Epstein-Barr virus antibody in cases and contacts of infectious mononucleosis; a family study.

Serological investigations were carried out on 147 patients with Paul-Bunnell positive infectious mononucleosis (IM) from the general population. All possessed antibody to the Epstein-Barr virus (EBV) and 63% showed serological evidence of recent infection. Contacts of 132 patients, 306 in all, were followed serologically; within 6 months of the index cases' illness twenty one contacts developed evidence of EBV infection or re-infection and of these five developed overt IM. The secondary attack rate of EBV infection among susceptible contacts was at least 19%; the corresponding figure for clinically apparent IM was 6%. EBV antibody prevalence among patients' siblings was significantly lower than among age-matched controls, suggesting that cases of IM come from families with a lower than normal previous experience of the virus. Of thirteen patients with persistently Paul-Bunnell negative ;glandular fever' four had serological evidence of recent EBV infection and two had probable cytomegalovirus mononucleosis. Recent EBV infection may have been associated with the illnesses of five of the remaining patients.