Hepatitis B virus infection and transfusion medicine: science and the occult

T cell responses and viral variability in blood donation candidates with occult hepatitis B infection

BACKGROUND & AIMS

Occult HBV infection (OBI) is defined by the presence of HBV DNA in the liver and/or serum and negative HBsAg testing. Since the implementation of highly sensitive HBV DNA screening, OBI is also detected in healthy blood donors. The aims of this study were to investigate HBV-specific immune responses and genetic variability in donors with OBI, established by HBV DNA in serum.

METHODS

HBV-specific T-cell responses to HBV antigens were tested in 34 OBI donors by IFN-γ ELISpot, cytometric bead array, and intracellular cytokine staining. As comparison populations, 36 inactive HBV carriers, 22 donors with spontaneously resolved HBV infection, 24 vaccinated donors, and 25 seronegative donors were also included. Surface, pre-S, and pre-c/core genes from 44 genotype D isolates (24 OBI and 20 HBsAg-positive) were sequenced.

RESULTS

The immune response of OBI donors to the 3 HBV antigens was 29-41%, similar to the response in subjects with resolved HBV infection and higher than that in HBsAg-positive subjects. On sequence analysis, OBI donors presented a higher HBsAg mutation rate than HBsAg-positive subjects. Mutations were clustered in the major hydrophilic region of HBsAg, and no stop codons or relevant mutations that could affect antigen formation or detection were observed.

CONCLUSIONS

Our results suggest that immune response can suppress viral replication to low levels and HBsAg expression to undetectable levels in OBI blood donors. Relevant mutations were not found in the genomic HBsAg coding region. Hence, the fact that HBsAg was not detected in OBI is likely due to low HBsAg production, rather than to a failure of laboratory reagents.

Significant background rates of HBV and HCV infections in patients and risks of blood transfusion from donors with low anti-HBc titres or high anti-HBc titres with high anti-HBs titres in Japan: a prospective, individual NAT study of transfusion-transmitted HBV, HCV and HIV infections

BACKGROUND

The Japanese Red Cross (JRC) conducted a prospective study to evaluate the frequency of transfusion-transmitted HBV, HCV and HIV infections to assess the risk of transfusion of blood components routinely supplied to hospitals.

STUDY DESIGN AND METHODS

Post-transfusion specimens from patients at eight medical institutes were examined for evidence of infection with HBV (2139 cases), HCV (2091) and HIV (2040) using individual nucleic acid amplification testing (NAT). If these specimens were reactive, pre-transfusion specimens were also examined for the virus concerned by individual NAT. In the event that the pre-transfusion specimen was non-reactive, then all repository specimens from implicated donors were tested for the viruses by individual donation NAT. In addition, a further study was carried out to evaluate the risk of transfusion of components from donors with low anti-HBc titres or high anti-HBc with high anti-HBs titres.

RESULTS

Transfusion-transmitted HCV and HIV infections were not observed. One case of post-transfusion HBV infection was identified (rate, 0·0004675; 95% CI for the risk of transmission, 1 in 451-41,841). The background rates of HBV, HCV and HIV infections in patients prior to transfusion were 3·4% (72/2139), 7·2% (150/2091) and 0% (0/2040), respectively. Sixty-four anti-HBc- and/or anti-HBs-reactive blood components were transfused to 52 patients non-reactive for anti-HBc or anti-HBs before and after transfusion (rate, 0; 95% CI for the risk of transmission, <1 in 22).

CONCLUSION

This study demonstrated that the current criteria employed by JRC have a low risk, but the background rates of HBV and HCV infections in Japanese patients are significant.

Blood donation screening for hepatitis B virus markers in the era of nucleic acid testing: are all tests of value?

BACKGROUND

The American Red Cross implemented hepatitis B virus (HBV) minipool (MP)-nucleic acid testing (NAT) in June 2009, in addition to existing tests for hepatitis B surface antigen (HBsAg) and antibodies to hepatitis B core antigen (anti-HBc). The value of all three tests was evaluated.

STUDY DESIGN AND METHODS

HBsAg, anti-HBc, and HBV DNA (Ultrio MP-NAT, Gen-Probe/Novartis) donation results were analyzed during a 12-month period (July 1, 2009-June 30, 2010). Additional testing by individual-donation (ID) polymerase chain reaction (PCR) to confirm donor infection was performed when any HBV screening test was reactive or positive, except in the case of HBsAg neutralization-positive, anti-HBc-reactive samples. Numbers of blood donations identified as reactive or positive versus nonreactive or negative were compared.

