**Core Concept**
Nosocomial infections, also known as hospital-acquired infections (HAIs), are infections that patients acquire during their hospital stay. These infections are a significant concern in healthcare settings, as they can lead to prolonged hospital stays, increased morbidity, and mortality.

**Why the Correct Answer is Right**
The Centers for Disease Control and Prevention (CDC) defines a nosocomial infection as one that occurs 48 hours or more after hospital admission. This timeframe is used to differentiate between infections acquired before hospital admission (community-acquired) and those acquired during the hospital stay. The 48-hour window is not a hard and fast rule, but it provides a general guideline for clinicians to identify potential nosocomial infections.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too short a timeframe to determine a nosocomial infection. A patient may still be in the early stages of an infection acquired before hospital admission.
**Option B:** This option is incorrect because it is too broad and does not provide a specific timeframe.
**Option C:** This option is incorrect because it is too long a timeframe and may include infections acquired after hospital discharge.

**Clinical Pearl / High-Yield Fact**
It is essential for healthcare providers to accurately identify nosocomial infections to implement infection control measures and prevent the spread of pathogens within the hospital environment.

**Correct Answer: C. 72 hours. Nosocomial infections are typically defined as those occurring 72 hours or more after hospital admission.