Dec 21, 2014

Ebola Case Fatality Rate, CFR - Another Look
Paul Conton

I wrote an article in September this year (see Ebola - What is the True Case Fatality Rate) in which I calculated the Case Fatality Rate of Ebola in selected institutions to be between 50% and 72% based on published statistics for those institutions. The WHO in its most recent situation reports has been giving an institutional CFR of 60% and an overall regional CFR of 72%, although it has not outlined the methodolody for arriving at these precise figures. Our Sierra Leone Ministry of Health and Sanitation on the other hand, in its most recent situation report is claiming a national Ebola CFR of 31.2%.

One could perhaps make the argument that the SLMOHS's figures have been distorted by very poor data in the early stages of the outbreak, when record keeping was poor or non-existent. Turning to individual institutions, the SLMOHS figures for the Hastings Ebola Treatment Center, which opened later in the outbreak, in September, are:

Current admissions:         54
Cumulative admissions:   679
Cumulative deaths          205
Cumulative discharges     420

So far so good! The current admissions plus cumulative deaths plus cumulative discharges add up exactly to the cumulative admissions, as one might expect.

Ignoring the current admissions, whose outcomes are yet to be determined, these numbers give a Case Fatality Rate of (205/625)*100, or 32.8%. The CFR of Hastings Ebola Center is approximately half the WHO figure for institutional CFR!

Now, turning to MSF, which has treated a large number of Ebola patients in West Africa, its Ebola website tells us that of the patients it has admitted to its various centers since the beginning of this outbreak, "
4,400 were confirmed as having Ebola. Nearly 1,900 patients have survived."

Unfortunately, it does not tell us how many are currently admitted, but since these are cumulative figures nine months into the outbreak, the current admissions will be a relatively small percentage of the cumulative (compare the Hastings example above). Thus, with this small error (leading to an underestimation of CFR):

    Overall (regional) MSF Ebola CFR = (4,400-1900)x100/4400 = 56.8%