Although the outbreak has been contained in two main southern towns, it has spread to other areas, the United Nations said in a statement on Wednesday.

Cholera is transmitted by consumption of contaminated water and food and is linked to poor hygiene, overcrowding and inadequate sanitation. Southern Sudan's infrastructure has been battered by 21 years of civil war. Although a peace treaty ended the fighting more than a year ago, little has improved in the region.

Measures to control the cholera outbreak, including strengthening surveillance and reporting systems and water chlorination are continuing, WHO said.

The outbreak occurred in both southern Sudan's main city of Juba and Yei, near the Ugandan border.

The situation in Yei is "stable and improving daily," with the last case reported on Monday. In Juba the outbreak has been declared officially over, WHO said.