The World Health Organization says more than 700 more Ebola cases emerged in West Africa in one week, a statistic that shows the outbreak is accelerating.

Just three weeks ago the number of new cases was around 500 for a one-week period. The number of people believed to have killed is now more than 2,600, an increase of roughly 200 from the last estimate, WHO said Thursday. Most deaths have been in Liberia.

The new figures from the U.N. health agency show that the disease is thought to have sickened more than 5,300 people. Just under half of those cases were recorded in the last three weeks.

Some 318 health care workers have been sickened, and about half have died.

The outbreak has struck Liberia, Sierra Leone, Guinea, Nigeria and Senegal.