Hepatitis B virus (HBV) DNA screening of blood donations in minipools with the COBAS AmpliScreen HBV test

Transfusion-transmitted hepatitis B virus infection

Hepatitis B virus (HBV) remains a major risk of transfusion-transmitted infection due to the pre-seroconversion window period (WP), infection with immunovariant viruses, and with occult carriage of HBV infection (OBI). Reduction of HBV residual risk depends upon developing more sensitive HBV surface antigen (HBsAg) tests, adopting anti-HBc screening when appropriate, and implementing HBV nucleic acid testing (NAT), either in minipools or more efficiently in individual samples. HBV NAT combines the ability to significantly reduce the window period and to detect occult HBV carriage substantiating decades of clinical observation that HBsAg-negative/anti-HBc-positive blood could transmit HBV. Clinical observations suggest limited transmission rate of occult HBV compared to WP. Low transmission rate might be related to low viral load observed in OBIs or to the presence of mutants associated with occult carriage. OBIs carrying detectable anti-HBs ( approximately 50%) are essentially not infectious by transfusion. However, recent data suggest that the neutralizing capacity of low anti-HBs may be inefficient when overcome by exposure to high viral load. Anti-HBc blood units without detectable anti-HBs appear moderately infectious except in immunocompromised recipients. Immunodeficient elderly and patients receiving immunosuppressive treatments may be susceptible to infection with lower infectious dose even in the presence of anti-HBs. The immune status of blood recipients should be taken into consideration when investigating "post-transfusion" HBV infection. Pre-transfusion testing and post-transfusion long-term follow-up of recipients, and molecular analysis of the virus infecting both donor and recipient are critical to definitively incriminate transfusion in the transmission of HBV.

Efficacy of hepatitis B virus (HBV) DNA screening and characterization of acute and occult HBV infections among blood donors from Madrid, Spain

BACKGROUND

Screening of blood units for hepatitis B virus (HBV) DNA identifies donations collected during the window period (WP) of the acute infection and may improve viral safety of the blood supply. It also leads to the detection of occult hepatitis B infection (OBI).

STUDY DESIGN AND METHODS

From January 2005 to December 2006, a total of 383,267 blood units were screened for hepatitis B surface antigen (HBsAg) and HBV DNA in two transfusion centers in Madrid, using either individual-donation nucleic acid testing (ID-NAT) or minipool (MP-NAT) of eight donations (MP8). Samples positive for HBV DNA and negative for HBsAg were confirmed by a second molecular test, the viral DNA was quantified, and a genome fragment including the region encoding the major hydrophilic region (MHR) of HBsAg was sequenced.

RESULTS

The overall yield of HBV DNA-positive, HBsAg-negative units was 1 in 21,282 (18 cases), higher when using ID-NAT than MP8-NAT (1:9862 vs. 1:51,011; p < 0.01). Four donations (1/95,817) were collected during the infectious pre-HBsAg WP, one during an early recovery stage, and the remaining 13 (1/29,482) were OBIs, six of whom had no detectable antibody to HBsAg. Low-level Genotype D HBV DNA was detected in all OBI cases; the frequencies of this genotype and MHR amino acid substitutions were significantly higher than reported from unselected Spanish HBsAg carriers. Donors with OBI had normal aminotransferase levels and were significantly older than donors carrying HBsAg.

CONCLUSIONS

Blood donors in the WP and with OBI are not uncommon in Madrid and are detected at a higher frequency with ID-NAT than MP-NAT.

First transmission of human immunodeficiency virus Type 1 by a cellular blood product after mandatory nucleic acid screening in Germany

BACKGROUND

In February 2007, a 63-year-old man underwent surgery. Retrospective testing with nucleic acid testing (NAT) showed that the patient was human immunodeficiency virus Type 1 (HIV-1) positive 10 days after transfusion. The transfusion-transmitted infection had been identified by a donor-related lookback started in April 2007 after anti-HIV seroconversion.

METHODS

Sequence analysis was performed in the gag-pol region as well as in the V3 loop env region. Archived plasma from the transmitting donation was investigated for the individual-donation NAT with the Roche COBAS AmpliPrep/COBAS TaqMan HIV-1 test (Roche CAP/CTM HIV-1 test) and for HIV antigen/antibody combination testing (Abbott Architect). Additional testing was done on the donor's follow-up sample and on the recipient's sample.

