Antibody to hepatitis A antigen in institutionalized mentally retarded patients.

Institutionalized patients with Down syndrome and matched controls with other causes of mental retardation were tested by immune adherence hemagglutination for the presence of antibody to hepatitis A antigen (anti-HA). Altogether 75.1% (175 of 233) exhibited presence of anti-HA, with no differences by sex or age. Patients reactive for hepatitis B surface antigen (HBsAg) or its antibody (anti-HBs) were reactive for anti-HA significantly more frequently than those with a negative reaction for these markers. In contrast to serologic markers of hepatitis type B, prevalence of anti-HA does not depend on the cause of mental retardation or on the age at primary infection. The rate of anti-HA positivity was found to be closely correlated with duration of institutionalization. The study confirmed that many closed institutions for the mentally retarded are hyperendemic for hepatitis type A and that formation of anti-HA is not greatly affected by either immune deficiency or immune immaturity.