Blood screening for HBV DNA

Occult Hepatitis B virus infection in previously screened, blood donors in Ile-Ife, Nigeria: implications for blood transfusion and stem cell transplantation

BACKGROUND

Hepatitis B virus (HBV) transmission through blood transfusion is reduced by screening for hepatitis B surface antigen (HBsAg). However this method cannot detect the presence of occult hepatitis B virus infection. This study sought to determine the prevalence of occult hepatitis B virus infection among blood donors in Ile-Ife, Nigeria. For the first time in Nigeria we employed an automated real-time PCR- method to investigate the prevalence of occult HBV in blood donors.

METHODS

Blood donors screened with HBsAg immunochromatographic rapid test kits at the blood transfusion units of two hospitals and found to be negative were recruited into the study. Questionnaires to elicit risk factors for HBV infection were administered and then 10 ml of blood was collected from each donor. Plasma samples obtained from these HBsAg negative blood donors were screened again for HBsAg using an enzyme-linked immunosorbent assay (ELISA) method, and those found negative were screened for the presence of total antibody to the HBV core antigen (anti-HBc) using ELISA method. Those positive to anti-HBc were then tested for HBV DNA, using an automated real-time PCR method.

RESULTS

Five hundred and seven blood donors found HBsAg negative by immunochromatographic rapid test kits at both blood transfusion units, were tested for HBsAg using ELISA and 5 (1 %) were HBsAg positive. The 502 found negative were tested for anti-HBc and 354 (70.5 %) were found positive implying previous exposure to HBV and 19 (5.4 %) of the 354 anti-HBc positive had HBV DNA signifying occult HBV infection. No risk factors were found to be associated with the presence of HBV DNA among those who tested positive.

CONCLUSION

Occult HBV infection exists in blood donors in Ile-Ife, Nigeria and the use of HBsAg alone for screening prospective donors will not eliminate the risk of HBV transmission in blood transfusion or stem cell transplantation.

Molecular mechanisms underlying HBsAg negativity in occult HBV infection

Although genomic detection is considered the gold standard test on HBV infection identification, the HBsAg investigation is still the most frequent clinical laboratory request to diagnose HBV infection in activity. However, the non-detection of HBsAg in the bloodstream of chronic or acutely infected individuals has been a phenomenon often observed in clinical practice, despite the high sensitivity and specificity of screening assays standardized commercially and adopted in routine. The expansion of knowledge about the hepatitis B virus biology (replication/life cycle, genetic variability/mutability/heterogeneity), their biochemical and immunological properties (antigenicity and immunogenicity), in turn, has allowed to elucidate some mechanisms that may explain the occurrence of this phenomenon. Therefore, the negativity for HBsAg during the acute or chronic infection course may become a fragile or at least questionable result. This manuscript discusses some mechanisms that could explain the negativity for HBsAg in a serological profile of individuals with HBV infection in activity, or factors that could compromise its detection in the bloodstream during HBV infection.

Development of cost-effective real-time PCR test: to detect a wide range of HBV DNA concentrations in the western Amazon region of Brazil

Background

Currently there is a significant risk of infection with hepatitis B virus (HBV) during blood transfusion in high epidemic area. This is due to the pre-seroconversion window period, immunovariant viral strains and the presence of occult HBV infection (OBI). The aim of this study was to develop an in-house real-time PCR-based method, which was both ultra-sensitive and efficient offering an alternative method for nucleic acid testing (NAT).

Methods

A precore fragment with 109 bp was cloned and serial diluted to standard curve construction. The calibration of the HBV - DNA values was performed against OptiQuant® HBV-DNA Quantification Panel, Acrometrix Europe B.V.).

Results

From our in-house plasmid we prepared serial dilutions ranging from 2 × 10³ – 2 × 10⁹ copies/ml. The threshold was adjusted automatically during analysis and the data collected were analyzed by linear regression (r² = 0.99). The limit of detection for the assay with pHBVRO standards was 2000/ml in a total reaction volume of 30 μl. We found a strong correlation between the two methods (r² = 0.9965 and p < 0.0001). The regression line give us the following equation: Log 10 (IU/mL) = 0.9038Log 10 (copies/mL) − 1.0643, suggesting that 1 IU/mL = 15 copies/mL.

Conclusions

Therefore, we can affirm that the qHBVRO PCR can detect HBV DNA in individuals with hepatitis B at any stage of the disease showing high capacity for NAT screening in hepatitis b donors. This results of sensitivity could provide an advance for automation in blood banks and increasing safety of patients who receive blood transfusions.

Current incidence and residual risk of hepatitis B infection among blood donors in the United States

BACKGROUND

This study used two approaches to estimate the current incidence of hepatitis B virus (HBV) in a US donor population.

METHODS

HBV incidence was estimated through the hepatitis B surface antigen (HBsAg) yield approach and the seroconversion method. Residual risk was estimated by the incidence–window period model. HBsAg yield refers to an HBsAg confirmed-positive, antibody against hepatitis B core antigen (anti-HBc)–nonreactive donation, adjusted for false-positive neutralization results. The number of HBsAg-seroconverting repeat donors divided by total number of person-years of evaluation or the HBsAg yield rate divided by HBsAg yield window gave rise to incidence estimates.

RESULTS

The seroconversion and the yield approach, respectively, gave an incidence estimate of 3.41 or 3.43 per 105 person-years. Using a revised infectious window period of 38 or 30 days for current HBsAg assays, the current residual risk for HBV was respectively estimated for 2006 to 2008 at 1 in 282,000 or 1 in 357,000 donations from the seroconversion approach and 1 in 280,000 or 1 in 355,000 donations from the yield approach. With the same database and methods, this is a decrease from 1 in 86,000 to 1 in 110,000 observed in 1997 to 1999.

CONCLUSIONS

Current HBV incidence and residual risk are lower than earlier estimates, especially in the youngest donors, but remain higher in the absence of HBV nucleic acid test than those for human immunodeficiency virus or hepatitis C virus (HCV). In addition to the exclusion of HBsAg false-positive donors, the reduction could reflect shortened window periods and decreased incidence rates due to vaccination or other reasons.

A cost-benefit analysis of blood donor vaccination as an alternative to additional DNA testing for reducing transfusion transmission of hepatitis B virus

A survey-based, cost-benefit analysis was performed comparing blood screening strategies with vaccination strategies for the reduction of transfusion transmission of HBV. 231 whole blood donors and 126 apheresis donors were eligible and completed a questionnaire detailing their donation habits. The cost-benefit analysis included current mandatory HBV testing (HbsAg+anti-Hbc, A1), A1 with additional nucleic acid testing (NAT) for minipool (A2) or individual donation testing (A3), as well as HBV vaccination strategies using time-dependant (B1) or titre dependent booster vaccination solely (B2), or B2 in addition to current mandatory testing procedures (B3). Different cost models were applied using a 5% rate of discount. Absolute costs for current mandatory testing procedures (A1) over 20 years in Germany were €1009 million. Additional NAT would lead to incremental costs of 43% (A2) or 339% (A3), respectively. Vaccination strategies B1 and B2 showed cost-reductions relative to A1 of 30% and 14%, respectively. The number of remaining HBV infections could be reduced from 360 (for A1) to 13, using vaccination, compared with 144 or 105 remaining infections for A2 or A3, respectively. Absolute cost per prevented infection is similar (€2.0 million) for A2 and B3. HBV vaccination offers the near-elimination of transfusion infections while representing a potential cost-reduction.