RESULTS

The Roche CAP/CTM HIV-1 test failed to detect viral RNA by minipool NAT in the index donation (April 2007) as well as in the donation that caused the infection (January 2007). Phylogenetic analysis showed a very high genetic similarity among viral sequences from both donor and recipient, proving the HIV-1 transmission by sequence data.

CONCLUSION

This case represents the first documented HIV-1 transmission by transfusion of red blood cells after mandatory introduction of HIV-1 NAT for blood screening in Germany. Low viral load and mismatches in the primer/probe region might explain the detection failure of the NAT screening assay. A certain risk remains that new virus variants contain mutations at positions critical for amplification or detection of viral genomes. An option to reduce the risk of a detection failure by NAT is the simultaneous use of several conserved regions as amplification targets.

Molecular characterization of occult hepatitis B cases in Greek blood donors

The use of sensitive nucleic acid testing for hepatitis B virus in blood donors revealed a number of HBV DNA(+) cases among HBsAg(-) donors, a status known as occult HBV infection. The purpose of this study was the serological and molecular characterization of occult HBV infection in Greek blood donors. A prospective study was undertaken in order to identify occult HBV infection cases in blood donors. As part of the routine screening of blood donations in Greece, blood units were screened individually by a multiplex HIV-1/HCV/HBV nucleic acid assay. Initially reactive samples were retested with discriminatory assays. HBV DNA(+)/HBsAg(-) samples were tested further for HBV serological markers and HBV DNA was quantified by real-time PCR. Molecular characterization was performed by sequencing the envelope and polymerase genes of HBV. Preliminary screening revealed 21 occult cases with the following patterns: anti-HBc only: 7 donors, anti-HBc/anti-HBs: 7 donors, anti-HBc/anti-HBe: 5 donors, anti-HBc/anti-HBs/anti-HBe: 2 donors. In all cases, the HBV DNA load was <351 IU/ml. Sequencing was successful in 10 donors (classified within genotype D) revealing several amino acid substitutions related to diagnostic escape and antiviral resistance. HBsAg diagnostic failure and low viral replication in occult HBV infection carriers could possibly be attributed to multiple changes in envelope and polymerase regions, respectively.

Risk assessment and cost-effectiveness/utility analysis

Decision-makers at all levels of public health and transfusion medicine have always assessed the risks and benefits of their decisions. Decisions are usually guided by immediately available information and a significant amount of experience and judgment. For decisions concerning familiar situations and common problems, judgment and experience may work quite well, but this type of decision process can lack clarity and accountability. Public health challenges are changing as emerging diseases and expensive technologies complicate the decision-makers' task, confronting the decision-maker with new problems that include multiple potential solutions. Decisions regarding policies and adoption of technologies are particularly complex in transfusion medicine due to the scope of the field, implications for public health, and legal, regulatory and public expectations regarding blood safety. To assist decision-makers, quantitative risk assessment and cost-effectiveness analysis are now being more widely applied. This set of articles will introduce risk assessment and cost-effectiveness methodologies and discuss recent applications of these methods in transfusion medicine.

Seroepidemiologic study of hepatitis B virus, hepatitis C virus, human immunodeficiency virus and syphilis infections in Iranian blood donors

To determine the frequency of hepatitis B, hepatitis C, Human Immunodeficiency Virus (HIV) and syphilis infections in Iranian blood donors. The prevalence of serological markers of hepatitis B, hepatitis C, HIV and syphilis infections were evaluated in 318029 consecutive volunteer blood donors attending to Tehran blood transfusion service from March 2005 to March 2006. Those positive for hepatitis B surface antigen, anti-HCV, anti-HIV1/2 and VDRL (venereal disease research laboratory) reactivity were analyzed with a second independent HBsAg enzyme immunoassay (EIA) and neutralization assay; an additional independent anti-HCV EIA and HCV-RIBA assay; second independent anti-HIV1/2 test, HIV western blot and fluorescent Treponemal Antibody Absorbed (FTA-ABS), respectively. In 318029 participants, prevalence of positive HBsAg, HCV RNA, HIV western blot and FTA-ABS was 1684 (0.487%), 323 (0.093%), 11 (0.003%) and 19 (0.005%), respectively. In 1014 subjects randomly selected from these 318029 participants, besides standard interview, physical exam and routine serologic tests; anthropometric and biochemical were studies. In this selected group frequency of HBsAg was 3 (0.29, 95% CI: 0-0.64%); frequency of anti-HCV was 21 (2.07%), but it was (0.09%, 95% CI: 0-0.30%) by confirmatory HCV RNA test; frequency of HIV-Abl, 2 was 8 (0.78%), but it was 2 (0.19%, 95% CI: 0-0.48%) by confirmatory test; frequency of RPR was 0 (0%, 95% CI: 0-0.30%). Despite excluding subjects with high-risk behaviors by standard interview and physical examination, still a few asymptomatic hepatitis B, hepatitis C, HIV-infected subjects existed among volunteer blood donors with demographic and biochemical findings similar to non-infected ones.