RESULTS

Of about 6.5 million donations, 699 were defined as from HBV-infected donors, of which 64% (444) were reactive for all three markers. More than 99% (697) had reactivity to one or both serologic tests with 68% (477) showing reactivity by MP-NAT. Only two donations were DNA-positive, seronegative NAT-yield donations (1 per 3.23 million), fewer than expected (p = 0.0075). Among MP-NAT-reactive donors, only small numbers represented early infection (2 or 0.4% with negative serology and 10 or 2.1% who were HBsAg confirmed positive, anti-HBc nonreactive). Of the 142 occult HBV-infected donors, 85% were MP-NAT nonreactive requiring ID-PCR for detection (121 or 54.5% of all MP-NAT nonreactives vs. 21 or 4.4% of all MP-NAT reactives).

CONCLUSIONS

The HBV DNA-positive yield rate from MP-NAT was lower than expected, likely representing the rarity of such findings even in very large studies. With the implementation of HBV MP-NAT, the value of maintaining anti-HBc for the detection of low-level HBV DNA-positive donors was confirmed; however, HBsAg screening showed no blood safety value.

Reducing the risk of hepatitis B virus transfusion-transmitted infection

Before 1970, approximately 6% of multi-transfused recipients acquired a transfusion-transmitted Hepatitis B virus (HBV) infection. The safety improvements since then have been tremendous. From a level of a few infections per 1000 donations, the risk today, depending on the screening algorithm and additional measurements performed, has decreased to around 1:500,000 to 1:1,000,000, an improvement greater than 1000-fold compared to 50 years ago. This enormous gain in safety has been achieved through many factors, including development of increasingly more sensitive Hepatitis B antigen (HBsAg) assays; the adoption in some countries of hepatitis B core antibody (anti-HBc) screening; an improved donor selection procedure; HBV vaccination programs; and finally the introduction of HBV nucleic acid testing (NAT). Because there is a tendency in transfusion medicine to add one safety measure on top of another to approach the ultimate goal of zero risks, costs become increasingly a matter of debate. It is obvious that any new measure in addition to existing methods or measures will have very poor cost effectiveness. Therefore each country needs to perform its own calculation based on the country’s own epidemiology, resources, political and public awareness of the risks, in order to choose the correct and most cost-efficient measures. Ideally, each country would make decisions regarding implementation of additional blood safety measures in the context of both the perceived benefit and the allocation of overall health care resources.

An overview of occult hepatitis B virus infection

Occult hepatitis B virus (HBV) infection (OBI), alternatively defined as occult hepatitis B (OHB), is a challenging clinical entity. It is recognized by two main characteristics: absence of HBsAg, and low viral replication. The previous two decades have witnessed a remarkable progress in our understanding of OBI and its clinical implications. Appropriate diagnostic techniques must be adopted. Sensitive HBV DNA amplification assay is the gold standard assay for detection of OBI. Viral as well as host factors are implicated in the pathogenesis of OBI. However, published data reporting the infectivity of OBI by transfusion are limited. Several aspects including OBI transmission, infectivity and its relation to the development of chronic liver diseases and hepatocellular carcinoma have to be resolved. The aim of the present review is to highlight recent data on OBI with a focus on its virological diagnosis and clinical outcome.

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.

Prevalence of occult hepatitis B virus infection

Occult hepatitis B virus (HBV) infection (OBI) is characterized by the persistence of HBV DNA in the liver tissue in individuals negative for the HBV surface antigen. The prevalence of OBI is quite variable depending on the level of endemic disease in different parts of the world, the different assays utilized in the studies, and the different populations studied. Many studies have been carried out on OBI prevalence in different areas of the world and categories of individuals. The studies show that OBI prevalence seems to be higher among subjects at high risk for HBV infection and with liver disease than among individuals at low risk of infection and without liver disease.

