Background: Isolated antibody to hepatitis B core antigen (anti-HBc) is frequently found in HIV-infected patients. The present study aimed to determine the prevalence and risk factors of isolated anti-HBc and the anamnestic response to hepatitis B vaccination in this population.

Material and Method: HIV-infected patients who visited Ramathibodi Hospital in May 2006 were included to test hepatitis B serology. Subjects with isolated anti-HBc were given hepatitis B vaccine and tested for anti- HBs.

Results: Of 140 patients, 28 (20%) had isolated anti-HBc. From multivariate analysis, IVDU (OR 30.8, p<0.001) and anti-HCV seropositive (OR 6.7, p = 0.002) were independent risk factors for isolated anti-HBc. Two from 28 (7%) patients who received vaccine had a response to vaccination.

Conclusion: Prevalence of isolated anti-HBc among Thai HIV-infected patients was 20%. Risk factors of isolated anti-HBc were IVDU and anti-HCV seropositive. Anamnestic response to hepatitis B vaccination was low. Further study with strategies to improve the response of vaccination is needed.

Keywords: Anti-HBc, HBV, Hepatitis B, HIV, Vaccination