A new method of concentrating hepatitis B virus (HBV) DNA and HBV surface antigen: an application of the method to the detection of occult HBV infection

BACKGROUND

The risk of post-transfusion hepatitis B virus (HBV) infection has been reduced after the implementation of HBV nucleic acid amplification technology (NAT). However, the problem of HBV DNA-positive and HBV surface antigen (HBsAg)-negative occult HBV infections remains to be solved. This is in part due to the HBV DNA load being too low to detect these occult HBV infections using mini-pool NAT. In Japan, the assay for the antibody against the HBV core antigen (anti-HBc) has not completely excluded occult HBV infection. To solve this problem, we have developed a new method of concentrating HBV DNA and HBsAg simultaneously to increase the sensitivity of detection tests.

METHODS

Virus concentration is achieved by the enhancement of the agglutination of viruses using poly-L-lysine in the presence of a bivalent metal. Poly-L-lysine-coated magnetic beads are used to shorten the time of each step of the concentration procedure. Seventy-seven anti-HBc-positive and HBsAg-negative donations were examined. HBsAg and anti-HBc were tested by enzyme immunoassay (EIA) (AxSYM; Abbott) and haemagglutination inhibition test (Japanese Red Cross), respectively.

RESULTS

HBV surface antigen and HBV DNA levels were concentrated up to four- to sevenfold. Using this method, 35 of the 77 anti-HBc-positive and HBsAg-negative donors were HBV DNA-positive by individual NAT and a further five donors became HBV DNA-positive by HBV concentration. Twenty-seven of 40 occult HBV infections became HBsAg-positive by HBsAg concentration.

CONCLUSION

Our new method of concentrating HBV and HBsAg increased the sensitivities of EIA and HBV NAT, and enabled us to detect 27 of 40 occult HBV infections by HBsAg EIA.

Performance of an algorithm for the reentry of volunteer blood donors deferred due to false-positive test results for antibody to hepatitis B core antigen

BACKGROUND

Blood donor testing for antibody to hepatitis B core antigen (anti-HBc) has been used in the United States for more than 20 years as a surrogate to prevent transmission by transfusion of non-A, non-B hepatitis, as a human immunodeficiency virus surrogate, and to reduce transmission of hepatitis B virus (HBV). Nonspecific anti-HBc assays have caused deferral of hundreds of thousands of otherwise qualified donors. A more specific anti-HBc test and a sensitive HBV DNA test should permit donor reentry after false-positive anti-HBc.

STUDY DESIGN AND METHODS

A total of 1324 otherwise eligible volunteer donors, deferred for anti-HBc reactivity on more than one occasion, were recruited from four collection facilities. They were tested using a licensed, more specific anti-HBc test, a licensed hepatitis B surface antigen (HBsAg) test, and a licensed HBV DNA assay with a 95 percent limit of detection of not more than 10 copies per mL.

RESULTS

From 11 to 32 percent of donors contacted by participating sites entered the study. Overall, 488 (37%) of the donors were negative on the more specific anti-HBc test. The proportion of putative false-positive samples varied according to the test responsible for the original deferral. A single donor, negative for the presence of anti-HBc and HBsAg, was positive for the presence of HBV DNA in one of three replicates. Repeat testing of this donor 10 months later was negative for the presence of all markers of HBV infection, and the donor had a history of HBV vaccination with documented postimmunization anti-HBs seroconversion 10 years before her anti-HBc deferral, and was considered HBV DNA false positive.

CONCLUSION

These data support reentry of donors with false-positive anti-HBc results on the relatively nonspecific assays that have been in use in the United States for more than 20 years.