Management of occult hepatitis B virus infection: An update for the clinician

Occult hepatitis B virus (HBV) infection (OBI) is defined by the presence of HBV DNA in the liver tissue of individuals who test negative for hepatitis B surface antigen (HBsAg). Patients who have recovered from acute hepatitis B can carry HBV genomes for a long time and show histological patterns of mild necro-inflammation, even fibrosis, years after the resolution of acute hepatitis, without showing any clinical or biochemical evidence of liver disease. At least in conditions of immunocompetence, OBI is inoffensive itself, but when other relevant causes of liver damage are present it might make the course of the liver disease worse. The risk of HBV transmission through transfusion is related to blood donations negative for HBsAg that have been collected during the pre-seroconversion period or during chronic OBI. Use of HBV nucleic acid amplification testing and multivalent anti-HBs antibodies in the HBsAg assays is recommended for detection of true and false OBI, respectively. It is not known if prior hepatitis B immunization with an optimal anti-HBs response in cases of HBV transmission through organ transplantation can effectively modulate or abort the infection. Use of antiviral agents as prophylaxis in patients with serological evidence of past HBV infection prevents reactivation of OBI after transplantation in most cases. Reactivation of OBI has been observed in other conditions that cause immunosuppression, in which antiviral therapy could be delayed until the HBV DNA or HBsAg becomes detectable. OBI might contribute to the progression of liver fibrosis and hepatocellular carcinoma development in patients with chronic liver disease.

Prevalence of antibodies to hepatitis B core antigen and occult hepatitis B virus infections in Korean blood donors

BACKGROUND

This study was performed to determine the prevalence of antibodies to hepatitis B core antigen (anti-HBc) among Korean blood donors and frequencies of hepatitis B virus (HBV) DNA and antibodies to hepatitis B surface antigen (anti-HBs) in anti-HBc-positive donors.

STUDY DESIGN AND METHODS

A total of 12,461 consenting blood donors were consecutively enrolled from Korean Red Cross Blood Services from April to October 2008. All of the donors were screened for anti-HBc with an electrochemiluminescence immunoassay. Repeat-reactive anti-HBc-positive donors were assayed for anti-HBs and for HBV DNA using a multiplex test (Cobas TaqScreen, Roche Molecular Systems) on individual donation.

RESULTS

Of the 12,461 donors, 1682 (13.5%) were reactive for anti-HBc. Among different age groups, there was a steady increase in the anti-HBc-positive rate, ranging from 2.0% in the age group of less than 20 years to 80.0% in the age group of 60 years and older (p<0.0001). Of the anti-HBc-positive donors, 1523 (90.5%) were anti-HBs positive. HBV DNA was detected in two donors who were anti-HBc positive and hepatitis B surface antigen negative. The prevalence of occult HBV infection was 0.016%, and the HBV nucleic acid test (NAT) yield was 1 in 838 (0.12%).

CONCLUSION

This study helps to determine the current status of hepatitis B infection and the prevalence of occult HBV infection in the blood donor population in Korea. We estimate that in Korea, up to 161 units per million donated units from blood donors may contain HBV DNA. Although the potential infectivity of these units has been debated upon, the HBV NAT assay could prevent certain transfusion-transmitted HBV infections.

Nucleic acid testing to detect HBV infection in blood donors

BACKGROUND

The detection of hepatitis B virus (HBV) in blood donors is achieved by screening for hepatitis B surface antigen (HBsAg) and for antibodies against hepatitis B core antigen (anti-HBc). However, donors who are positive for HBV DNA are currently not identified during the window period before seroconversion. The current use of nucleic acid testing for detection of the human immunodeficiency virus (HIV) and hepatitis C virus (HCV) RNA and HBV DNA in a single triplex assay may provide additional safety.

METHODS

We performed nucleic acid testing on 3.7 million blood donations and further evaluated those that were HBV DNA-positive but negative for HBsAg and anti-HBc. We determined the serologic, biochemical, and molecular features of samples that were found to contain only HBV DNA and performed similar analyses of follow-up samples and samples from sexual partners of infected donors. Seronegative HIV and HCV-positive donors were also studied.

RESULTS

We identified 9 donors who were positive for HBV DNA (1 in 410,540 donations), including 6 samples from donors who had received the HBV vaccine, in whom subclinical infection had developed and resolved. Of the HBV DNA-positive donors, 4 probably acquired HBV infection from a chronically infected sexual partner. Clinically significant liver injury developed in 2 unvaccinated donors. In 5 of the 6 vaccinated donors, a non-A genotype was identified as the dominant strain, whereas subgenotype A2 (represented in the HBV vaccine) was the dominant strain in unvaccinated donors. Of 75 reactive nucleic acid test results identified in seronegative blood donations, 26 (9 HBV, 15 HCV, and 2 HIV) were confirmed as positive.

