Case fatality rate is defined as:

• A. The number of deaths caused by the disease among those with the disease, expressed as a percentage.
• B. The total number of deaths from all causes in the population in a given period.
• C. The number of deaths due to the disease divided by the total population, times 100.
• D. The number of new cases during a defined period divided by the population at risk.

Answer: (A)

Case fatality rate measures how deadly a disease is among those who actually have it. It is the number of deaths caused by the disease divided by the number of people diagnosed with the disease, multiplied by 100 to express it as a percentage. This focuses the measure on those who are ill, not on the whole population, which is why it’s expressed as a percentage of cases.

Think of it as theSeverity among cases: how likely it is for someone with the disease to die from it. That distinguishes it from other metrics. For example, using all deaths in the population would mix many different causes (not disease-specific), and dividing deaths by the total population would give a disease-specific mortality rate, not the fatality rate among those who have the disease. Counting new cases per population at risk reflects incidence or attack rate, not how deadly the disease is once it occurs.

Keep in mind that CFR can change with how well cases are detected, the time elapsed since cases began, and access to care, since these factors affect the number of deaths among identified cases.