http://en.wikipedia.org/wiki/Hepatitis_BHBV can be transmitted between family members within households, possibly by contact of nonintact skin or mucous membrane with secretions or saliva containing HBV.
However, at least 30% of reported hepatitis B among adults cannot be associated with an identifiable risk factor.这是不是也解释了新到上的为什么中国乙肝比AIDS更多？另外，据说黄种人更容易感染HBV