CONCLUSIONS

Triplex nucleic acid testing detected potentially infectious HBV, along with HIV and HCV, during the window period before seroconversion. HBV vaccination appeared to be protective, with a breakthrough subclinical infection occurring with non-A2 HBV subgenotypes and causing clinically inconsequential outcomes. (Funded by the American Red Cross and others.).

Occult hepatitis B virus infection in Thai blood donors

BACKGROUND

An evaluation by the National Blood Center, the Thai Red Cross Society, of two commercial multiplex nucleic acid tests (NATs; the Chiron PROCLEIX ULTRIO test and the Roche Cobas TaqScreen MPX test) for screening Thai blood donors for hepatitis B virus (HBV), hepatitis C virus, and human immunodeficiency virus Type 1 identified 175 HBV NAT-reactive/hepatitis B surface antigen (HBsAg)-negative donors. The classification of the HBV infection of these donors was confirmed by follow-up testing.

STUDY DESIGN AND METHODS

Index samples were tested for HBV serologic markers and HBV viral loads were determined. Donors were followed for up to 13 months and samples were tested with both NAT assays and for all HBV serological markers.

RESULTS

Of 175 HBV NAT-yield donors, 72 (41%) were followed. Based on the follow-up results, the majority of donors who were followed had an occult HBV infection (66.7%), followed by donors with a primary, acute infection (26.4%). The majority of donors in this latter group (20.8%) were in the window period. Three donors (4.2%), who were anti-HBs positive, had a reinfection or breakthrough infection.

CONCLUSION

The majority of donors detected during routine screening, who were HBsAg negative and NAT reactive, had an occult HBV infection, thus validating the decision to introduce NAT for blood donations in Thailand.

Detection of hepatitis B virus DNA among accepted blood donors in Nanjing, China

Background

Posttransfusion hepatitis B virus (HBV) infection still occurs although its incidence has been substantially reduced since the introduction of screening of hepatitis B surface antigen (HBsAg) in blood donors. This study aimed to investigate the occult HBV infection in accepted blood donors in Nanjing, China.

Results

The lower detection limit of the nested PCR in this study was estimated to be 20 copies/ml HBV DNA. The positive rate of occult HBV infection was 0.13% (5 of 2972) in the accepted blood donors. Sequencing data showed that the amplified HBV sequences were not identical each other and to the known sequences cloned in our laboratory, excluding the false-positive caused by cross-contamination. Phylogenetic analysis showed that the HBV in all five donors was genotype B; a single base deletion was detected in the S region of HBV DNA from one donor, and no mutation was observed in the "a" determinant of HBsAg from four other donors. All five donors were negative for anti-HBs and one was positive for anti-HBc.

Conclusions

The prevalence of occult HBV infection in the accepted blood donors in Nanjing, China is relatively high. The data would be meaningful in adapting strategy to eliminate posttransfusion HBV infection in China.

The clinical significance of occult hepatitis B transfusion in Taiwan--a look-back study

OBJECTIVES

A look-back study was conducted to determine the clinical significance of occult hepatitis B virus (HBV) blood transfusion in an HBV hyperendemic area.

AIM

To improve the blood transfusion safety.

BACKGROUND

Occult HBV is transmissible through blood transfusion in HBV-naÏve recipients. However, its impact on recipients with prevalent HBV infection in HBV hyperendemic areas is unclear.

METHODS/MATERIALS

In 2006, 12 occult HBV blood donors were found from 10 824 repository samples by nucleic acid testing. The 74 corresponding recipients were identified and their pre- and post-transfusion clinical information was gathered, and the living recipients were recalled for follow-up. From the available archival sera, the HBV DNA was examined and sub-genomic sequences between paired donor and recipient were compared using polymerase chain reaction-based assays.

RESULTS

Among the 74 recipients, 18 were still alive and 12 returned to our clinic. From the available serological profiles, 76% of recipients had ongoing or recovered HBV infection before transfusion. Only 24 recipients had available post-transfusion serological profiles and none seroconverted to be hepatitis B surface antigen (HBsAg) positive. Moreover, except for the prior HBsAg carriers, the recipients' HBV DNA levels after transfusion were low (<20 IU/mL). One recipient had identical HBV surface gene sub-genomic sequence (384 nucleotides) to his donor. After transfusion, no recipient developed post-transfusion hepatitis (PTH) and the clinical outcome was good.

