Jan 1, 2015

Ebola - The (Extreme) Importance of the Case Fatality Rate, CFR
Paul Conton


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.