PRISM hepatitis B surface antigen detection of hepatits B virus minipool nucleic acid testing yield samples

BACKGROUND

Hepatitis B virus (HBV) residual risk has been estimated at 1:63,000-1:205,000 and introduction of more sensitive serological tests and nucleic acid testing (NAT) would reduce that risk. Sensitivity of the recently licensed Abbott PRISM hepatitis B surface antigen (HBsAg) CLIA and minipool (MP) HBV NAT has been described as comparable and thus the need for HBV NAT has not been compelling. In this study, eight samples identified as yield samples with MP HBV NAT were tested using the PRISM test.

STUDY DESIGN AND METHODS

Seven samples were identified using the Roche COBAS AmpliScreen HBV test and one additional sample was obtained from the clinical trial for the Roche cobas TaqScreen MPX test. Each of these samples was reactive by MP HBV NAT and nonreactive for HBsAg using one of three licensed enzyme immunoassay (EIA) tests. After licensure of the PRISM HBsAg, aliquots were tested with this assay, and DNA quantitation and genotyping were repeated where sample volume permitted.

RESULTS

Three samples (2000, 2300, and 61,000 copies/mL) produced reactive results with PRISM. Four samples with viral loads less than 300 copies per mL produced nonreactive results. One sample, originally quantitated at 37,000 copies per mL (but 3850 copies/mL in repeat testing) was also nonreactive by PRISM. Genotyping of this sample indicated a type C genotype with no mutations.

CONCLUSION

Adding serological sensitivity of PRISM CLIA reduced the NAT yield from the original 1: 385,555 to 1:610,488. However, MP HBV NAT still provides additional sensitivity over CLIA, even for a donation with a viral load of almost 4000 copies per mL.

A pilot study for screening blood donors in Taiwan by nucleic acid amplification technology: detecting occult hepatitis B virus infections and closing the serologic window period for hepatitis C virus

BACKGROUND

Blood donors in Taiwan currently are screened for hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) infection by immunoassay. The risk of enzyme immunoassay (EIA)-negative, nucleic acid amplification technology (NAT)-reactive donations is not well understood. This study aimed to screen for such donors in Taiwan by a multiplex test (cobas TaqScreen, Roche) on a commercially available NAT system (cobas s 201 system, Roche).

STUDY DESIGN AND METHODS

NAT was performed on donors without prescreening in pools of six and NAT-reactive pools were then resolved to the single donation. Individual-donor NAT-reactive samples were discriminated by a commercially available polymerase chain reaction (PCR)-based diagnostic assay (COBAS AmpliScreen, Roche). Samples with EIA- and NAT-discordant results were investigated with supplemental serologic and confirmatory tests. Each sample taken from follow-up of HBV NAT yield cases was tested for HBV serologic profile, NAT, and viral load. The sensitivity and performance efficacy were also evaluated.

RESULTS

The 95 percent limit of detection (LOD) for HBV, HCV, and HIV were 5.09, 11.83, and 62.53 IU per mL, respectively. Among 10,727 seronegative donations, 12 HBV NAT yield cases (0.11%) and 1 HCV NAT yield case (0.01%) were detected. Follow-up results for 1 to 8 months showed that the HCV yield case was a window case and all HBV NAT yield cases were occult carriers.

CONCLUSION

The use of NAT detected occult HBV and reduced HCV window period. The yield rate, especially occult HBV, was 10- to 100-fold higher than that in developed, HBV nonendemic countries. Therefore, NAT implementation for routine donor screening in a more cost-effective manner should contribute to safer blood transfusion in Taiwan.

Current risk for transfusion transmitted infections

PURPOSE OF REVIEW

Blood safety is a topic of continuing concern, and much effort is expended on measures to decrease the risk for transmission of infectious agents via transfusion. At the same time, emerging infections may threaten this safety. A periodic review of risk is therefore appropriate.

RECENT FINDINGS

The risk for major transfusion transmissible infections continues to decline as a result of continually strengthening interventions and because of more general improvements in public health. More attention is being paid to emerging infections, and recently donor testing has been implemented for West Nile virus and Trypanosoma cruzi. Within the period covered by this review, the transmission of variant Creutzfeldt-Jakob disease by transfusion has been confirmed. Our understanding of other agents is improving.

SUMMARY

The estimated risk for transfusion transmitted hepatitis viruses and retroviruses is now vanishingly small, but clinicians should be alert to the possibility of infection with emerging infectious agents, because preventive measures may not be available in all cases.