CONCLUSION

In HBV hyperendemic areas, occult hepatitis B transfusion might not lead to HBsAg carriage or PTH. The risk of transfusion-transmitted HBV infection was probably lower than that in non-endemic areas because most recipients had already experienced HBV infection.

Occult hepatitis B in blood donors in Indonesia: altered antigenicity of the hepatitis B virus surface protein

BACKGROUND AND AIMS

Occult hepatitis B virus infection (OBI) poses a challenge to the safety of blood donation. The prevalence of OBI is not well documented in Indonesia, although this information in such an endemic country is needed. This study was aimed to evaluate the prevalence of occult hepatitis B in blood donors from two cities of Indonesia, and to study the genetic variation and its effect on the predicted antigenicity of HBsAg.

METHODS

Serum samples of 309 regular blood donors negative for HBsAg were tested for anti-HBs and anti-HBc. Hepatitis B virus (HBV) DNA isolated from anti-HBc-positive samples were analyzed by polymerase chain reaction, cloned and sequenced. Antigenic properties of identified HBsAg mutants were predicted by calculation of the antigenic index.

RESULTS

Of the 309 HBsAg-negative samples, anti-HBc was positive in 134 (43.4%) and HBV DNA was detected in 25 (8.1%). Seven of the viremic samples had nucleotide substitutions (A521G, A551T, C582T, and A562G) in the S gene, causing amino acid mutations (T123A, M133L, and T143M) in the 'a' determinant of HBsAg that resulted in changes in the predicted antigenicity.

CONCLUSIONS

OBI was detected in blood donors' samples in Indonesia. Anti-HBc was shown to be a better screening parameter than HBsAg, however, it might result in the loss of donors particularly in endemic countries. HBsAg detection failure in this study might be due to mutations altering the protein antigenicity and/or the low-level carriage of HBV.

The role of anti-core antibody response in the detection of occult hepatitis B virus infection

Occult hepatitis B virus (HBV) infection is characterized by the presence of HBV DNA in serum and/or in the liver of patients negative for hepatitis B surface antigen (HBsAg). Occult infection may impact in several different clinical contexts including the risk of HBV transmission with transfusion or transplantation, and endogenous viral reactivation. The gold standard test for detection of occult infection is the amplification of HBV DNA. However, the serological assay for the long-lasting antibody response to the highly immunogenic HBV core antigen (anti-HBc) represents a qualified candidate as a surrogate for DNA amplification, or for increasing overall sensitivity when assessing the risk of occult hepatitis in peripheral blood. The risk of occult hepatitis associated with anti-HBc seropositivity has been demonstrated extensively, and the presence of antibody response to HBc can be considered a sentinel marker of occult HBV infection.

A 2010 update on occult hepatitis B infection

Occult hepatitis B virus infection is a challenging issue whose virological and clinical relevance has been a source of long-lasting debate. By definition, OBI is characterized by the persistence of HBV-DNA in the liver tissue (and in some cases also in the serum) in absence of HBsAg. According to the HBV serological profile, OBI may be antibody (anti-HBc alone or together with anti-HBs) positive (seropositive OBI) or antibody negative (seronegative OBI). OBI is a complex biological entity with possible relevant clinical implications, mainly related to the intrahepatic persistence of viral cccDNA and to a strong suppression of viral replication and gene expression. Clinical observations suggest that OBI carriers may be a source of HBV transmission through blood transfusion or orthotopic liver transplantation (OLT). The state of suppression of viral replication and gene expression may be discontinued when an immunosuppressive status occurs, leading to typical hepatitis B with severe - and some times - fulminant course. The long-lasting persistence of the virus in the liver may provoke a very mild but continuing necro-inflammation that (if other causes of liver damage cohexist) may contribute over time to the progression of the chronic liver damage towards cirrhosis. In addition, OBI is supposed to be an important risk factor to HCC development since it maintains the pro-oncogenic properties typical of the overt infection.

