Prevalence of hepatitis B infection among residents of an institution for the mentally retarded.

Data on prevalence of antibody to hepatitis B surface antigen (anti-HBs) and of hepatitis B surface antigen (HBsAg) among 95 matched pairs of Down's syndrome (DS) and other mentally retarded (OMR) patients in an institution were analyzed by age on admission and by length of residence. Passive hemagglutination test were used to determine anti-HBs. Anti-HBs prevalence increased with admission age among DS patients (26%, 42% and 56% for age groups less than or equal to 5, 6-15 and greater than 15 years, respectively) but decreased among OMR patients (85%, 71% and 78%), giving overall rates of 38% for DS and 77% for OMR which are significantly different (p less than .001). Anti-HBs prevalence increased with length of residence for OMR patients but was unchanged for DS patients. For both groups, the prevalence of hepatitis B (HB) infection (both anti-HBs and HBsAg) increased with length of residence and, overall, was nearly the same for DS and OMR patients. These observations are consistent with the hypothesis that, with respect to response to HB virus, younger DS patients are immunologically immature.