au-Prince was "not a new location of infection", she noted.
Earlier, Ms Wall said the prospect of cholera in the city, where more than a million survivors of January's earthquake are living in tents, was "awful".
Those in the camps are highly vulnerable to the intestinal infection, which is caused by bacteria transmitted through contaminated water or food.
Cholera causes diarrhoea and vomiting leading to severe dehydration, and can kill quickly if left untreated though rehydration and antibiotics.
'No safety cordon'
With 2,674 cases of the disease reported, health officials have been trying to contain the outbreak in Artibonite and Central Plateau.
They said they had stepped up disease prevention measures and surveillance at the tent camps, and sent medical teams north to treat those infected so they did not travel to the capital to seek help.
Ms Wall said officials were also identifying sites in Port-au-Prince for tent clinics, where patients could be treated away from other people.
"If we have cases in Port-au-Prince, the only way to contain them is to isolate them," she said. "Obviously, preventing the disease spreading to the city is an absolutely paramount concern right now."
Earlier on Saturday, the chairman of the US-based charity, Board of Trustees of Food for the Poor, warned that the Haitian authorities and international organisations had not moved quickly enough to contain the outbreak.
"Right now, it's been over 72 hours. There is no safety cordon," Daniel Rouzier told Reuters. "If the sick had the proper healthcare where they were, they wouldn't have come to this chaotic city."
"There is still time to react. If the proper actions are taken, I think we will be able to limit the number of people who die."
Overwhelmed
Meanwhile, officials confirmed that 194 people had died of cholera in Artibonite, and another 14 in Central Plateau.
The worst-hit areas were Douin, Marchand Dessalines and areas around Saint-Marc, about 100km (60 miles) north of Port-au-Prince. But a number of cases have also been reported in the city of Gonaives, and towns closer to the capital, including Archaei, Limbe and Mirebalais.
Local hospitals have been overwhelmed. Aid workers said many patients at the St Nicholas hospital in Saint-Marc were being forced to lie outside in the car park in unhygienic conditions, hooked up to intravenous drips.
Dr Jhonny Fequiere told the BBC that his hospital in Marchand Dessalines was also struggling to cope, and that he had seen dozens die.
"We are trying to take care of people, but we are running out of medicine and need additional medical care. We are giving everything we have but we need more to keep taking care of people," he said.
Some patients said they became ill after drinking water from a canal, but others said they were drinking only purified water. The Artibonite river, which irrigates central Haiti, is thought to be contaminated.
Haitian Health Minister Alex Larsen has urged people to wash their hands with soap, not eat raw vegetables, boil all food and drinking water, and avoid bathing in and drinking from rivers.
There are enough antibiotics in Haiti to treat 100,000 cases of cholera and intravenous fluids to treat 30,000, according to the UN.
This is the first time in a century that cholera has struck Haiti.
