WHO assistant director-general Dr. Bruce Aylward said the death rate for the outbreak is now estimated at 70 per cent, up from about 50 per cent previously, in the three worst affected countries of Sierra Leone, Guinea and Liberia.
"We will go over 9,000 cases this week," he told reporters from WHO's headquarters in Geneva.
For the last four weeks, there's been 1,000 new cases per week on average. The goal is isolate about 70 per cent of cases within two months to reverse the spread of the outbreak.
The rate of new Ebola cases appears to be slowing down in two districts in Sierra Leone, Kenema and Kailahun, which Aylward attributed to behaviour changes in the community. But he said the virus continues to expand geographically in the worst affected countries.
Modelling projections estimate that by December 2014, 5,000 to 10,000 new Ebola cases per week are anticipated in Guinea, Liberia and Sierra Leone, Aylward said.
To calculate the death rate accurately, officials need to know the true number of cases, which WHO said is substantially under-reported.
The death toll so far in the outbreak, first reported in Guinea in March, has reached 4,447 out of an estimated 8,914 cases thought to be infected.
Risks for health workers
Anthony Banbury, head of the UN Mission for Ebola Emergency Response or UNMEER, said Tuesday the Ebola virus is currently winning the race, but the epidemic can be turned around if treatment and burial teams expand before Dec. 1.
Banbury noted that 300 community treatment centres are needed in the affected countries. In each case, there are a myriad of factors to consider, such as who trains the staff and ensures they are paid, who provides supplies and clean water and who tests patients.
In other news Tuesday, the international aid organization Doctors Without Borders said 16 of its staff members have been infected with the Ebola virus. Of these, nine have died.
Sharon Ekambaram, head of Doctors Without Borders in South Africa, told reporters in Johannesburg that medical workers have received inadequate assistance from the international community.
"Where is WHO Africa? Where is the African Union?" said Ekambaram, who worked in Sierra Leone from August to September. "We've all heard their promises in the media but have seen very little on the ground."
Meanwhile, Facebook CEO Mark Zuckerberg and his wife, Priscilla Chan, said they're donating $25 million US to the CDC Foundation to help address the Ebola epidemic in Guinea, Liberia and Sierra Leone and elsewhere in the world where Ebola is a threat.
Last month, Microsoft co-founder Paul Allen announced a $9-million US donation to the effort.
World Health Organization spokeswoman Dr. Margaret Harris said they're racing to bring in more people and beds but the limited air transport and shipping routes limit the ability to respond.