[Mentally deficient patients and infection caused by hepatitis B virus. Prevalence in our area].

To assess the prevalence of hepatitis B virus (HBV) infection in medium level mentally impaired patients (MIP), 620 MIP were evaluated; 181 of them had Down's syndrome and were active inmated of open institutions. At the time of the study, 28.7% had some positive serum marker of HBV infection, and 5.8% were virus carriers. The highest rate of seropositive individuals (48%) was found in male MIP with Down's syndrome. The rate of seropositive individuals was higher among those MIP who had attended special education centers than in those who had not. The tendency to remain as HBV carrier was higher in males with Down's syndrome. Our results confirm the need for prophylaxis in this population.