Occult hepatitis B virus infection in Thai blood donors

Blood Donation Screening of Transfusion-Transmissible Viral Infection Using Two Different Nucleic Acid Testing (NAT) Platforms: A Single Tertiary Care Oncology Centre Experience

Nucleic acid testing (NAT) is used to screen transfusiontransmittable infections (TTIs) in donated blood samples and provide an additional layer of blood safety. In this study, we describe our experience in screening viral TTIs using two formats of NAT: cobas® MPX2 polymerase chain reaction- based minipool NAT (PCR MP-NAT) and Procleix Utrio Plus transcription-mediated amplificationbased individual donor-NAT (TMA ID-NAT). Data routinely collected as a part of blood bank operations were retrospectively analysed over a period of 70 months for TTIs. Blood samples were initially screened for HIV, HBV, HCV, syphillis by chemiluminescence and malaria by Rapid card test. In addition to serological testing, all samples were further screened by TMA-based ID-NAT (ProcleixUltrio Plus Assay) during Jan 2015-Dec 2016, and by PCR-based MP-NAT (Cobas® TaqScreen MPX2) during Jan 2017-Oct 2020. RESULTS: A total of 48,151 donations were processed over 70 months, of which 16,212 donations were screened by ProcleixUtrio Plus TMA ID-NAT and 31,939 donations by cobas® MPX2 PCR MP-NAT. Replacement donors and male donors outnumbered voluntary donors and female donors respectively. The overall NAT yield rate of MP-NAT was 1:2281 compared to 1:3242 with ID-NAT, during the respective time period. ID-NAT detected 5 HBV infections missed by serology, whereas MP-NAT detected 13 HBV infections and 1 HCV infection missed by serology. The proportion of donations that were both seroreactive and NAT reactive was higher with MP-NAT (59.8%) compared to ID-NAT (34.6%). Cobas® MPX2MP-NAT had higher overall NAT yield rate compared to ProcleixUtrio Plus ID-NAT and confirmed a higher proportion of seroreactive donations. Due to the ease of operation, simple algorithm, cobas® MPX2 PCR based MP-NAT can be an effective solution for blood screening in India.

Comparative analysis of hepatitis B virus infections in blood donors born before and after the implementation of universal HBV vaccination in southern China

BACKGROUND

In China, the vaccinated blood donors have rapidly increased by recent years, which may impact blood safety. The true prevalence of HBV between vaccinated blood donors and non-vaccinated blood donors should be explored.

STUDY DESIGN AND METHODS

The samples of blood donors were collected and detected for serologic markers of HBV in the Shenzhen Blood Centre (SZBC). The discrepant results were tested with commercial electrochemiluminescence immunoassay (ELCI) for HBsAg, anti-HBs, HBeAg, Anti-HBe and Anti-HBc, alternative MPX ID NAT, nested PCR, and a quantitative real-time polymerase chain reaction (qPCR) assay for HBV DNA. The serological and molecular characteristics of HBV infected blood donors were analysed, and the effects on blood safety for donors born before and after the implementation of universal HBV vaccination were compared.

RESULTS

Out of 242 presumed HBV infected donors from 26 318 donations, 131 (0.49%, [95% CI, 0.43-0.59]) chronic HBV infections (CHB, HBsAg detected with or without DNA), 58 (0.22%, [95% CI, 0.17-0.28]) occult hepatitis B infections (OBI, HBsAg not detected, assume anti-HBc positive and/or anti-HBs with HBV DNA) and 3 (0.011%, [95% CI, 0.0023-0.033]) window period (WP) infections were confirmed respectively. There were 28 CHBs (0.44%), 7 OBIs (0.11%) and 1 WP (0.016%) from vaccinated blood donor and 103 CHBs (0.52%), 51 OBIs (0.26%) and 2 WPs (0.01%) from non-vaccinated blood donor. The HBV+ (CHBs, OBIs and WPs) rate (0.56%) in vaccinated donors was lower than in non-vaccinated donors (0.78%, p < 0.05). The HBsAg titers of vaccinated infected blood donors (Median: 128.8 IU/ml) were much higher than non-vaccinated infected blood donors (58.4 IU/ml). The OBI yield rates in the vaccinated blood donors was significantly lower than the non-vaccinated blood donors (p < 0.05). There 102/124 (82.3%) samples were genotype B, 22/124 (17.7%) were genotype C respectively. There was no significant difference in the distribution of genotype between non-vaccinated blood donors (B/C, 86/17) and vaccinated blood donors (B/C, 23/6; p > 0.05). High frequency of vaccine escape mutations M133L (32.4%) and E164G in S region of genotype B strains and substitution L175S (40.9%) related to vaccine escape in S region of genotype C strains were identified.

