Ebola Case Fatality Rate, CFR -
Another Look by Paul Conton
MSEE
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:
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):