CNN – Medical workers in Haiti on Friday called the upward trend in deaths and illnesses in the cholera outbreak “alarming” as the earthquake-devastated nation’s already strained health system overflowed with the sick.

In the slum of Cite Soleil on the outskirts of Port-au-Prince, Medecins San Frontieres (Doctors Without Borders) saw 216 cases of cholera at Choscal Hospital on Thursday. Five days ago, that number was only 30.

It was expected to be even higher Friday and in the days ahead.

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Stefano Zannini, the head of mission for Medecins Sans Frontieres, said his staff was seeing seven times the cases they were seeing three days ago.

Cholera on the rise in Haiti “The trend is extremely, extremely alarming,” he said. “We have not reached a peak yet but it could arrive next week.”

The death toll climbed Thursday to 796, according to Haiti’s Ministry of Public Health and Population. More than 12,000 people have been sickened.

Epidemiologists predict the outbreak could last for months and say the entire nation of almost 10 million people is at risk because they have no immunity to cholera.

The United Nations warned that Haiti is facing one of the most severe outbreaks of the disease in the past 100 years. It appealed to international donors for almost $164 million in response money and said it anticipates as many as 200,000 people to show symptoms of cholera.

Of grave concern now are confirmed cases that originated in the tent cities of Port-au-Prince, which sprang up to shelter those left homeless by the earthquake last January. Health officials fear that infection could spread quickly in congested, unsanitary conditions and in impoverished neighborhoods where clean drinking water is at a premium.

Symptoms of cholera, an acute, bacterial illness caused by drinking tainted water, can be mild or even non-existent. But sometimes they can be severe: profuse watery diarrhea, vomiting, and leg cramps, which can cause rapid loss of body fluids and lead to dehydration and shock.

If left untreated, a person can die within hours.

Aid workers in Haiti are scrambling as the nation recovers not only from the massive earthquake, but also from last week’s hurricane.

“We are stretched thin,” said Julie Schindall, a spokeswoman for the humanitarian agency Oxfam.

Zannini reminded the world that cholera is as much a logistical problem as a medical one. It’s not just a matter of medical donations or more doctors on the ground, he said. Who will supply clean drinking water? Who will make sure there are proper bathroom facilities? Who will dispose of the waste? Or for that matter, the dead bodies?

“It’s not just about donating money,” Zannini said. “It’s about concrete actions.”