If a prenatal patient tests positive for hepatitis B surface antigen (HBsAg), what immediate action should be taken for her infant at delivery?

When a prenatal patient tests positive for hepatitis B surface antigen (HBsAg), the immediate action for her infant at delivery is to administer both the hepatitis B vaccine and hepatitis B immune globulin (HBIG). This is critical because it provides the best protection against vertical transmission of hepatitis B from mother to child during childbirth.

By giving the infant the hepatitis B vaccine within 12 hours of birth, the vaccine helps the infant build immunity against the virus. Additionally, HBIG is a specially prepared immune serum that further decreases the risk of the infant contracting hepatitis B from the mother. This combination of vaccination and passive immunization with HBIG is recommended by the Centers for Disease Control and Prevention (CDC) and is crucial in preventing chronic hepatitis B infection in the child.

Monitoring the infant for signs of hepatitis B or prohibiting breastfeeding would not provide the necessary immediate preventive care, as the risk of transmission is addressed directly through vaccination and immune globulin. Blood transfusion is also unrelated to the immediate care required in this situation. Thus, administering both the vaccine and HBIG is the appropriate and evidence-based response to ensure the infant's health and well-being in the context of maternal hepatitis B.