Comparison of two automated nucleic acid testing systems for simultaneous detection of human immunodeficiency virus and hepatitis C virus RNA and hepatitis B virus DNA

BACKGROUND

Recently developed nucleic acid testing (NAT) assays incorporating simultaneous detection of human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B virus (HBV) have made HBV NAT screening more feasible for blood services. This study compared the performance of two "multiplex" NAT assays and their automated testing platforms.

STUDY DESIGN AND METHODS

The HBV NAT yield rate was estimated by testing 10,397 Hong Kong (HK) donor samples concurrently on the PROCLEIX ULTRIO (Ultrio) assay as individual donor samples with the TIGRIS and on the cobas TaqScreen multiplex (cobas MPX) test in pools of 6 with the cobas s 201. Analytical sensitivity was assessed by probit analysis of diluted international standards and operational performance was compared.

RESULTS

Each system detected two different HBV NAT yield samples for a combined rate of 0.04 percent. One additional sample was reactive on the cobas MPX test but remained unresolved. The 95 percent detection limits for HIV-1, HBV, and HCV were 42.2, 12.2, and 2.0 IU per mL, respectively, for Ultrio and 50.5, 8.4, and 6.0 IU per mL for the cobas MPX. The invalid test and failed run rates were 0.05 and 2.92 percent, respectively, for the TIGRIS and 2.39 and 5.53 percent for the cobas s 201.

CONCLUSION

Clinical sensitivity for HBV in HK blood donors was equivalent, as was the analytical sensitivity for HIV-1 and HBV; however, the Ultrio assay had a higher analytical sensitivity for HCV. Despite a shorter downtime and mean time of repair for the cobas s 201, the TIGRIS demonstrated better overall operational performance.

Detection and characterization of hepatitis B virus of anti-hepatitis B core antigen-reactive blood donors in Quebec with an in-house nucleic acid testing assay

BACKGROUND

Hepatitis B virus (HBV) infection can be detected in blood donations by many serologic markers. Since the introduction of routine anti-hepatitis B core antigen (HBc) donor screening at Héma-Québec in April 2003, a large number of donors have been deferred on the basis of reactive anti-HBc test results. The objective of this study was to evaluate the correlation between the anti-HBc-reactive donations and the detection of HBV DNA with an in-house nucleic acid testing (NAT) assay.

STUDY DESIGN AND METHODS

The in-house HBV NAT assay is a conventional polymerase chain reaction amplifying part of the viral S gene. From October 2004 to November 2005, a total of 1169 anti-HBc-reactive donations were tested with this in-house assay. The results were correlated with hepatitis B surface antigen (HBsAg) and anti-HBs markers. HBV DNA-positive samples were further investigated by DNA sequencing.

RESULTS

All HBsAg-positive samples were detected by the NAT assay. Overall, 38 (3.25%) of anti-HBc-positive samples were found to be positive for the presence of HBV DNA. Of these 38, a total of 12 donations with a low level of HBV DNA were HBsAg-negative. The sequencing results clearly showed various genotypes and subtypes within a same genotype.

CONCLUSION

The 3.25 percent HBV DNA positivity rate among the anti-HBc-reactive donations and more particularly the low level of HBV DNA observed in occult donations underline the importance of the use of a sensitive assay to detect HBV DNA in conjunction with other markers. The HBV genetic diversity found in our donor population reflects the province demographics, particularly in the Montreal area where most of the positive donors were from.

Hepatitis B virus DNA-positive, hepatitis B surface antigen-negative blood donations intercepted by anti-hepatitis B core antigen testing: the Canadian Blood Services experience

BACKGROUND

The benefit of introducing anti-hepatitis B core antigen (HBc) screening for intercepting potentially infectious donations missed by hepatitis B surface antigen (HBsAg) screening in Canada was studied.

STUDY DESIGN AND METHODS

Anti-HBc testing of all donations was implemented in April 2005, along with antibody to hepatitis B surface antigen (anti-HBs) and hepatitis B virus (HBV) DNA supplemental testing of anti-HBc repeat-reactive, HBsAg-negative donations. The proportion of potentially infectious donations intercepted by anti-HBc over the initial 18 months of testing was calculated based on three assumptions relating infectivity of HBV DNA-positive units to anti-HBs levels. Lookback was conducted for all DNA-positive donations.

