A patient in whom only hepatitis B virus (HBV) was thought to have been contracted, by kissing, from a same-sex partner coinfected with HBV and human immunodeficiency virus-1.

A 31-year-old homosexual man was admitted to our hospital in August 2001 with liver dysfunction. His diagnosis was acute hepatitis B. He had had a steady partner coinfected with hepatitis B virus (HBV) and human immunodeficiency virus-1 (HIV) from August 2000 to July 2001. Because he knew that the partner was infected with HIV, the sexual relationship had included only deep kissing, with no oral-genital or anal-genital sex. The serum HBV DNA level of the partner was relatively high compared with the serum HIV RNA level. Direct sequencing of the full HBV DNA genome from serum showed that the entire base sequences of the viruses from both patients were of genotype A and identical. HBV infectivity was shown to be stronger than that of HIV in our patient, in whom only HBV was transmitted from a partner coinfected with HBV and HIV. This case highlights the importance of HBV as a sexually transmitted disease.