**Core Concept:** Incidence rate is a measure of the number of new cases occurring within a defined population during a specified period. It is calculated as the number of new cases divided by the population size and multiplied by 1000 for easier interpretation.

**Why the Correct Answer is Right:** The correct answer is calculated as follows:

First, find the total number of new cases: 22 new cases.
Next, find the total population size during this period: 1,65,000.
Now, divide the total number of new cases by the population size: (22 / 1,65,000) * 1000 = 1.321 per 1000.

**Why Each Wrong Option is Incorrect:**

A. The calculation involves dividing the new cases by the population size, not adding them to the total cases.
B. The calculation involves dividing the number of new cases by the population size and multiplying it by 1000 for easier interpretation.
C. The calculation involves dividing the number of new cases by the population size and multiplying it by 1000 for easier interpretation. This is the correct answer.
D. The calculation involves multiplying the number of new cases by the number of days in the period and dividing by the population size, which is not the correct method.

**Incidence Rate (Core Concept)**: The incidence rate is a measure of the number of new cases occurring within a defined population during a specified period. It is calculated as the number of new cases divided by the population size and multiplied by 1000 for easier interpretation.

**Why Each Wrong Option is Incorrect**:

A. The calculation involves multiplying the number of new cases by the number of days in the period and dividing by the population size, which is not the correct method.
B. The calculation involves adding the number of new cases to the total cases, which is incorrect.
C. The calculation involves dividing the number of new cases by the population size and multiplying it by 1000 for easier interpretation. This is the correct answer.
D. The calculation involves multiplying the number of new cases by the number of days in the period and dividing by the population size, which is not the correct method.

**Clinical Pearls (Highlighting Key Points)**:

1. Incidence rates are expressed as a number of cases per 1,000 persons per year (or month, week, etc.) to make the number more meaningful and easier to interpret.
2. When calculating incidence rate, it is essential to use the correct method involving dividing the number of new cases by the population size and multiplying by 1000 for easier interpretation.
3. The calculation involves dividing the number of new cases by the population size and multiplying by 1000 for easier interpretation.
4. The correct method is to divide the number of new cases by the population size and multiply by 1000 for easier interpretation.