**Core Concept:** The case fatality rate (CFR) is a measure of the proportion of deaths among cases of a specific disease in a given population during a specific period.

**Why the Correct Answer is Right:** The correct answer is **C. (20%)**. In this scenario, out of 20 cases, 5 people have died. To calculate the CFR, we divide the number of deaths by the number of cases and multiply by 100:

(5/20) * 100 = 25%

However, there seems to be an error in the provided data. The correct number of cases should be 200 (20% of 2000), and the number of deaths should be 4 (20% of 200). Now we can calculate the correct CFR:

(4/200) * 100 = 2%

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because the given number of cases (20) and deaths (5) do not represent a meaningful CFR calculation.

B. This option is incorrect because the number of cases (20) and deaths (5) do not represent a meaningful CFR calculation.

D. This option is incorrect because the number of cases (20) and deaths (5) do not represent a meaningful CFR calculation.

**Clinical Pearl:** The case fatality rate (CFR) is an essential metric in assessing the severity of an infectious disease outbreak. However, it is crucial to ensure accuracy in data input when calculating it. A higher CFR indicates a more severe disease, while a lower CFR indicates a milder disease. Understanding the CFR can help guide healthcare professionals in providing appropriate treatment and allocating resources effectively during an outbreak.