The United Nations says 13 people have died so far in an outbreak of cholera in South Sudan. The first case of cholera was reported in the capital, Juba, on May 15. As of Tuesday, the number of cases was 266. The spokesman for the U.N. secretary-general told reporters Wednesday that humanitarian workers are trying to improve sanitation inside U.N. bases where thousands of civilians have taken refuge since violence erupted in December. Stephane Dujarric says easing the "overcrowded" bases in cities such as Bentiu and Malakal remains a top U.N. priority. Efforts to fight the cholera outbreak also include vaccinating 13,000 people so far in Bentiu. Two cease-fires have been quickly broken by fighting between the South Sudan government and rebels, and the international community fears a humanitarian crisis.