The epidemiology of hepatitis B in a residential institution for the mentally retarded.

A longitudinal study carried out over 43 months in a residential home for the mentally retarded confirmed the marked propensity of individuals with Down's syndrome (DS) to develop chronic HB antigenaemia. This could not be accounted for by environmental factors, and a genetic basis is postulated. In addition, DS subjects appeared innately more susceptible to hepatitis B virus (HBV) infection, requiring one-third the patient-months of exposure of non-Down's subjects (ND) before showing evidence of infection. The reciprocal geometric mean titre of anti-HBS in DS subjects was 110 compared with 705 in ND subjects, suggesting a deficiency of humoral immunity in the DS subjects. Transmission of HBV was occurring by means other than therapeutic, prophylactic, dental or diagnostic procedures, in the institution, and possible modes of transmission are discussed. These were probably both parenteral and non-parenteral. Eighty-one per cent of HBV infections in the Home were subclinical.