**Core Concept**
Case fatality rate (CFR) is a measure of the severity of a disease, reflecting the proportion of individuals infected with a particular pathogen who die from the infection. It is calculated as the number of deaths due to a specific disease divided by the total number of cases of that disease, usually expressed as a percentage.

**Why the Correct Answer is Right**
The virulence of an organism refers to its ability to cause disease and death in an infected individual. Case fatality rate is a direct reflection of an organism's virulence, as it quantifies the proportion of infected individuals who succumb to the disease. A high CFR indicates a highly virulent organism, whereas a low CFR suggests a less virulent pathogen. The CFR is often used in epidemiology to assess the severity of a disease outbreak and to inform public health interventions.

**Why Each Wrong Option is Incorrect**
**Option A:** Communicability of infection refers to the ease with which a disease can be transmitted from one individual to another. While communicability is an important aspect of disease dynamics, it is not directly related to case fatality rate.

**Option B:** History of disease refers to the temporal distribution of a disease, including its incidence, prevalence, and duration. While understanding the history of a disease is crucial for public health planning, it is not directly related to case fatality rate.

**Option D:** Contribution of a disease among all deaths refers to the proportion of deaths attributed to a specific disease within a population. While this measure provides insight into the burden of a disease, it is distinct from case fatality rate, which specifically reflects the severity of a disease.

**Clinical Pearl / High-Yield Fact**
A high case fatality rate is often associated with highly virulent organisms, such as Vibrio cholerae or Yersinia pestis, which can cause severe and rapidly progressing disease. In contrast, a low CFR may indicate a less virulent pathogen, such as influenza or norovirus, which typically cause milder disease.

✓ Correct Answer: C. Virulence of organism