Occult hepatitis B virus infection: a covert operation

Detection of occult hepatitis B requires assays of the highest sensitivity and specificity with a lower limit of detection of less than 10 IU/mL for hepatitis B virus (HBV) DNA and <0.1 ng/mL for hepatitis B surface antigen (HBsAg). This covert condition is relatively common in patients with chronic hepatitis C virus (HCV) that seems to exert some influence on the replicative capacity and latency of HBV. Detection of virus-specific nucleic acid does not always translate into infectivity, and the occurrence of primer-generated HBV DNA that is of partial genomic length in immunocompetent individuals who have significant levels of hepatitis B surface antibody (anti-HBs) may not be biologically relevant. Acute flares of alanine aminotransferase (ALT) that occur during the early phase of therapy for HCV or ALT levels that remain elevated at the end of therapy in biochemical nonresponders should prompt an assessment for occult hepatitis B. Similarly, the plasma from patients with chronic hepatitis C that is hepatitis B core antibody (anti-HBc) positive (+/-anti-HBs at levels of <100 mIU/mL) should be examined for HBV DNA with the most sensitive assay available. If a liver biopsy is available, immunostaining for hepatitis B surface antigen (HBsAg) and hepatitis B core antigen (HBcAg) should be contemplated and a portion of the sample tested for HBV DNA. This is another reason for optimal collection of a specimen (e.g. two passes with a 16-guage needle under ultrasound guidance). Transmission of HBV to immunosuppressed orthotopic liver transplant recipients by donors with occult hepatitis B (OHB) will continue to occupy the interests of the transplant hepatologist. As patients with OHB may have detectable HBV DNA in serum, peripheral blood mononuclear cells (PBMC) and/or liver that can be reactivated following immunosuppression or intensive cytotoxic chemotherapy, the patient needs to be either monitored or treated depending on the pretreatment serological results such as an isolated anti-HBc reaction or a detectable HBV DNA.

The efficacy of individual-donation and minipool testing to detect low-level hepatitis B virus DNA in Taiwan

BACKGROUND

Financial constraints are the main concern in implementing nucleic acid testing (NAT) as routine blood screening in Taiwan. The PROCLEIX ULTRIO assay (Ultrio) on the TIGRIS System (Novartis Diagnostics) was evaluated for its operational performance both for individual-donation testing (IDT) and in minipools of 4 (MP4) to develop a feasible solution.

STUDY DESIGN AND METHODS

Analytical sensitivity was determined by testing WHO international standards. We tested 10,290 blood donors, 4210 in IDT and 6080 in MP4. Potential hepatitis B virus (HBV) yield donors (hepatitis B surface antigen [HBsAg] negative/NAT reactive) were evaluated for up to 9 months' follow-up. Discordant results between the Ultrio assay and the HBsAg tests were further analyzed by HBV antibody serology, alternative NATs, HBV DNA quantification, and sequencing.

RESULTS

The 95% limits of detection in IU/mL (95% confidence interval) were as follows: human immunodeficiency virus Type 1 (HIV-1), 18 (12-34); hepatitis C virus (HCV), 4.4 (2.8-8.9); and HBV, 6.3 (4.4-11). The retest rates were 0.55% for IDT and 0.33% for MP4. No HIV or HCV yield cases were found, while there were 12 potential HBV yield cases, nine from IDT and three from MP4 testing. Eleven of them were successfully genotyped as B2. Ten of them returned for follow-up and mostly were determined as occult HBV infection (OBI). The IDT yield rate of 9 in 4210 (0.21%) was fourfold greater than the MP4 yield rate of 3 in 6080 (0.05%; p < 0.05).

CONCLUSION

The higher yield rate for IDT versus MP4 demonstrates the benefit to implement a more sensitive NAT strategy in regions having significant OBI carriers such as Taiwan.

Current challenges in viral hepatitis, antimicrobial resistance and the influenza pandemic

The 3rd Ditan International Conference on Infectious Diseases was held from 29 July to 2 August 2009 at the Beijing International Conference Center, Beijing, China. Over 1000 participants from 27 countries attended the 4-day conference, titled 'World Dialogue on Infectious Diseases'. A broad range of topics were covered this year, including TB, methicillin-resistant Staphylococcus aureus, HIV, influenza and gastrointestinal infections. In addition, there was a particularly strong focus on two contrasting topics of viral hepatitis and antibiotic resistance, which is the focus of this meeting report.

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.