epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evi ...

, case fatality rate (CFR) – or sometimes more accurately case-fatality risk – is the proportion of people diagnosed with a certain disease, who end up dying of it. Unlike a disease's

mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of d ...

, the CFR does not take into account the time period between disease onset and death. A CFR is generally expressed as a percentage. It represents a measure of disease

lethality Lethality (also called deadliness or perniciousness) is how capable something is of causing death. Most often it is used when referring to diseases, chemical weapons, biological weapons, or their toxic chemical components. The use of this ter ...

and may change with different treatments. CFRs are most often used for with discrete, limited-time courses, such as acute

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

Terminology

The ''

'' – 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 of

risk In simple terms, risk is the possibility of something bad happening. Risk involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environm ...

(case fatality risk) – that is, they are a proportion of incidence, although they don't reflect a disease's incidence. They are neither rates,

incidence rate In epidemiology, incidence is a measure of the probability of occurrence of a given medical condition in a population within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time p ...

s, nor

ratio In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...

s (none of which are limited to the range 0–1). They do not take into account time from disease onset to death. 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. Because the CFR is not an

by not measuring frequency, some authors note that a more appropriate term is case 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 = \frac\text\text\times100

Infection fatality rate

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

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

s, but represents the proportion of deaths among all infected individuals, including all

asymptomatic In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered a ...

and 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 have ''inapparent'', ''silent'' or ''subclinical'' infections and may inadvertently infect others. By definition, the IFR cannot exceed the CFR, because the former adds asymptomatic cases to its denominator.

\text = \frac\text\text\times100

Examples

A half dozen examples will suggest the range of possible CFRs for diseases in the real world: * The CFR for the Spanish (1918) flu was >2.5%, about 0.1% for the Asian (1956-58) and Hong Kong (1968-69) flus, and <0.1% for other influenza pandemics. *

Legionnaires' disease Legionnaires' disease is a form of atypical pneumonia caused by any species of '' Legionella'' bacteria, quite often ''Legionella pneumophila''. Signs and symptoms include cough, shortness of breath, high fever, muscle pains, and headaches. Na ...

has a CFR of about 15%. * The CFR for

yellow fever Yellow fever is a viral disease of typically short duration. In most cases, symptoms include fever, chills, loss of appetite, nausea, muscle pains – particularly in the back – and headaches. Symptoms typically improve within five days. ...

is estimated to be around 5-6% (40-50% for severe cases, which make up around 12% of all cases). *

Bubonic plague Bubonic plague is one of three types of plague caused by the plague bacterium ('' Yersinia pestis''). One to seven days after exposure to the bacteria, flu-like symptoms develop. These symptoms include fever, headaches, and vomiting, as wel ...

, left untreated, will have a CFR of as much as 60%. With antibiotic treatment, the CFR for

septicaemic plague Septicemic plague is one of the three forms of plague, and is caused by '' Yersinia pestis'', a gram-negative species of bacterium. Septicemic plague is a systemic disease involving infection of the blood, and is most commonly spread by bites fr ...

is 45%, pneumonic 29% and bubonic 17%. * Zaïre Ebola virus is among the deadliest viruses with a CFR as high as 90%. *

Naegleriasis Naegleriasis (also known as primary amoebic meningoencephalitis; PAM) is an almost invariably fatal infection of the brain by the free-living unicellular eukaryote ''Naegleria fowleri''. Symptoms are meningitis-like and include headache, fever ...

(also known as primary amoebic meningoencephalitis), caused by the unicellular ''

Naegleria fowleri ''Naegleria fowleri'', colloquially known as a "brain-eating amoeba", is a species of the genus ''Naegleria'', belonging to the phylum Percolozoa, which is technically not classified as true amoeba, but a shapeshifting amoeboflagellate excava ...

'', has a case fatality rate greater than 95%. *

Rabies Rabies is a viral disease that causes encephalitis in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, ...

virus has a CFR of 99 to 100% in unvaccinated individuals.

References

External links