In epidemiology, a case fatality rate (CFR) — or case fatality risk, case fatality ratio or just fatality rate — is the proportion of deaths within a designated population of "cases" (people with a medical condition), over the course of the disease. A CFR is conventionally expressed as a percentage and represents a measure of risk. CFRs are most often used for diseases with discrete, limited time courses, such as outbreaks of acute infections.