Ebola Mortality Rate

Ebola’s mortality rate may depend on several factors:

  • The particular strain of Ebola.
  • The age and underlying health of the patient.
  • How ill the patient is when s/he begins receiving care.
  • The quality of the care the patient receives.
  • The availability of antibody treatments such as ZMAPP or serum taken from survivors.

Prior Outbreaks

Before this year most Ebola outbreaks have been confined to rural areas, and treatment has been what was feasible in a tent. The West African epidemic is of the Ebola Zaire strain, for which WHO reports mortality rates from prior epidemics ranging from 44% to 90%. [WHO 9/14]

West Africa

It was initially thought that the mortality rate for the West African epidemic was around 55%. [Reuters 8/5/14]  In September, however, a scholarly article in the New England Journal of Medicine calculated the mortality rate in Guinea, Liberia and Sierra Leone at around 70%. [NEJM 9/23/14]  A Sierra Leone study of 44 patients [Reuters 10/29/14] showed 74% overall mortality, but broke the figure down in illuminating ways:

  • 57% of people under age 21 died, compared to 94% of those over the age of 45. Older patients have greater mortality risk.
  • 33% of patients with less than 100,000 copies of the virus per milliliter of blood at diagnosis ultimately died, compared with 94% of those whose had more than 10 million copies per milliliter. As we’ve previously suspected, mortality is highly dependent on how sick a patient is when treatment starts.

A thrilling anecdote from Liberia is also suggestive: A student nurse named Fatu Kekula cared for four household members, and managed to save three of them, achieving a 25% mortality rate. [LA Times 10/6/14]  She avoided infection herself using a resourceful combination of surgical gloves, plastic bags, raincoats and copious amounts of chlorinated water. Critically, she was able to give them IV drips, and she was on call essentially 24/7. What happened to any four patients has no statistical significance, but the demonstration that such a good outcome is even possible is heartening.

Nigeria

Nigeria had an outbreak sparked by a single air traveler from Liberia. Despite many high-risk contacts — and many incidents of quarantine-breaking and other misconduct — in the end there were only 19 cases, of which 7 died, for a mortality rate of just 37%. [WHO c.10/15/14] The number of cases is small, so this figure isn’t too statistically significant. One may speculate, however, that the lower mortality rate in Nigeria reflects two main factors: (1) better quality of health care, and (2) the fact that many patients were being monitored daily, so were presumably given care as soon as they began showing symptoms. The single patient who traveled to Senegal survived, and the child who traveled to Mali died, but neither case tells us anything about overall mortality rates.

The U.S. and Europe

The number of cases treated in western countries is also small, so even less statistically meaningful than the figure for Nigeria. As in Nigeria, most of these patients received treatment as soon as symptoms were noticed, which may be a significant benefit. Disregarding patients still in treatment, the figures, from the excellent New York Times Ebola Facts page, are as follows:

  • United States: 8 patients, of which 1 died and 7 recovered, for a mortality rate of 13%.
  • Europe: 8 patients, of which 3 died and 5 recovered, for a mortality rate of 38%.

Since the figures are so small the difference between Europe and the U.S. could easily be random. But it’s interesting to note that Thomas Eric Duncan, the patient who died in Dallas, had initially been turned away by the hospital, and only started receiving care after he had become so ill that he had to be transported by ambulance. His two nurses, in contrast, began receiving care soon after they first developed fevers, and both have recovered fully. CNN’s discussion of the factors that affect survival in western countries is a bit dated but still worth a look: [CNN 10/20/14]

Dr. Paul Farmer, a Harvard professor and co-founder of the charity Partners in Health, has expressed the hope that with top-notch care the mortality rate for Ebola could be as low as 10%. [London Review of Books 10/23/14] This isn’t inconsistent with the U.S. experience, keeping in mind the low sample number. It will be wonderful if it proves possible to substantially reduce the mortality rate in the African setting. An improved standard of care would not directly help stop the epidemic, but it would indirectly contribute to stopping transmission if it encouraged more people to enter clinics rather than staying at home, which increases the risk of infecting other household members.

Added 10/31/14: Paul Farmer’s emphasis on quality of care implicitly criticizes the way some twenty Ebola outbreaks have been handled since 1976, most notably by Médecins Sans Frontières / Doctors Without Borders (“MSF”). I would characterize the MSF approach as embodying three priorities:

1. Stop the Outbreak, by Isolating Patients.
2. Protect Staff from Getting Infected.
3. Cure as Many Patients as Possible.

For nearly 40 years MSF has been stunningly successful at achieving these goals, often in remote rural settings with extremely limited infrastructure. I’m sure Dr. Farmer would hasten to agree that we owe MSF and its peers an enormous debt of gratitude for their extraordinary service to humanity.

My own view is that MSF’s priorities are correct. Stopping the outbreak must always be job #1. One wants also to minimize risk to staff, but some risk is inevitable and must be accepted in order to end an Ebola outbreak. Curing patients is every doctor’s objective, but if a choice must be made stopping the epidemic is more important. Similarly, if staff start becoming infected at excessive rates we would lose the ability to either stop the outbreak or cure patients.

Saying that these priorities are correct does not, however, answer the question of how much can and should be done to cure patients.

My understanding, for example, is that MSF typically does no blood work apart from an initial test to confirm the diagnosis and final tests to confirm a cure. Often there would be no lab available to do additional testing anyway; it’s difficult and risky for a staff member wearing goggles and three layers of gloves to take a blood sample; puncturing the skin of an Ebola patient can lead to infection and/or uncontrolled bleeding; getting a blood sample takes precious time away from other patients; blood tests would cost money that might be better spent elsewhere; etc. etc. When regular blood tests are available, as in western hospitals, care can be customized to the patient’s individual needs. Infections can be identified and halted; imbalances in electrolytes identified and corrected, etc.

I presume that MSF would agree that a higher standard of care would be desirable, wherever it is feasible. The real question in each situation is where do you strike the balance between an aspiration for the best standard of care and the need to quickly isolate patients to stop the outbreak, as well as constraints of money and infrastructure. It may be that the MSF approach should be implemented quickly as soon as an outbreak is identified, then upgraded as time and resources permit.

Dr. Farmer’s push for a higher standard of care is directly opposed to a recent WHO proposal for “clinics” that would isolate patients but offer little or no medical care. [AP 10/2/14] This is a desperate response to the situation in Monrovia several weeks back where patients were being cared for at home — often infecting many household members — because there were no beds available. Since there now appear to be open beds it may be hoped that we don’t have to do in this inhumane direction, which explicitly sacrifices patient care to the overriding goal of stopping the epidemic.  [Economist 11/1/14]

Antibody Treatments

A handful of U.S. and African patients received the few available doses of ZMAPP, an artificial antibody treatment that has been successfully tested in monkeys. The U.S. patients survived and several of the African patients died, but the numbers are too small to reach any conclusions about its effectiveness. Similarly, several U.S. patients received antibodies in serum taken from survivors. The fact that they survived is encouraging, but again the numbers are too small at this point to support conclusions.

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