GENEVA (Reuters) - The death toll in the world's worst Ebola epidemic has risen to 5,689 out of 15,935 cases reported in eight countries by the end of Nov. 23, the World Health Organization said on Wednesday.

Almost all cases and all but 15 deaths have been in Guinea, Sierra Leone and Liberia - the three hardest-hit countries, which reported 600 new cases in the past week, the WHO said in its latest update.

"The total number of cases reported in Sierra Leone since the outbreak began will soon eclipse the number reported from Liberia," it said. The former British colony has reported 6,599 cases against 7,168 in Liberia.

Transmission of the virus remains intense in Sierra Leone, apart from the southeast, with the capital Freetown still the worst affected area, it said.

"Liberia and Sierra Leone report that fewer than 70 percent of patients are isolated, though there is wide variation among districts," the WHO said.

Peter Piot, a leading specialist on the disease, said on Wednesday that West Africa's Ebola epidemic could worsen further before abating, but that but new infections should start to decline in all affected countries by the end of the year.

(Reporting by Stephanie Nebehay; Editing by Kevin Liffey)