RESULTS

Of 493,344 donors, 5,585 (1.13%) were repeat-reactive for the presence of anti-HBc, with 29 (0.52%) being HBV DNA-positive and HBsAg-negative. The proportion of potentially infectious donations intercepted by anti-HBc screening was 1 in 17,800 if all HBV DNA-positive donations were infectious, 1 in 26,900 if infectivity was limited to donations with an anti-HBs level of not more than 100 mIU per mL, and 1 in 69,300 if only donations with undetectable anti-HBs were infectious. For 279 components in the lookback study, no traced recipients were HBsAg-positive and 7 recipients were anti-HBc-reactive in association with 4 donors, 3 of whom had an anti-HBs level of more than 100 mIU per mL and 1 of whom had a level of 61 mIU per mL.

CONCLUSION

Implementation of anti-HBc screening reduced the risk of transfusing potentially infectious units by at least as much as had been expected based on the literature. The lookback did not provide proof of transfusion transmission of HBV from HBV DNA-positive, anti-HBc-reactive, HBsAg-negative donors but it did not establish lack of transmission either.

HIV-1, HCV and HBV seronegative window reduction by the new Roche cobas® TaqScreen MPX test in seroconverting donors

BACKGROUND

By shortening the pre-seroconversion window in the viral screening of donated blood, nucleic acid amplification testing greatly improves safety and efficiency, particularly when combined with multiple target detection and maximal automation.

OBJECTIVES

Evaluation of seronegative window reduction during HIV-1, HCV and HBV infection by the novel cobas TaqScreen MPX test for simultaneous nucleic acid detection of HIV-1 (groups M and O), HIV-2, HCV and HBV using the cobas s 201 system.

STUDY DESIGN

Testing of HIV-1, HCV, and HBV seroconversion panels (20 each) using the cobas TaqScreen MPX test versus reference immuno- and nucleic acid technology assays.

RESULTS

The cobas TaqScreen MPX test detected HIV-1 and HCV infection earlier than immunoassays in 20/20 and 19/20 panels, and HBV DNA earlier than or on the same day as HBsAg in 19/20 and 18/20 panels, and later in 1 and 2 panels on neat samples and 1:6 dilutions. Pre-seroconversion sensitivity exceeded that of COBAS AmpliScreen testing in pools of 24.

CONCLUSION

The cobas TaqScreen MPX test shortens the pre-seroconversion window in minipools of six, evidencing high sensitivity, and significantly enhances blood-screening efficiency by the simultaneous automated detection of multiple viruses in a single test.

Evaluation of a multiplex human immunodeficiency virus-1, hepatitis C virus, and hepatitis B virus nucleic acid testing assay to detect viremic blood donors in northern Thailand

BACKGROUND

Screening of blood donors with nucleic acid testing (NAT) for human immunodeficiency virus (HIV) and hepatitis C virus (HCV) has been implemented recently in the United States. There are limited data, however, on the additional NAT yield of donors in developing countries in Asia where the prevalence of infection is higher. In addition, data on hepatitis B virus (HBV) NAT in high prevalence areas are minimal.

STUDY DESIGN AND METHODS

A total of 5083 whole-blood donors at the Chiang Mai University Hospital, Thailand, blood bank were evaluated with a commercially available NAT assay (Procleix Ultrio, Gen-Probe, Inc.) to screen individual donations.

RESULTS

No NAT yield cases were found for HIV-1 or HCV. There were 17 samples with discrepant HBV DNA NAT and hepatitis B surface antigen (HBsAg) tests, however. Seven of these were HBV DNA NAT-positive, HBsAg-negative; of these 7, 1 was NAT-positive at baseline, but negative on follow-up, and considered a false-positive, 1 had an acute infection, and 5 had chronic prevalent HBV infections, for a NAT yield of 6 in 4798 HBsAg negative donors (1:800). In addition there were 10 NAT-negative, HBsAg-positive serum samples. All were anti-hepatitis B core antigen immunoglobulin G-positive; on testing with a more sensitive NAT target capture assay, 5 were positive (1.8-20.6 IU/mL) and 5 were negative.

CONCLUSION

Multiplex NAT screening of individual-donor serum samples in Northern Thailand detected approximately 1 per 800 HBV NAT-positive, HBsAg-negative donors. The especially high prevalence of HBV infection in Thailand and other Asian countries suggests that HBV NAT screening of donors will be more cost-effective than in other areas.

