A 2-month-old girl is brought to the clinic due to perinatal hepatitis B exposure. Her mother is age 22 and immigrated to the United States shortly after giving birth. The pregnancy was complicated by maternal hepatitis B infection. However, the mother received no prenatal or perinatal care and was not diagnosed with chronic hepatitis B until the immigration process. Maternal HBsAg, HBeAg, and anti-HBc are all positive; anti-HBs is negative. The infant has not been evaluated previously and has not received any immunizations or other medications. She is exclusively breast fed and has been growing normally. Vital signs are normal and physical examination is unremarkable. No hepatomegaly or jaundice is seen. The infant's laboratory results will most likely show which of the following?
Perinatal hepatitis B infection | |
Risk factors |
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Clinical findings |
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Prevention |
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This infant was exposed to hepatitis B virus (HBV) during delivery. Mother-to-child transmission most commonly occurs during delivery, but transplacental infection can also occur. Maternal viral load and HBeAg status are the strongest risk factors for infant infection. Infants born to HBeAg-positive women (as in this case) have a >90% chance of acquiring infection, whereas the chance is less in infants born to HBeAg-negative women.
Viral replication occurs rapidly in infected infants due to immune system immaturity in newborns. As a result, infected infants have high viral loads and HBeAg levels. Despite this high level of replication, infants enter an immune-tolerant phase of chronic HBV infection in which they are asymptomatic and have normal or only mildly elevated liver function tests. Over time, chronically infected newborns are at high risk of progression to cirrhosis and hepatocellular carcinoma. The chance of progression to chronic hepatitis B is 90% without treatment, much higher than the chance of progression in older children and adults. Administration of hepatitis B vaccine and immunoglobulin as soon as possible after delivery can prevent chronic infection.
(Choice A) Due to their immature immune system, more than 90% of vertically infected infants develop chronic infection (eg, they do not develop anti-HBs and do not clear their HBV infection). Additionally, the infant's mother has chronic disease and lacks anti-HBs, meaning there would be no maternally derived transplacental antibodies. Therefore, anti-HBs would not be expected in this infant.
(Choices C and D) Hepatic injury from hepatitis B is due to the cellular immune response, not by the virus itself. Therefore, infants with HBV infection enter an immune-tolerant phase due to their immature T-cell responses, which limits hepatocyte damage. As a result, laboratory markers of liver injury (eg, liver function tests, direct bilirubinemia) are usually normal or only mildly elevated in HBV-infected neonates.
(Choice E) Perinatally infected infants have rapid appearance of HBsAg within a few days; absence of both HBsAg and anti-HBs at age 2 months would suggest that the infant was not infected. However, this is unlikely as virtually all infants born to HBeAg-positive mothers will be infected perinatally.
Educational objective:
Infants born to HBeAg-positive mothers have a high risk of acquiring perinatal hepatitis B virus (HBV) infection. Infected neonates have high levels of HBV replication and are at high risk for chronic infection, but are usually asymptomatic or have only mildly elevated liver function tests.