# Case Fatality Rate (CFR)

\keɪs\ \fəˈtælɪti\ \reɪt\ \(si-ɛf-ɑr)\

In epidemiology, the Case Fatality Rate of a disease is the percentage of known cases of a disease that cause the patient to die. It is equal to the number of people known to have died from the disease divided by the number of known cases of people having the disease. In other words, the numerator is the total number of people *known to have died from the disease*. The denominator is the total number of *known cases of the disease*.

The CFR is often used to estimate the Infection Fatality Rate (IFR), which is the percentage of people infected with the disease that are expected to die. How close the CFR gets to the IFR depends on how well cases of the disease are identified and recorded. If every person who contracts the disease (both symptomatic and asymptomatic) and every death attributable to the disease is known and recorded, then the CFR will equal the IFR.

The biggest challenge in estimating the IFR is determining the denominator (all contractions of the disease). At the beginning of an outbreak , the CFR is likely to be much higher than the IFR due to milder cases not being reported or recorded (and perhaps not even known by the affected individual).