. A useful index to measure the lethality of an acute infectious diseases is-
**Core Concept**
The lethality of an acute infectious disease is a measure of the severity of the disease and its potential to cause death. This concept is crucial in epidemiology and public health to assess the impact of a disease on a population.
**Why the Correct Answer is Right**
The correct answer is the case-fatality ratio (CFR), which is the proportion of individuals with a particular disease who die from that disease. CFR is a useful index to measure the lethality of an infectious disease because it takes into account the number of cases and deaths due to the disease. It is calculated by dividing the number of deaths due to the disease by the total number of cases. CFR is an important indicator of the severity of a disease and is used to evaluate the effectiveness of public health interventions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it refers to the basic reproductive number (R0), which is a measure of the average number of secondary cases generated by a single infected individual in a completely susceptible population. While R0 is an important indicator of the transmissibility of a disease, it does not directly measure lethality.
**Option B:** This option is incorrect because it refers to the attack rate, which is the proportion of individuals in a population who become infected with a disease after contact with an infected individual. Attack rate is a measure of the contagiousness of a disease, but not its lethality.
**Option C:** This option is incorrect because it refers to the mortality rate, which is the proportion of deaths due to a disease in a population over a specific time period. While mortality rate is related to lethality, it does not take into account the number of cases, making it a less accurate measure of disease severity.
**Clinical Pearl / High-Yield Fact**
CFR is an important indicator of the severity of a disease, and it is often used in conjunction with other epidemiological measures, such as the basic reproductive number (R0) and attack rate, to assess the impact of a disease on a population.
**Correct Answer: C. Mortality rate.