Source of transmission in children with chronic hepatitis B infection after the implementation of a strategy for prevention in those at high risk

In order to clarify the sources of chronic HBV (hepatitis B virus) infection in children after the implementation of an "at-risk" strategy in Japan, chronically infected children were assessed. In addition, chronically infected children born to HBsAg-negative mothers and their family members were assessed to identify the sources of HBV transmission. Fifty-seven children who tested HBsAg-positive after the initiation of a mother-to-child transmission prevention program were enrolled in this study. The full-genome HBV DNA sequence was analyzed to confirm the transmission sources. Of the 57 patients, 37 (65%) were born to HBV carrier mothers. The remaining 20 (35%) patients were born to HBsAg-negative mothers. Fourteen of these patients had HBV carrier fathers, and 2 patients, who were siblings, did not have an HBV carrier father. The remaining 4 patients had no family members with HBV infection. Phylogenetic tree analysis confirmed that father-to-child transmission and sibling-to-sibling transmission occurred in 3 families and 1 family, respectively. Although vaccine failure of mother-to-child transmission was the major cause of chronic HBV infection in children, father-to-child transmission was the second most common mode of transmission. In addition, sibling-to-sibling transmission was found. Unless at-risk individuals and groups can be accurately identified to prevent horizontal transmission, the introduction of universal vaccination is essential for achieving the elimination of HBV infection in Japan.