Hepatitis B virus infection among mentally retarded patients in institutions, Okinawa, Japan.
To determine whether transmission of hepatitis B virus occurs among mentally retarded patients in six institutions, from 1986 to 1988, 373 patients (males 203, females 170, 18-53 years of age, mean age 29.9) were tested for hepatitis B markers. Seventy five of them had Down's syndrome. Overall prevalences were 9.1% for hepatitis B surface antigen (HBsAg), 39.7% for antibody to HBsAg (anti-HBs) and 48.0% for antibody to hepatitis B core antigen (anti-HBc). Prevalence of HBsAg was significantly higher in patients with Down's syndrome than in other mentally retarded patients. Five patients (three males and two females) in four institutions were infected with hepatitis B virus during the two years of observation. Four of these five patients were the other mentally retarded and became both anti-HBs and anti-HBc positive. The remaining one, who was 29 years old and Down's syndrome, became an HBsAg carrier. These observations indicate that hepatitis B virus transmission frequently occurs among mentally retarded patients in institutions and therefore vaccination of susceptible institutionalized patients is necessary. Vaccination to patients with Down's syndrome is particularly warranted, because they are uniquely predisposed to develop chronic hepatitis B infection following exposure.