Ebola
- The (Extreme) Importance of the Case Fatality Rate, CFR by Paul Conton
MSEE
In earlier publications (Ebola
Case Fatality Rate - Another Look) I have attempted to estimate the
Case Fatality Rate, CFR, of Ebola during this West African outbreak.
This
simple little number is particularly important in diseases such as
Ebola, where fatality is high and the optimum treatment is uncertain.
Much can be learnt from an accurate estimation of Ebola CFR in
different situations.
Case Fatality Rate is simply the percentage of Ebola patients who go on
to die from the disease. The WHO estimates (see situation
reports) that the CFR for
hospitalized Ebola patients is 60%, whilst for Ebola sufferers overall
it is 72%. The difference between these two numbers is important. At
the start of the outbreak, the conventional wisdom was that Ebola had
no cure and all that could be offered was treatment of
symptoms. This principally involved administration of well known
medicines to reduce high temperature and pain, and oral rehydration.
The logical conclusion from this was that there would be little
difference in CFR
between hospitalized and non-hospitalized patients. It is believed that
at least partly as a consequence of this, Ebola sufferers saw little
reason to report to hospitals for treatment and the disease spread
quietly within communities. Later in the outbreak, perhaps because of
this realisation,
perhaps because of advances in understanding of treatment options, the
official message changed: Ebola is
curable, but only if you present early at a treatment center.
It's important to accurately measure the institutional CFR and compare
it with the CFR in the overall population. Because if there is no or
little difference in the two then it makes little sense to commit vast
amounts of highly specialized medical resources to the fight against
Ebola. In addition to most of Sierra Leone's medical personnel, we have
teams from Britain, China, Cuba, Nigeria, Italy, the EU, the AU among
others involved in the treatment of Ebola here in Sierra Leone. Are
they making a
difference? Is the CFR much different than it would have been without
this specialized care?
Certainly these patients if left in their
communities would go on to infect others and the outbreak would
continue, so isolation
centers are essential, but do these need to be manned by specialists
with sophisticated medical equipment? How much are we gaining
from treatment by
specialist medical personnel? Could those resources be put to better
use, perhaps in contact tracing and surveillance, areas where there is
abundant evidence of deficiency? This debate has apparently played out
to a stalemate within the
corridors of health power. The US CDC, primarily epidemiologists, have
favoured an approach that involves community care centers, small units
in local communities staffed by non-specialist personnel. The MSF,
dominated by doctors, have favoured an approach with larger treatment
centers, staffed by doctors
and specialists. A compromise has apparently been reached (see community
care vs high-quality treatment) to use a
combination of these approaches. More community care centers are
becoming operational. It will be extremely interesting to get the CFR
figures from these centers.
The
politics of CFR
The Case Fatality Rate is calculated from the number of deaths that
occur within a group of Ebola patients, but once the CFR of a
particular strain of Ebola has been determined, that CFR can then be
used to calculate the number of deaths that have occurred or would
occur. For example, if we know
that there have been 10,000 Ebola
confirmed patients (data for confirmed patients comes from Ebola
testing labs) and we assume or know the CFR in the outbreak is 60%, we
can say with some confidence that at
least 6,000 patients have died
from Ebola during the outbreak (others will have died without going
through lab testing). For political reasons some governments might
prefer not to reveal the full extent of the casualties and would tend
to underestimate the CFR.
Institutional
CFR
The CFR can also be used to compare individual institutions and
different treatment methods. This provides powerful evidence for
improvements at treatment facilities. A recent article in the Guardian
(untested
drug...UK staff leave) indicates that a British medical team walked
out of the Italian
Emergency treatment center because they disagreed with the choice of
drug being used for Ebola treatment. They claimed that the CFR at the
center was above 60%, considerably higher than it should be. In my
previous article I showed that published data indicates that the CFR at
the government-run Hastings Ebola Center, at 32.8%, is almost half the
MSF Ebola CFR. This is
remarkable. Leaders at the highest level have
visited Hastings and have extolled it as a home-grown Sierra Leonean
success. However, doubts have been expressed as to the authenticity of
the published data. If the results are genuine then it
should by now have prompted extensive inquiry into why Hastings'
results are so much better than everywhere else in the subregion. A
halving of CFR means a halving of deaths,
and if this could be replicated elsewhere it would be a huge boost in
the battle to defeat Ebola. Suffice it to say that if the data
is corrupt it would cast a huge question mark over our ability to
successfully prosecute the battle against Ebola.