Intrafamilial transmission of Epstein-Barr virus infections.

Intrafamilial transmission of Epstein-Barr virus infections was studied in 35 families. After infectious mononucleosis was diagnosed in an index child, all siblings were tested for antibodies to EBV. Susceptible children were retested in four to eight weeks. In five families, a concurrent seroconversion was detected in an asymptomatic younger child. Two of 35 seronegative siblings developed clinical IM, confirmed serologically, during the study period. Overall, there was evidence of spread in 7 (20%) of the 35 families. We conclude that there is significant intrafamilial transmission of IM. Our findings are compatible with an incubation period of four to six weeks.