Risk of hepatitis B in infancy and childhood.

Hepatitis B virus (HBV) may be transmitted from mother to child during delivery or in the neonatal period (vertical transmission) or by direct person to person contact in teenagers and adults (horizontal transmission). Patients infected horizontally, as occurs in countries with a low prevalence of infection, achieve complete resolution in up to 95% of cases and acquire permanent immunity. On the other hand, 95% of infected newborns cannot clear the virus and remain chronic carriers. The relevance of this method of infection in newborns is twofold. First, because of persistent infection throughout life, they are at risk of developing liver cirrhosis and hepatocellular carcinoma. Second, they are permanent reservoirs of hepatitis B infection, facilitating its spread. Even in countries with low or intermediate prevalence, the importance of vertical transmission is manifest. In a study carried out in our hospital before screening of pregnant women for hepatitis B surface antigen (HBsAg) was implemented, the prevalence of HBsAg carriers among 8200 pregnant women was 1.24%, 6% of whom were HBeAg positive, for a minimum rate of transmission of HBV of 6%. From these data, there will be at least 65 children per year in Catalonia who become chronic carriers and about 1000 children at risk of acquiring HBV infection. Epidemiological studies carried out in Catalonia confirmed our results. Among children under 10 years of age in whom vertical transmission was likely, 1.7% had serum markers of HBV infection and 0.2% were HBsAg positive. These data confirm the need for universal HBV prevention in newborns, in addition to any other programme carried out in teenagers or adults.