Case fatality rate

In epidemiology, case fatality rate (CFR) – or sometimes more accurately case-fatality risk – is the proportion of people who have been diagnosed with a certain disease and end up dying of it. Unlike a disease's mortality rate, the CFR does not take into account the time period between disease onset and death. A CFR is generally expressed as a percentage. It is a measure of disease lethality, and thus may change with different treatments.^[1] CFRs are most often used for with discrete, limited-time courses, such as acute infections.

Terminology

The mortality rate – often confused with the CFR – is a measure of the relative number of deaths (either in general, or due to a specific cause) within the entire population per unit of time.^[2] A CFR, in contrast, is the number of deaths among the number of diagnosed cases only, regardless of time or total population.^[3]

From a mathematical point of view, by taking values between 0 and 1 or 0% and 100%, CFRs are actually a measure of

Sometimes the term case fatality ratio is used interchangeably with case fatality rate, but they are not the same. A case fatality ratio is a comparison between two different case fatality rates, expressed as a ratio. It is used to compare the severity of different diseases or to assess the impact of interventions.[6]

Because the CFR is not an

If 100 people in a community are diagnosed with the same disease, and 9 of them subsequently die from the effects of the disease, the CFR would be 9%. If some of the cases have not yet resolved (neither died nor fully recovered) at the time of analysis, a later analysis might take into account additional deaths and arrive at a higher estimate of the CFR, if the unresolved cases were included as recovered in the earlier analysis. Alternatively, it might later be established that a higher number of people were subclinically infected with the pathogen, resulting in an IFR below the CFR.^[citation needed]

A CFR may only be calculated from cases that have been resolved through either death or recovery. The preliminary CFR, for example, of a newly occurring disease with a high daily increase and long resolution time would be substantially lower than the final CFR, if unresolved cases were not excluded from the calculation, but added to the denominator only.

${\displaystyle {\text{CFR in }}{\%}={\frac {\text{Number of deaths from disease}}{\text{Number of confirmed cases of disease}}}\times 100}$^[8]

Infection fatality rate

Like the case fatality rate, the term infection fatality rate (IFR) also applies to

${\displaystyle {\text{IFR in }}{\%}={\frac {\text{Number of deaths from disease}}{\text{Number of infected individuals}}}\times 100}$[8]

Examples

Some examples will suggest the range of possible CFRs for diseases in the real world:

• The CFR for the
  Asian (1957-58) and Hong Kong (1968-69) flus both had a CFR of about 0.2%.^[11][12][13]
• As of 17 Apr 2024,
  coronavirus disease 2019 has an overall CFR of 0.91%, while the CFRs for original SARS and MERS are about 11% and 34%, respectively.^[14][15][16]
• The CFR for yellow fever is about 5-6% (but 40-50% in severe cases).^[17][18][19]
• Legionnaires' disease has a CFR of about 15%.^[20]: 665
• Left untreated,
  septicaemic 45%.^[22][23]
• Active tuberculosis, the infection with the highest mortality rate, has a CFR of 43% in the absence of HIV.^[24][25]
• Ebola virus disease, one of the infections with the highest lethality, has a CFR as high as 90%.^[26]
• Naegleriasis (also known as primary amoebic meningoencephalitis), has a CFR greater than 95%, with a few of the survivors having been treated with heroic doses of amphotericin B and other off-label drugs.^{[citation needed]}
• Rabies has a CFR greater than 99% in unvaccinated individuals.^[27] A few people have survived either by being vaccinated (but after symptoms started, or else later than ideal), or more recently, by being put into a medically induced coma.^{[citation needed]}

See also

• List of human disease case fatality rates
• Mortality rate – Deaths per 1000 individuals per year
• Pandemic severity index – Proposed measure of the severity of influenza

References