Occult hepatitis B virus infection in maintenance hemodialysis patients: prevalence and mutations in “a” determinant

Background：Occult hepatitis B virus infection (OBI) is rare and its diagnosis is often overlooked, but there is still a risk of HBV transmission. To analysis the prevalence of OBI among maintenance hemodialysis (MHD) patients in Sichuan Provincial People’s Hospital, the molecular biological characteristics of OBI and the mutation of “a” determinant were investigated. Method: A total of 330 patients undergoing hemodialysis at Sichuan Provincial People’s Hospital and its satellite dialysis units were tested for HBV markers by ELISA. HBV-DNA was detected by real-time PCR in patients with HBsAg negative/ HBcAb positive to investigate the prevalence of OBI. For plasma samples with persistent HBV DNA positive, the S gene was determined by nested PCR, and the sequence of gene mutation was compared with the standard sequence. Result: Among 330 patients, ages range from 27 to 95 with a mean of 60.66 years old and majority of patients (57.6%) > 60 years old. Serum from 165 of 180 HBsAg negative/HBcAb positive individuals were tested for HBV DNA by real-time PCR. 7 of 165 patients had low level of HBV DNA. Of those, 5 individuals were both HBcAb and HBsAb positive, and 2 individuals were HBcAb positive alone. After 2 years follow-up, 2 individuals with HBcAb positive alone were both tested HBV DNA again, but the other patients were not. Serum from the 2 patients were used nested PCR to confirm the genotype and the mutation of S gene. We found they both were genotype B. Amino acid sequencing confirmed that one had no mutations and the other one had Q128R, T131N, M133S, F134L and D144E mutants in “a” determinant. Conclusion: Chronic HBV infection was 7.3% (24/330) and OBI was 2.1% (7/330) in our hospital hemodialysis center. The genotype of patients with OBI were genotype B. Mutations of Q128R，T131N，M133S，F134L and D144E might be the potential sites associated with OBI.