What Is the Ebola Virus's Survival Rate? And Other Key Questions About the Epidemic

The first case of Ebola has been diagnosed in the United States.

For the first time ever, doctors have diagnosed a case of the Ebola virus in a U.S. patient, the Centers for Disease Control and Prevention confirmed Tuesday.

The patient was diagnosed on Sunday and is now in isolation at the Texas Health Presbyterian Hospital of Dallas. The patient came to the U.S. earlier this month from Liberia—one of several West African nations where the disease has raged for months.

Previously, four patients who already had been diagnosed with Ebola were intentionally brought to the U.S. for treatment, but this patient represents the first case to be discovered in the U.S. Here are key facts about the Ebola virus:

1. What is the Ebola virus's survival rate?

The average Ebola survival rate is about 50 percent, according to the World Health Organization, but it varies greatly, in part because of the different medical resources available to treat different patients.

In past outbreaks, all of which have been in Africa, fatality rates ranged from 25 percent to 90 percent.

The actual survival rate in the current outbreak in West Africa could be far lower, as many cases have gone unreported. American Ebola survivor Kent Brantly said his clinic in Liberia had only one survivor in a month and a half of treating patients.

Among patients treated in the U.S., the survival rate is 100 percent so far. Previously, four patients already diagnosed with Ebola had been taken to the U.S. for emergency care. Two were treated and released from Emory University Hospital, one was treated and released from Nebraska Medical Center in Omaha, and a fourth is currently in treatment at Emory. A fifth American who was exposed to the disease in Sierra Leone was brought to the National Institutes of Health this week for monitoring and participation in a research study.

2. Is there a cure for Ebola?

No. The first people treated for Ebola inside the U.S. lived, but no one knows exactly why. A few drugs are being developed and have been used, but we don't know whether they worked or simpler interventions did the job on their own. There's also no vaccine, though one is being tested by the National Institutes of Health. Officials didn't say whether the U.S. patient would receive an experimental medicine.

3. What is the incubation period for Ebola?

The incubation period for Ebola can span anywhere from two to 21 days. Symptoms most often begin to appear eight to 10 days after exposure.

4. How does Ebola spread?

Ebola is not airborne. It is spread through bodily fluids, and patients are contagious only while they're displaying symptoms.

5. What are the disease's symptoms?

The early signs of Ebola can be similar to flu-like symptoms, including: fever, severe headaches, general weakness, vomiting, diarrhea, and unexplained bruising or bleeding. In its later stages, according to the NIH, the disease causes a severe rash; bleeding from the eyes, nose, mouth, and rectum; and death.

6. How broad is the outbreak in Africa?

According to data from the World Health Organization, more than 6,574 cases of Ebola have been reported in Africa, with 3,091 people confirmed dead from the virus as of Sept. 23, though health officials say the actual total is likely far higher. The majority of the cases have been in Liberia, where there are 3,458 confirmed, probable, and suspected cases, with 1,830 deaths. The vast majority of the other cases have been in Sierra Leone (2,021 cases, 605 deaths) and Guinea (1,074 cases, 648 deaths). There were 20 cases reported in Nigeria, including eight deaths, and one reported case in Senegal.

The outbreak is six months old. The CDC issued its first announcement of an Ebola outbreak in Guinea on March 25, reporting that there had already been 86 suspected cases and 59 deaths.

7. Is this the worst outbreak ever?

Yes. There have already been nearly three times as many cases reported since March than in all other Ebola outbreaks combined. There were 2,361 reported cases of Ebola in all prior outbreaks since the disease was discovered in 1976. Prior to the current epidemic, the outbreak with the most cases occurred in Uganda from 2000 to 2001. There were 425 reported cases, with 224 deaths, a 53 percent mortality rate.

The CDC has predicted that the number of infections in the current outbreak could grow to 1.4 million by Jan. 20 if the outbreak is not brought under control. WHO predicts the number of cases will reach 20,000 by the beginning of November.

8. Why is this outbreak so much worse?

Although Ebola has been around since the 1970s, past outbreaks have "burned out" quickly because they happened in remote areas. The current West African outbreak marks the first time the virus has spread through populated cities, and the porous borders among countries helped its spread. This is also the first time Ebola has presented in West African countries, which are unfamiliar with the virus and unequipped to deal with it. Widespread superstition, misunderstanding, and fear of the disease has contributed to its rapid spread, and the countries' weak health infrastructures have been unable to contain it.

9. What is the U.S. doing about the African outbreak?

An estimated 3,000 U.S. forces will eventually be involved in helping to control the Ebola epidemic, according to the White House. A Joint Force Command center has been set up in Monrovia, Liberia, to "provide regional command and control support to U.S. military activities and facilitate coordination with U.S. government and international relief efforts." Military personnel have already begun their work in Liberia; Major Gen. Darryl Williams, who is in charge of Operation United Assistance, said Monday that he has 175 soldiers currently in Liberia, and 30 stationed in surrounding areas setting up logistics.

