What is the Percentage of Fatality from Ebola ?

Health care workers are among those most at risk of catching Ebola

The Ebola outbreak in West Africa is the world's deadliest to date and the World Health Organization has now declared an international health emergency in response. According to the UN, 961 people have died since February in Guinea, Liberia, Sierra Leone and Nigeria.

Ebola is a viral illness of which the initial symptoms can include a sudden fever, intense weakness, muscle pain and a sore throat, according to the World Health Organization (WHO). And that is just the beginning: subsequent stages are vomiting, diarrhoea and - in some cases - both internal and external bleeding.

The disease infects humans through close contact with infected animals, including chimpanzees, fruit bats and forest antelope.

It then spreads between humans by direct contact with infected blood, bodily fluids or organs, or indirectly through contact with contaminated environments. Even funerals of Ebola victims can be a risk, if mourners have direct contact with the body of the deceased.

  This molecular model shows the parts of the Ebola virus scientists are studying in the hopes of finding drugs that will slow the spread of the disease 

The incubation period can last from two days to three weeks, and diagnosis is difficult. The human disease has so far been mostly limited to Africa, although one strain has cropped up in the Philippines.Healthcare workers are at risk if they treat patients without taking the right precautions to avoid infection. People are infectious as long as their blood and secretions contain the virus - in some cases, up to seven weeks after they recover.

The ebola virus that has killed almost 1,000 people in West Africa this year is fatal for "up to 90%" of those infected, according to the World Health Organization (WHO). But note the words "up to"...What is the normal fatality rate, asks James Fletcher?
The WHO describes ebola as "one of the world's most virulent diseases". It is, according to the organization's website, "a severe, often fatal illness, with a case fatality rate of up to 90%".
A case fatality rate - or CFR - is a relatively simple measurement. It's the number of people diagnosed with an illness divided by the number of people who die because of it. But in the current outbreak, the proportion of infected people dying is far lower than 90%.
"That 90% figure actually comes from one outbreak of ebola which took place in the Congo between 2002 and 2003. It's the highest rate we have ever seen," says Maimuna Majumder, a biostatistician and epidemiologist at the Massachusetts Institute of Technology.

The answer

• Between 60% and 65% of all people known to have been infected with ebola have died
• Different strains of ebola appear to have different fatality rates
• The number of deaths also depends on the quality of treatment
• About 54% of those infected in the current outbreak have died

"The cumulative average considering all ebola cases and deaths from 1976 to the present is actually closer to 60-to-65% and the current outbreak has a CFR of about 54% - though it's subject to change as the outbreak goes on."

This figure of 54%, however, is an average taken from several countries. The fatality rate varies from one country to another - in Guinea it's about 73%, whereas in Liberia its 55%, in Sierra Leone it's 41% and in Nigeria it's 11%.


Why the variation?


The main factors, according to Majumder, are the level of preparedness and the availability and quality of medical care.

Another factor - when it comes to the varying CFR from one outbreak to the next - may be the different strains of the disease. Of the five known ebola strains, the "Zaire" and "Sudan" strains have been responsible for most deaths. The Zaire strain's average fatality rate is 79% and the Sudan strain's is 54% - research on the current outbreak, in Guinea, suggests that it is caused by the Zaire strain.