An Ebola outbreak in the Democratic Republic of?Congo has killed more than 400 people and is still spreading, with a first case reported in the major city of Kisangani nearly 600 kilometers from its epicenter.

The highly infectious disease has claimed 438 lives among the 1,406 people confirmed infected — a fatality rate of just over 31% — since the outbreak was declared on May 15, the National Institute of Public Health (INSP) said in its latest report published on Thursday.

The center of the outbreak — whose true scale remains difficult to assess — was in the northeastern Ituri province, where more than 83% of the deaths have occurred.