Since the hurricane pounded Haiti last week, there has been an uptick of the dangerous disease, according to Stephane De Rengerves, senior executive liaison officer with the International Federation of Red Cross and Red Crescent Societies.
"We don't have official reports yet, but reports from the field show an increase of cases," De Rengerves said.
Cholera, which is spread through water or food contaminated with Vibrio cholerae bacteria, can cause severe diarrhea and vomiting, which leads to extreme dehydration. It can swiftly result in outbreaks, and patients who are not treated quickly can die within hours.
The Saint Antoine Hospital received hundreds of patients over the weekend, most of them suffering injuries from flying debris rather than cholera. But there have been 43 new cases of cholera in the facility, located in Jeremi, which is in Grand-Anse.
Officials said they are out of anesthetics and antibiotics, and haven't gotten any aid, despite the massive damage the Hurricane caused the facility, and aid in the area.
Separately, there at least 100 new cases in Sud. There are 62 cases and 10 deaths in Randel, 30 cases and several deaths in Port-a-Piment, and 11 cases in Les Anglais, according to a source at Pan American Health Organization.
"Quick decisions and strong leadership can make or break relief operations. Right now, 1 million people need urgent humanitarian assistance. Lifesaving measures such as medical aid, clean water and appropriate information should remain the priority at this stage." said Dr. Unni Krishnan, director of Save the Children's Emergency Health Unit in Haiti on Monday in a press release.
"Flooding and contaminated water caused by the storm pose a huge threat to survivors including thousands of children. Clean water and medicine delivered to the hardest hit areas in the next 24 to 48 hours is a key priority."
'Frightening to see from the air'
Vince DeGennaro, a Port-au-Prince-based doctor who is the medical director for the country's only medical emergency helicopter program, has been flying medical relief flights since Thursday into towns along Haiti's devastated southwest coast in the aftermath of the storm.
"These towns on the southwestern coast, it's near total destruction. Just about every building was knocked down, even concrete ones," he said. "It's quite frightening to see from the air."
DeGennaro, who has lived and worked in Haiti since 2012, is medical director of the Haiti Air Ambulance and president of Innovating Health International, a nonprofit that is "dedicated to treating chronic disease and dealing with women's health issues in developing countries."
On Sunday, he flew into the town of Roche-a-Bateau, where he said 90% of the buildings had been destroyed by the storm, including the concrete school and church buildings, leaving the residents with no shelter.
"People are just sleeping outside and that leads to all sorts of problems with disease," he said.
In those conditions, he said, the threat of a cholera outbreak was a "huge concern."
DeGennaro said there had been dozens of cholera deaths in the southwestern town of Port-a-Piment.
Questions over death toll
Matthew wreaked havoc as it made landfall in Haiti on Tuesday, killing hundreds, displacing thousands, destroying homes and knocking out electricity, water supply and communications in the impoverished Caribbean nation.
While international aid workers on the ground say this is the worst disaster to hit Haiti since the 2010 earthquake, it is still unclear how many people may have been killed by the Category 4 storm.
Haiti's official death toll has risen to 372, according to the country's Civil Protection Agency. However, given the strict verification process for victims, the actual numbers are likely much higher. A person is only counted as dead when their identity has been verified by the National Identification Office.
The hardest hit of Haiti's 10 regional departments, Grand-Anse, has reported even more dead than the official national toll. UNICEF said Monday that 475 people had been killed in Grand-Anse, citing local emergency operations authorities who have been tallying the dead from different cities.
DeGennaro said the mayor of Roche-a-Bateau told him that 90 people had been killed in the town alone. DeGennaro said he expected the final death toll to number in the thousands.
The UN Office for the Coordination of Humanitarian Affairs estimates 1.3 million people are living in the hardest hit areas, with 750,000 in need of immediate humanitarian assistance.
Still waiting for help
In Les Cayes, a port city in one of the worst-hit areas, residents told CNN they had yet to receive any government help in their efforts to recover from the disaster.
"I saw the water rising up to my waist. Tin roofs flying everywhere. Then a wall came down behind me," said resident Angelo Joseph as he showed the wreckage of his destroyed home to CNN.
Holly Frew, an emergency communications officer at the disaster relief organization CARE, said the damage in the city was "hard to believe, even as I see it with my own eyes."
"Matthew has uprooted massive trees and plunged them into buildings. Homes are utterly destroyed. And downed power lines litter the streets," she said.
"There are a few glimpses of life as it was -- some markets have re-opened -- but the people here have such a long road ahead."
With roads and bridges washed out, the towns in the southwest have been inaccessible by road for days, and many remained out of reach except by air, said DeGennaro.
"The first challenge has been access to some of these remote communities. We still can't reach some of the most affected areas by car," Marc Vincent, UNICEF's head of mission in Haiti, told CNN.
On the ground, medical staff were finding many patients with soft tissue injuries, lacerations and broken bones from flying debris, said DeGennaro.
Six days after the storm, the wounds were starting to develop serious infections, adding tetanus to the list of medical concerns, he said.
The priority was getting food, water and shelter to affected populations, to try to prevent outbreaks of disease compounding Haiti's misery, he said.
"I expect the cholera to increase and other illnesses related to dehydration in the short term, and malnutrition in the medium term," he said.
On the banks of the River Grande D'Anse, Angela Joseph was one of several women trying to scrub their clothes clean.
During the hurricane, a storm surge swept through the plains and pasture lands on the edge of Jeremie, carrying enormous trees and flipping vehicles and trucks. Joseph's chickens and goats were all killed, and now she has no food for herself and her three children.
Because of the cholera danger, people were cautioned not to drink river water. Women said they've had to buy small plastic bags of water for drinking when they can afford it.
"I haven't eaten all day," Joseph said, as she scrubbed clothes in a plastic bin.