Objective: This study aimed to examine the prevalence of antibodies against hepatitis A (anti-HAV) in a population of institutionalized mentally retarded persons compared with that of institutionalized non-mentally retarded persons in an area with moderate endemicity of HAV infection.

Methods: The study population was a group of mentally retarded persons aged between 10 and 30 years, institutionalized in one residence in Madrid, Spain. A group of non-mentally retarded subjects in the same age range was chosen as controls. Information about demography and duration of institutionalization was obtained by the investigator. Four drops of whole blood were obtained from each person by finger-stick, collected on filter paper, air-dried and stored at +4°C until antibody determination. Eluates were tested by an ELISA method.

Results: A total of 314 institutionalized subjects were included: 157 mentally retarded (mean age and mean duration of institutionalization were 24.4±3 and 9.7±5 years respectively) and 157 non-mentally retarded (mean age and mean duration of institutionalization were 19.2±5 and 4.6±3 years respectively). The prevalence of anti-HAV antibody was 54% (95% confidence intortal (CI) 50–58) in mentally retarded and 22% (95% CI 19–25) in non-mentally retarded [P<0.001; odds ratio (OR): 4.2 (95% CI 2.5–7)]. In both groups, these differences were not statistically significant for anti-HAV antibody prevalence between persons institutionalized for > 5 years compared with those institutionalized for ≤ 5 years.

Conclusions: There results indicate that in an area of moderate endemicity the institutionalized mentally retarded are at increased risk of having acquired hepatitis A infection compared to the non-mentally retarded. In these institutionalized persons, regardless whether they are mentally retarded or not, prevalence is not influenced by age or length of stay in institutions.