Epstein-Barr virus infections in families: the role of children with infectious mononucleosis.

We performed a prospective evaluation of Epstein-Barr virus (EBV) infections in 78 families with a childhood index case of EBV-infectious mononucleosis (EBV-IM). During the acute index episode, adult family (household) contacts, compared with control adults, had a greater rate of oropharyngeal EBV excretion and high serum antibody responses, which suggested a recent antecedent reactivation of an old EBV infection. The increased prevalence of oropharyngeal EBV and acute serological responses found in sibling family contacts during the early surveillance period suggested that these contacts had experienced an increased rate of primary-type EBV infections shortly before or concurrent with the index case. Although nonimmune sibling contacts seroconverted at a slow rate, five of nine manifested IM with their eventual documented primary EBV infection. This study noted significant intrafamilial EBV activity surrounding an episode of childhood EBV-IM. Reactivation of an old EBV infection in adults may be an important source of virus for susceptible children within these families. Siblings of a childhood case of EBV-IM appear to be at increased risk for manifesting IM with their primary EBV infection.