Case fatality rate

Not to be confused withmortality rate.

Inepidemiology,case fatality rate(CFR) – or sometimes more accuratelycase-fatality risk– is the proportion of people who have beendiagnosedwith a certain disease and end updying of it.Unlike a disease'smortality 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 diseaselethality,and thus may change with differenttreatments.CFRs are most often used for with discrete, limited-time courses, such as acuteinfections.

Terminology

Themortality 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.A CFR, in contrast, is the number of deaths among the number of diagnosed cases only, regardless of time or total population.

From a mathematical point of view, by taking values between 0 and 1 or 0% and 100%, CFRs are actually a measure ofrisk(case fatality risk) – that is, they are aproportion of incidence,although they do not reflect adisease's incidence.They are neitherrates,incidence rates,norratios(none of which are limited to the range 0–1). They do not take into account time from disease onset to death.

Sometimes the termcase fatality ratiois used interchangeably withcase 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.

Because the CFR is not anincidence rateby not measuring frequency, some authors note that a more appropriate term iscase fatality proportion.

Example calculation

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.

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.

${\text{CFR in }}{\%}={\frac {\text{Number of deaths from disease}}{\text{Number of confirmed cases of disease}}}\times 100$

Infection fatality rate

Like the case fatality rate, the terminfection fatality rate(IFR) also applies toinfectious diseases,but represents the proportion of deaths among all infected individuals, including allasymptomaticand undiagnosed subjects. It is closely related to the CFR, but attempts to additionally account for inapparent infections among healthy people.The IFR differs from the CFR in that it aims to estimate the fatality rate in both sick and healthy infected: the detected disease (cases) and those with an undetected disease (asymptomatic and not tested group).Individuals who are infected, but show no symptoms, are said to haveinapparent,silentorsubclinicalinfections and may inadvertently infect others. By definition, the IFR cannot exceed the CFR, because the former adds asymptomatic cases to its denominator.

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

Examples

Main article:List of human disease case fatality rates

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

• The CFR for theSpanish (1918) fluwas greater than 2.5%, while theAsian (1957-58)andHong Kong (1968-69) flusboth had a CFR of about 0.2%.
• As of 24 Nov 2024,coronavirus disease 2019has an overall CFR of 0.91%, although the CFRs of earlier strains of COVID-19 was around 2%, the CFRs for originalSARSandMERSare about 11% and 34%, respectively.
• The CFR foryellow feveris about 5-6% (but 40-50% in severe cases).
• Legionnaires' diseasehas a CFR of about 15%.
• Left untreated,bubonic plaguewill have a CFR of up to 60%.With antibiotic treatment, the CFR for bubonic plague is 17%,pneumonic29% andsepticaemic45%.
• Activetuberculosis,the infection with the highest mortality rate, has a CFR of 43% in the absence ofHIV.
• Ebola virus disease,one of the infections with the highest lethality, has a CFR as high as 90%.
• Naegleriasis(also known as primary amoebic meningoencephalitis), has a CFR greater than 95%, with a few of the survivors having been treated withheroic dosesof amphotericin B and otheroff-label drugs.
• Rabieshas a CFR greater than 99% in unvaccinated individuals.A few people have survived either by being vaccinated (butafter symptoms started, or else later than ideal), or more recently, by being put into a medically induced coma.

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

External links

• Definitions of case fatality for coronary events in the WHO MONICA Project
• Swine flu: what do CFR, virulence and mortality rate mean?