CONCLUSION

The universal HBV vaccination program markedly reduces the risk of HBV infection in blood donors, and provides a significant guarantee for the safety of blood transfusion. Several important mutations detected related vaccine escape and notable mutations needed further investigated.

High-Frequency Notable HBV Mutations Identified in Blood Donors With Occult Hepatitis B Infection From Heyuan City of Southern China

Background

All Chinese blood centers have implemented mini pool (MP) HBV nucleic acid testing (NAT) together with HBsAg ELISA in routine donor screening since 2015. The prevalence of occult hepatitis B virus infection (OBI) in donors from different regions varies, and the molecular characterization of the HBV DNA and clinical outcomes of these OBIs remain largely unexplored.

Methods

Blood donations from Heyuan city in Southern China were screened by HBsAg ELISA and HBV MP8 NAT. Donations with HBsAg-/HBV DNA+ were collected for this study. Molecular characterizations of HBV DNAs were further analyzed by various DNA amplification assays including quantitative PCR (qPCR) and nested PCR, amplifying the basic core and pre-core promoter regions (BCP/PC). The HBsAg (S) region from HBV DNA was isolated by high-volume nucleic acid extraction. Notable mutations were identified by comparison to the HBV reference sequences. The clinical outcomes of the donors with OBIs were further followed for nearly 3 years.

Results

Seventy OBIs from 44,592 donations (0.15%) that we identified and reported previously were enrolled for this current study. HBV sequences were obtained from 44/70 OBIs, and genotyping analysis showed that 42/44 (95.2%) OBIs were genotype B, and 2/44 (4.8%) were genotype C. Interestingly, mutation analysis revealed that various mutations including M133L/T, F134L, P142L, V168A, R169H, S174N, L175S, and V177A of HBV DNA affecting HBsAg detection were observed in genotype B OBIs. Two notable mutations, T47K and L53S, were identified in genotype C OBIs. Follow-up studies showed that 3/31 (9.7%) OBIs converted to HBsAg+ as chronic infections while 1/31 (3.2%) HBV DNA was undetectable (classified as recovery) and 27/31 (87.1%) remained as OBIs.

Conclusion

Various notable mutations affecting HBsAg detection were observed in blood donors with OBIs in Heyuan city of Southern China. Follow-up studies showed that most OBIs remained as OBIs with fluctuating or low viral loads. Higher sensitive HBV ID NAT is recommended for donor screening to further reduce the transmission risk of OBIs.

The impact of nucleic acid testing to detect human immunodeficiency virus, hepatitis C virus, and hepatitis B virus yields from a single blood center in China with 10-years review

BACKGROUND

Since 2010, the Blood Center of Zhejiang province, China, has conducted a pilot nucleic acid amplification testing (NAT) screening of blood donors for Hepatitis B virus (HBV), Hepatitis C virus (HCV), and Human immunodeficiency virus (HIV). This study aims to assess the results of NAT testing over 10 years to establish the effects and factors influencing NAT yields of HBV, HCV, and HIV.

METHODS

Blood donations from seven different blood services were screened for HBV DNA, HCV RNA, and HIV RNA using 6 mini pools (6MP) or individual donation (ID)-NAT method between August 1, 2010, and December 31, 2019, at the NAT centralized screening center. We compared 3 transcription-mediated amplification (TMA) assays and 2 polymerase chain reaction (PCR) assays. Further, HBV, HCV, and HIV NAT yields were calculated and donor characteristics and prevalence of HBV NAT yields analyzed. Donors with HCV and HIV NAT yield were also followed up.

RESULTS

1916.31 per million donations were NAT screening positive overall. The NAT yields for HBV, HCV, HIV and non-discriminating reactive were 1062.90 per million, 0.97 per million, 1.45 per million, and 850.99 per million, respectively, which varied in the seven blood services and different years. HBV NAT yields were higher than those of HCV and HIV and varied across demographic groups. Risk factors included being male, old age, low education level, and first-time donors. We found no differences in NAT yields of HBV, HCV, and HIV between the 3 TMA and 2 PCR assays; nonetheless, statistically, significant differences were noted between the five assays.

CONCLUSION

In summary, NAT screening in blood donations reduces the risk of transfusion-transmitted infections and shortens the window period for serological marker screening. Therefore, a sensitive NAT screening method, ID-NAT workflow, and recruitment of regular low-risk donors are critical for blood safety.

