When does HBsAg peak during its infection course?

The correct answer is that HBsAg (Hepatitis B surface antigen) typically peaks during the first week of symptoms. This phase of infection is characterized by the body’s response to the Hepatitis B virus, leading to the onset of acute symptoms such as fatigue, jaundice, and abdominal pain.

During this initial week of symptoms, the viral replication is at its highest, resulting in increased levels of HBsAg in the bloodstream. This peak in HBsAg correlates with the onset of the immune response against the virus, which is important for diagnosis and monitoring of Hepatitis B infection.

While HBsAg does appear before symptoms manifest, its peak is more pronounced once those symptoms begin. After this initial peak, levels may fluctuate as the body starts to combat the virus. Following the resolution of symptoms, HBsAg levels typically decline as the infection resolves or transitions to a chronic state, hence making the timing of the peak critical for understanding the infection's course.