World Health Organization researchers issued a dire new forecast for the Ebola epidemic Tuesday, one that sees 20,000 cases by November, much sooner than previous estimates. And 70 percent of patients are dying.

That's a big increase over the previous estimates of a 50 percent fatality rate.

“These data indicate that without drastic improvements in control measures, the numbers of cases of and deaths from Ebola virus disease are expected to continue increasing from hundreds to thousands per week in the coming months,” the WHO Ebola Response Team, led by Dr. Christopher Dye, wrote in a report rushed into print by the New England Journal of Medicine.

This projection includes nearly 10,000 people in Liberia alone. WHO said earlier Monday that more than 5,800 people had been infected with Ebola and more than 2,800 had died of it since the virus first broke out in Guinea in December.

And it's likely far worse, especially in Liberia, WHO says. "The true number of deaths will likely never be known, as bodies in the notoriously poor, filthy and overcrowded West Point slum, in the capital, Monrovia, have simply been thrown into the two nearby rivers," WHO said in a separate statement.

But forget about the tales of horrific bleeding from the eyes nose and mouth. Bleeding is one of the most unusual symptoms, the team of experts from around the world said.

Still, it’s looking so bad that Ebola could take permanent hold in West Africa, they said — something that’s never happened before. “For the medium term, at least, we must therefore face the possibility that Ebola virus disease will become endemic among the human population of West Africa,” they said.

“The true case load, including suspected cases and undetected cases, will be higher still."

What could change that? Quick action by the world, the experts said. That means sending more people to track down potential Ebola cases so they can be isolated and treated, providing better hospital treatment and safer burials, and getting better buy-in from the community. In some places, residents still don’t believe Ebola is a virus, and they have attacked and even killed health workers trying to spread the word about the danger.

Patients are also running away and spreading the disease that way.

To stop the epidemic, transmission must be cut in half, they said. “Considering the prospects for a novel Ebola vaccine, an immunization coverage exceeding 50 percent would have the same effect,” they wrote.

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The United States is leading a new response, sending troops and supplies and offering to help coordinate help. WHO and the UN are urging other countries to help. Germany, France, Cuba and China are among countries also sending teams and equipment.

To make the forecast, the team looked at all the available data on the epidemic, which has spread more widely than any previous outbreak of Ebola, in part because it broke out in an area where people travel widely across borders.

It remains clear that close contact with an infected person or their bodily fluids are needed for infection to happen. There’s nothing mysterious about how Ebola spreads, and it's not as easily transmitted as influenza or measles.

Caregivers and health care workers have a high risk. More than 300 health care workers have been infected, and half of them have died.

The most common first symptoms are fever and fatigue. Hemorrhage — the most feared symptom — is seen in fewer than 5 percent of patients, although about 18 percent had unexplained bleeding, the WHO team said.

"There will be more epidemics and outbreaks of Ebola and other new or re-emerging infections."

Ebola has an incubation period of 11 days, and people cannot infect others before they begin to show symptoms — unlike flu, which people can pass along before they even feel ill.

One important number is how many other people each patient infects. It’s different for each country, Dye says — an average of 1.7 in Guinea and 1.8 in Liberia. In Sierra Leone, an infected person sickens two other people on average. Some patients infect many more people than that — than a dozen mourners were infected at the funeral of a single traditional healer who died in Sierra Leone, for instance. And some die or recover without infecting anybody else.

Another important number is what’s called doubling time — how long it takes the number of cases to double. This varies greatly from country to country; in Guinea it’s just under 16 days, in Liberia it’s nearly 23 days and in Sierra Leone it’s 30 days. That’s what leads to the projection of 20,000 cases by Nov. 2. “The true case load, including suspected cases and undetected cases, will be higher still,” the WHO team wrote.

Most of those infected are ages 15 to 44, although people those ages only account for 44 percent of the population in those countries. Older patients are more likely to die, and those who have diarrhea, hemorrhage, difficulty breathing or confusion also seem more likely to die.

Most of those who died succumbed on average four days after they were admitted to a hospital or clinic, and if someone survived, it was usually 11 days before they were better enough to go home, on average. It’s possible that patients who get hospital care live longer, the researchers said, but there’s not enough information to say that for sure.

Patients get vastly different care, depending on where they are treated. Three out of four patients treated in the U.S. have recovered or nearly recovered and the fourth has released little information about his condition. They all got the best possible care, including carefully measured and balanced rehydration, 24-hour nursing care, immaculate conditions and experimental treatments, including drugs and transfusions of blood from patients who have recovered.

In West Africa, some lucky patients get good hospital care that includes saline to replace fluids lost to vomiting and diarrhea, antibiotics to prevent other infections, and pain control. But many are given little more than a bed or a space on the floor, and many are also turned away to die at home or in the streets. So it’s hard to say what will save someone’s life.

“Classic ‘outbreak control’ efforts are no longer sufficient for an epidemic of this size."

The report strongly suggests what doctors is saying is true — there’s nothing unusual about the virus itself, say Dr. Peter Piot of the London School of Hygiene and Tropical Medicine, who helped discovered Ebola, and Dr. Jeremy Farrar of Britain’s Wellcome Trust.

It’s spreading because of dysfunctional health systems, a lack of action by local and international governments and a population that hasn’t caught on immediately to the dangers and what to do about Ebola, they wrote in a commentary in the journal.

“Classic ‘outbreak control’ efforts are no longer sufficient for an epidemic of this size,” they added.

“Rather, what’s required is a large-scale, coordinated humanitarian, social, public health and medical response, combining classic public health measures with safe and effective interventions including behavioral changes, therapies and, when possible, vaccination.”

It will take both a “massive” response and, probably, the use of new treatments and vaccines to control the epidemic, Farrar and Piot wrote.

“But we must also look to the future. There will be more epidemics and outbreaks of Ebola and other new or re-emerging infections,” they added. “Yet our response to such events remains slow, cumbersome, poorly funded, conservative and ill-prepared.”