Yes, over 99% of all adults over age 25 worldwide will test positive for Epstein-Barr virus (EBV). This does not mean they have EBV reactivation or any current effects from the virus. Most people have asymptomatic infections when they are first exposed to EBV, however, teens or young adults exposed to EBV often develop mononucleosis, also known as "mono" or glandular fever. It is important to note that prior exposure will make a person test positive for EBV VCA IgG antibodies, and in most cases EBNA (nuclear antigen) IgG antibodies, as well. These tests do not, however, indicate EBV reactivation, simply past exposure to EBV.