President Obama said teams are working to set up an air bridge with Senegal, to move supplies and aid workers into the affected areas. The U.S. is also setting up a field hospital and a training facility to train health workers from around the globe; build new treatment centers; and distribute hundreds of thousands of information kits and supplies to families in the region.

CORRECTION: A previous version of this story said the survival rate in past Ebola outbreaks was between 25 and 90 percent.

1. What is the Ebola virus's survival rate?

The average Ebola survival rate is about 50 percent, according to the World Health Organization, but it varies greatly, in part because of the different medical resources available to treat different patients.

In past outbreaks, all of which have been in Africa, fatality rates ranged from 25 percent to 90 percent.

The actual survival rate in the current outbreak in West Africa could be far lower, as many cases have gone unreported. American Ebola survivor Kent Brantly said his clinic in Liberia had only one survivor in a month and a half of treating patients.

Among patients treated in the U.S., the survival rate is 100 percent so far. Previously, four patients already diagnosed with Ebola had been taken to the U.S. for emergency care. Two were treated and released from Emory University Hospital, one was treated and released from Nebraska Medical Center in Omaha, and a fourth is currently in treatment at Emory. A fifth American who was exposed to the disease in Sierra Leone was brought to the National Institutes of Health this week for monitoring and participation in a research study.

2. Is there a cure for Ebola?

No. The first people treated for Ebola inside the U.S. lived, but no one knows exactly why. A few drugs are being developed and have been used, but we don't know whether they worked or simpler interventions did the job on their own. There's also no vaccine, though one is being tested by the National Institutes of Health. Officials didn't say whether the U.S. patient would receive an experimental medicine.

3. What is the incubation period for Ebola?

The incubation period for Ebola can span anywhere from two to 21 days. Symptoms most often begin to appear eight to 10 days after exposure.

4. How does Ebola spread?

Ebola is not airborne. It is spread through bodily fluids, and patients are contagious only while they're displaying symptoms.

5. What are the disease's symptoms?

The early signs of Ebola can be similar to flu-like symptoms, including: fever, severe headaches, general weakness, vomiting, diarrhea, and unexplained bruising or bleeding. In its later stages, according to the NIH, the disease causes a severe rash; bleeding from the eyes, nose, mouth, and rectum; and death.

6. How broad is the outbreak in Africa?

According to data from the World Health Organization, more than 6,574 cases of Ebola have been reported in Africa, with 3,091 people confirmed dead from the virus as of Sept. 23, though health officials say the actual total is likely far higher. The majority of the cases have been in Liberia, where there are 3,458 confirmed, probable, and suspected cases, with 1,830 deaths. The vast majority of the other cases have been in Sierra Leone (2,021 cases, 605 deaths) and Guinea (1,074 cases, 648 deaths). There were 20 cases reported in Nigeria, including eight deaths, and one reported case in Senegal.

The outbreak is six months old. The CDC issued its first announcement of an Ebola outbreak in Guinea on March 25, reporting that there had already been 86 suspected cases and 59 deaths.

7. Is this the worst outbreak ever?

Yes. There have already been nearly three times as many cases reported since March than in all other Ebola outbreaks combined. There were 2,361 reported cases of Ebola in all prior outbreaks since the disease was discovered in 1976. Prior to the current epidemic, the outbreak with the most cases occurred in Uganda from 2000 to 2001. There were 425 reported cases, with 224 deaths, a 53 percent mortality rate.

The CDC has predicted that the number of infections in the current outbreak could grow to 1.4 million by Jan. 20 if the outbreak is not brought under control. WHO predicts the number of cases will reach 20,000 by the beginning of November.

8. Why is this outbreak so much worse?

Although Ebola has been around since the 1970s, past outbreaks have "burned out" quickly because they happened in remote areas. The current West African outbreak marks the first time the virus has spread through populated cities, and the porous borders among countries helped its spread. This is also the first time Ebola has presented in West African countries, which are unfamiliar with the virus and unequipped to deal with it. Widespread superstition, misunderstanding, and fear of the disease has contributed to its rapid spread, and the countries' weak health infrastructures have been unable to contain it.

9. What is the U.S. doing about the African outbreak?

An estimated 3,000 U.S. forces will eventually be involved in helping to control the Ebola epidemic, according to the White House. A Joint Force Command center has been set up in Monrovia, Liberia, to "provide regional command and control support to U.S. military activities and facilitate coordination with U.S. government and international relief efforts." Military personnel have already begun their work in Liberia; Major Gen. Darryl Williams, who is in charge of Operation United Assistance, said Monday that he has 175 soldiers currently in Liberia, and 30 stationed in surrounding areas setting up logistics.

President Obama said teams are working to set up an air bridge with Senegal, to move supplies and aid workers into the affected areas. The U.S. is also setting up a field hospital and a training facility to train health workers from around the globe; build new treatment centers; and distribute hundreds of thousands of information kits and supplies to families in the region.

CORRECTION: A previous version of this story said the survival rate in past Ebola outbreaks was between 25 and 90 percent.