Family incidence of type B hepatitis.

Family incidence of HBsAg-positive viral hepatitis was confirmed to be high. In 499 families with a type B viral hepatitis patient, type B viral hepatitis morbidity among 1116 contacts amounted to 2.24% within 6 months of the primary patients' hospitalization (being 188.2 times higher than semiannual morbidity of the population of the Czech Socialist Republic, CSR) and the prevalence of HBsAg amounted to 8.96% (being 22.4 times higher than among the population of CSR). On deducting positive findings at first blood samplings, which at least partially eliminated individuals who could themselves have been the source of infection for the first patient in each family, the rate for contact cases equalled 0.70% (58.8 times higher morbidity than among the population) and the rate for HBsAg prevalence equalled 2.50% (6.25 times higher than among the population). Among 917 members of 335 families where a case of HBsAg-negative viral hepatitis occured, 0.32% developed HBsAg-positive viral hepatitis within 6 months (26.8 times higher morbidity than population morbidity) and the HBsAg prevalence was 2.94% (7.35 greater than among the population). On deducting the first positive findings no clinical illness remained and HBsAg prevalence equalle 0.98% (2.45 times higher than among the population). The highest HBsAg prevalence was found among contacts aged 0-5 years (17.09% for the whole period, 3.41% after deducting first positive findings) and 40 years and over (10.82% and 3.39%, respectively). Type B viral hepatitis morbidity was again highest in the age groups of 0-5 years (5.12%) and 40 years and over (2.54%) for the whole period. On deducting first positive findings, the 40+ years group displayed the highest morbidity (1.27%), whereas the 0-5 years group displayed zero morbidity. Disclosure of the mechanisms of nonparenteral or inapparently parenteral transmission specific for family environments would be important for the prospect of introducing adequate measures to limit or prevent the spread of type B viral hepatitis.