Most patients with infectious mononucleosis are caused by EBV infection, which continues to excrete the virus in the mouth after infection. Infectious mononucleosis can therefore be transmitted through oral contact through intimate acts such as kissing.
However, most people with EBV infection are asymptomatic, with no signs or symptoms, and almost all adults over the age of 35 have antibodies to EBV, suggesting previous infection. About one quarter of adolescents can develop infectious mononucleosis following EBV infection, which presents with fever, sore throat and swollen lymph nodes.