In the studies on 21 HBsAg positive families in Iriomote Island, Nichinan and Fukuoka City, 99 HBsAg positive cases were tested for the presence of eAg and eAb.
eAg and eAb were detected in 35.4% and 20.0%, respectively. eAg was detected more frequently in young age group and its highest positive rate was observed in age of under 9. The frequency of eAb was highest in age of 10-19.
Two years follow up study on 14 cases revealed no changes in 10 cases with eAg or eAb and acquisition of eAg or eAg in 4 cases during the period of observation.
In 5 out of 6 families in which parents were negative for HBsAg and 2 or more children were positive, eAg was detected at least in one of children and positive rate reached to 66.7%. In contrast to these families, 7 families with single HBsAg positive case had no eAg positive case.
These results suggest that eAg is closely associated with infectivity of HB virus and suggest the possibility of horizontal transmission in intrafamilial spread.

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