**Core Concept**
Hepatitis E is a liver disease caused by the hepatitis E virus (HEV), which is transmitted through the fecal-oral route. The severity of HEV infection can vary depending on the age and underlying health status of the individual.

**Why the Correct Answer is Right**
In pregnant women, particularly those in the third trimester, HEV infection can lead to fulminant hepatic failure, which is characterized by rapid deterioration of liver function and can be fatal. This is due to the virus's ability to cause massive necrosis of liver cells and disrupt the normal functioning of the liver. The exact mechanism is not fully understood, but it is thought to be related to the virus's ability to infect and replicate in the liver cells of pregnant women.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because while HEV infection can cause severe disease in individuals with underlying health conditions, such as liver disease or immunosuppression, it is not the correct answer in the context of an epidemic of hepatitis E.
* **Option B:** This is incorrect because HEV infection is not typically associated with a high fatality rate in children. While children can become infected with HEV, they are generally asymptomatic or have mild symptoms.
* **Option C:** This is incorrect because HEV infection is not typically associated with a high fatality rate in individuals over the age of 50. While older adults may be more susceptible to severe disease, they are not the group with the highest fatality rate during an epidemic of hepatitis E.

**Clinical Pearl / High-Yield Fact**
In pregnant women, particularly those in the third trimester, HEV infection can lead to fulminant hepatic failure, which is a medical emergency that requires prompt recognition and treatment. It is essential for healthcare providers to be aware of this risk and take appropriate measures to prevent and manage HEV infection in pregnant women.

**Correct Answer:** D.