Current risks of transfusion-transmitted agents: a review

CONTEXT

Infectious disease testing has dramatically improved the safety of blood for transfusion in the United States, especially since the introduction in 1999 of nucleic acid amplification testing. In 2004, methods (primarily culturing) for detecting bacteria in platelets were also added.

OBJECTIVE

To provide current risk estimates for the likelihood of viral transmission by test-negative blood components and to illustrate the safety improvements since the introduction of bacterial testing of platelets.

DATA SOURCES

Published literature from 1999 through 2006 and unpublished American Red Cross data sources.

CONCLUSIONS

The risk of human immunodeficiency virus and hepatitis C virus transmission through blood transfusion since the introduction of nucleic acid amplification testing is approximately 1 in 2 million. Hepatitis B virus risk, for which nucleic acid amplification testing is not performed routinely, remains at 1 in 200,000 to 500,000 using a combination of anti-hepatitis B core and hepatitis B surface antigen testing. Seven cases of transfusion-transmitted West Nile virus have been reported since the introduction of nucleic acid amplification testing in 2003, but none has been reported since system-wide implementation of processes to increase the test sensitivity for use in epidemic areas. The residual risk of receiving a bacterially contaminated platelet component with clinical consequences is estimated at approximately 1 in 75,000, if culture negative and 1 in 33,000 if not tested by culture methods.

Sensitivity of hepatitis B virus DNA transcription-mediated amplification testing in hepatitis B surface antigen-positive blood donations

BACKGROUND

The objective was to evaluate the performance of nucleic acid testing (NAT) in the detection of hepatitis B virus (HBV) infection in hepatitis B surface antigen (HBsAg)-positive blood donations.

STUDY DESIGN AND METHODS

A total of 253 HBsAg- and anti-hepatitis B core antigen (HBc)-positive samples (50 hepatitis B e antigen [HBeAg]-positive and 203 anti-HBe-positive) from blood donations collected in France were studied. The samples were investigated with a blood screening assay (Procleix Ultrio, Chiron/Gen-Probe) in minipool (MP; x8) and in individual-donation (ID) testing. All nonreactive samples were retested once, and nonreactive MP samples were assayed for viral load (VL).

RESULTS

All 50 HBeAg-positive samples were reactive in MP-NAT and ID-NAT. Of the 203 anti-HBe-positive donations, 80.3 percent were MP- and ID-reactive, 17.2 percent were MP-nonreactive and ID-reactive, and 2.5 percent were nonreactive in ID-NAT. Overall the sensitivity of ID-NAT was 98 percent versus 84 percent for MP-NAT. After retesting, 16 of the 35 MP-nonreactive and/or ID-reactive donations became MP-reactive and 2 of the ID-nonreactive donations became NAT-reactive. The capacity of Procleix Ultrio to detect HBV DNA was not related to HBsAg subtype, but correlated with the VL: the mean VL in the group of MP-nonreactive samples was 1,420 copies per mL vs. 17,000 copies per mL in the group of 40 MP-reactive samples.

CONCLUSION

These results demonstrate that HBV-NAT in ID format is far more effective in detecting viremia in chronic HBsAg carriers than in MP-NAT. The sensitivity of the NAT assay needs to be improved to be considered for replacing the current HBsAg assays, especially when anti-HBc testing is not performed.

Quantification of hepatitis B virus genomes and infectivity in human serum samples

BACKGROUND

Hepatitis B virus (HBV) infections are still a major health issue, with approximately 350 million people chronically infected with HBV worldwide. Information about the minimum copy number of HBV genomes required for infection would be useful as a reference for drug and vaccine development; for monitoring HBV patients during treatment; for screening of blood, organ, and tissue donors; and for regulating nucleic acid amplification assays for HBV.

STUDY DESIGN AND METHODS

Serum samples from chronic carriers (hepatitis B surface antigen-positive and antibody to HBV core antigen-positive) of the three most common subtypes of HBV were studied; their infectivity titers had been evaluated previously in chimpanzees. The genotypes of the HBV samples were determined by DNA sequences and type-specific amino acids of the S gene of HBV. Copy numbers of HBV DNA were quantified by real-time TaqMan polymerase chain reaction (PCR) and by nested PCR applied to limiting dilutions. The copy number determined for each inoculum was compared with previously defined chimpanzee infectivity titers.

