Is hepatitis B transmitted through sex?

Q: I heard that Hepatitis B is transmitted through sex? One of my friend is 27 years old and he was found to be Hepatitis B positive 5 years ago. Recently he got married and his wife is not vaccinated for Hepatitis B. Now she is carrying and in a recent test, she was found to be negative for HbsAg test. How is this possible?

A:The transmission of Hepatitis B through sex is not very efficient. Transmission through infected blood is more efficient and common.It is quite possible for the spouse of a hepatitis B positive patient to be seronegative. The factors affecting the transmission depend on the level of the virus in the blood the markers for which include viral load (through molecular methods like PCR / NASBA) and HBeAg.