**Core Concept**
The presence of HBeAg (Hepatitis B e-antigen) in patients with hepatitis B indicates the replication of the virus and the potential for viral transmission. HBeAg is a marker of active viral replication and is associated with a higher viral load.

**Why the Correct Answer is Right**
The presence of HBeAg is a marker of high infectivity in hepatitis B patients. This is because HBeAg is a protein produced by the virus during active replication. When HBeAg is present, it indicates that the virus is actively replicating and that the patient is more likely to transmit the virus to others. The high viral load associated with HBeAg positivity increases the risk of transmission through bodily fluids, such as blood and saliva.

**Why Each Wrong Option is Incorrect**
**Option A:** Simple carriers are typically HBeAg-negative and have a lower viral load, making them less infectious.
**Option B:** Late convalescence refers to the recovery phase of the disease, during which HBeAg would typically be undetectable.
**Option D:** Carrier status is a broader term that refers to anyone who is infected with the virus, regardless of their HBeAg status.

**Clinical Pearl / High-Yield Fact**
It's essential to note that HBeAg seroconversion (loss of HBeAg and development of anti-HBe) is a significant milestone in the natural history of hepatitis B, indicating a decrease in viral replication and infectivity.

**✓ Correct Answer: C. High infectivity**