RESULTS

The genotypes of the HBV adw, ayw, and adr inocula were A, D, and C, respectively. The concentration of HBV DNA was determined to be 5.4 x 10(9), 2.5 x 10(9), and 3.1 x 10(8) genome equivalents (geq) per mL for serum samples containing the adw, ayw, and adr, respectively. The chimpanzee infectivity titers per milliliter of these initial HBV-containing serum samples were previously determined to be 10(7.5) for adw, 10(7.5) for ayw (MS-2 strain), and 10(8) for adr.

CONCLUSION

The minimal copy number of HBV DNA in chronic carriers of HBV that can infect the chimpanzee model was estimated to be from 3 to 169 geq based upon the three well-characterized inocula.

Hepatitis B virus blood screening: unfinished agendas

The risk of transfusion-transmitted hepatitis B virus (TTHBV) has been steadily reduced through the use of volunteer donors, enhanced donor questioning, and increasingly sensitive hepatitis B surface antigen (HBsAg) tests. In a few countries, screening by antibody to hepatitis B core antigen (anti-HBc) and/or hepatitis B virus (HBV) nucleic acid amplification tests (NAT) has also been introduced. Nevertheless, the risk of TTHBV in most countries is higher than the risk of either human immunodeficiency virus-1 (HIV-1) or hepatitis C virus (HCV). HBV screening practices vary both in terms of the markers screened and the tests employed, and are often dependent on a country's healthcare resources. Anti-HBc screening could be employed as an additional safety feature in HBV low-prevalence countries, but would lead to the rejection of a high percentage of otherwise acceptable donations in HBV moderate- and high-prevalence countries. It has been argued that only individual-donor HBV NAT testing would substantially reduce the risk of TTHBV beyond that achieved by the most sensitive HBsAg tests. However, studies from countries with low, moderate and high HBV prevalence have demonstrated NAT yield from window period- and late stage HBV-infected donors, even using minipool testing following the most sensitive HBsAg tests.

Acute hepatitis B virus window-period blood donations detected by individual-donation nucleic acid testing: a report on the first two cases found and interdicted in Spain

BACKGROUND

Mathematical models predict that, in Spain, a significant number of blood units will be obtained during the window period of the hepatitis B virus (HBV) infection. Routine nucleic acid testing (NAT) on individual blood units may provide experimental data to evaluate such a theoretical risk.

STUDY DESIGN AND METHODS

Between February and July 2005, a total of 34,631 individual units were screened for HBV DNA by a multiplex transcription-mediated amplification (TMA) test. Units that repeatedly reacted in the test, but did not react for HBV surface antigen (HBsAg), were submitted to additional testing by both molecular and conventional assays, and the donors were recalled for follow-up studies and the collection of clinical and epidemiologic data.

RESULTS

Confirmatory testing and follow-up studies identified 2 blood units donated during the HBV infection window period (1/17,316 units studied). Sequencing of amplification products obtained by nested polymerase chain reaction (n-PCR) revealed two HBV strains from genotypes D/ayw3 and F/adw4q-, but did not identify HBsAg mutants. The HBV DNA concentration in the index donations was estimated to be below the n-PCR detection level (180 IU/mL), in both cases. One donor developed acute hepatitis 2 months after donating blood, but the other remained asymptomatic and displayed normal alanine aminotransferase levels at follow-up.

CONCLUSIONS

The HBV infection window period is a real issue in the setting of Spanish blood transfusions. NAT of individual units by TMA would make a significant contribution to improving the safety of the blood supply in Spain. Additional studies involving a larger number of units and longer periods of time are required, however, to ascertain the true incidence of the problem in this country.

Preventing disease transmission by deceased tissue donors by testing blood for viral nucleic acid

Nucleic acid testing (NAT) has reduced the risk of transmitting infectious disease through blood transfusion. Currently NAT for HIV-1 and HCV are FDA licensed and performed by nearly all blood collection facilities, but HBV NAT is performed under an investigational study protocol. Residual risk estimates indicate that NAT could potentially reduce disease transmission through transplanted tissue. However, tissue donor samples obtained post-mortem have the potential to produce an invalid NAT result due to inhibition of amplification reactions by hemolysis and other factors. The studies reported here summarize the development of protocols to allow NAT of deceased donor samples with reduced rates of invalid results. Using these protocols, inventories from two tissue centers were tested with greater than 99% of samples producing a valid test result.