**Core Concept**
The underlying principle being tested is the effectiveness of pre-transfusion testing in preventing transfusion-transmitted infections, specifically hepatitis. Pre-transfusion testing includes screening for various markers of infectious diseases. However, the window period and limitations of screening tests can affect their efficacy.

**Why the Correct Answer is Right**
Pre-transfusion testing may not decrease the incidence of hepatitis due to the window period of the infection, during which the virus is not yet detectable by standard screening tests. This means that even if blood is screened, it may still contain hepatitis viruses that are not yet detectable.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not provided.
**Option B:** This option is incorrect because it is not provided.
**Option C:** This option is incorrect because it is not provided.
**Option D:** This option is incorrect because it is not provided.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that while pre-transfusion testing significantly reduces the risk of transfusion-transmitted infections, it is not 100% effective due to limitations such as the window period of infections and the potential for new or emerging pathogens.

**Correct Answer:** D. Window period of the infection and limitations of screening tests.