Doctors Without Borders said the group's five cholera treatment centers had at least 457 patients Monday. There were 500 patients Tuesday.
Spokesman Mathieu Fortoul said the number of cholera patients had since dropped, with the group's clinics having about 430 patients Friday.
The increase in cases was anticipated. Cholera spreads through water, and Haiti has seen a spike in the number of cases following periods of heavy rainfall. The country is vulnerable in large part because it doesn't have proper sanitation and sewage systems.
Cholera, an intestinal infection caused by the bacterium Vibrio cholera, has sickened more than 600,000 people and killed more than 7,500 others in Haiti since it surfaced several months after the devastating 2010 earthquake, health officials say.
Many people have attributed the disease's introduction to a unit of U.N. peacekeepers from Nepal, where the disease is endemic.
Haiti was spared a direct hit from Hurricane Sandy when it passed to the west the night of Oct. 24, but heavy rain in the storm's outer bands pounded the south and capital for several days.
Officials say at least 54 people died, more than any other Caribbean country. The storm also destroyed 70 percent of the crops in southern Haiti and caused
The rainfall compounded the misery for the some 370,000 people still living in flimsy shelters as a result of the earthquake.