Sensitivity and specificity of a new automated system for the detection of hepatitis B virus, hepatitis C virus, and human immunodeficiency virus nucleic acid in blood and plasma donations

BACKGROUND

Use of nucleic acid testing (NAT) in donor infectious disease screening improves transfusion safety. Advances in NAT technology include improvements in assay sensitivity and system automation, and real-time viral target discrimination in multiplex assays. This article describes the sensitivity and specificity of cobas MPX, a multiplex assay for detection of human immunodeficiency virus (HIV)-1 Group M, HIV-2 and HIV-1 Group O RNA, HCV RNA, and HBV DNA, for use on the cobas 6800/8800 Systems.

STUDY DESIGN AND METHODS

The specificity of cobas MPX was evaluated in samples from donors of blood and source plasma in the United States. Analytic sensitivity was determined with reference standards. Infectious window periods (WPs) before NAT detectability were calculated for current donor screening assays.

RESULTS

The specificity of cobas MPX was 99.946% (99.883%-99.980%) in 11,203 blood donor samples tested individually (IDT), 100% (99.994%-100%) in 63,012 donor samples tested in pools of 6, and 99.994% (99.988%-99.998%) in 108,306 source plasma donations tested in pools of 96. Seven HCV NAT-yield donations and one seronegative occult HBV infection were detected. Ninety-five percent and 50% detection limits in plasma (IU/mL) were 25.7 and 3.8 for HIV-1M, 7.0 and 1.3 for HCV, and 1.4 and 0.3 for HBV. The HBV WP was 1 to 4 days shorter than other donor screening assays by IDT.

CONCLUSION

cobas MPX demonstrated high specificity in blood and source plasma donations tested individually and in pools. High sensitivity, in particular for HBV, shortens the WP and may enhance detection of occult HBV.

Screening and diagnosis of HBV in low-income and middle-income countries

HBV testing and diagnosis of HBV-related liver disease in low-income and middle-income countries differs substantially from that in developed countries in terms of access to resources and expensive technologies requiring highly specialized staff. For identification and classification of HBV infection, genomic amplification methods to detect and quantify HBV DNA are often nonexistent or available only in central laboratories of major cities. When samples from peripheral locations do arrive, delays in receiving results generate loss to follow-up. Testing is often limited to measurement of hepatitis B surface antigen (HBsAg), alanine aminotransferase levels, aspartate aminotransferase to platelet ratio index and hepatitis B e antigen (HBeAg) to determine indications for antiviral therapy (AVT). Utilization of AVT is limited by cost and availability, particularly when patients are not covered by health insurance. The natural history of HBV infection is influenced by genotypes B and C in East Asia, where decades of immune tolerance have led to mostly vertical transmission; in sub-Saharan Africa, where genotypes A1 and E predominate, infection is transmitted horizontally between young children, followed by a nonreplicative phase. In both regions, cirrhosis and hepatocellular carcinoma are common and would be considerably ameliorated by AVT. Implementation of the HBV vaccine since the 1990s in Asia and 2000s in Africa has decreased the incidence of HBV, but vaccine failure and insufficiently effective prevention remain concerning issues.

Automated Triplex (HBV, HCV and HIV) NAT Assay Systems for Blood Screening in India

This review is confined to triplex nucleic acid testing (NAT) assays to be used on fully automated platform. Around the world, these assays are being used at various transfusion medicine centres or blood banks to screen blood units for HBV, HCV and HIV. These assay systems can screen up to 1000 blood units for HBV, HCV and HIV simultaneously in a day. This area has been dominated by mainly two manufacturers: M/s Gen-Probe-Novartis and M/s Roche Molecular Systems. The triplex NAT assay systems of both manufacturers are licensed by United States Food and Drug Administration. There is not much awareness about the technology and procedures used in these assays. The main objective of this review is to create awareness about the technology and procedure of these assays.

Impact of nucleic acid amplification test on screening of blood donors in Northern Pakistan

BACKGROUND

The Armed Forces Institute of Transfusion located in Rawalpindi, Northern Pakistan, acts as a regional blood center with more than 50,000 donations collected annually. Nucleic acid amplification testing (NAT) was introduced in our institution in September 2012 for screening all seronegative blood donors.

STUDY DESIGN AND METHODS

The study was conducted from September 21, 2012, to September 20, 2013. Samples from the seronegative donors were run on cobas s 201 platform (Roche) in pools of six. Reactive donors were followed up for further confirmatory testing to rule out false-positive results. Viral load estimation was done for all NAT-reactive donors.

RESULTS

After serologic screening of 56,772 blood donors, 2334 were found to be reactive; 719 (1.27%) were reactive for hepatitis B surface antigen, 1046 (1.84%) for antibody to hepatitis C virus (anti-HCV), 12 (0.02%) for antibody to human immunodeficiency virus, and 557 (0.98%) for syphilis antibodies. A total of 27 NAT-reactive donors were confirmed after testing 54,438 seronegative donors, with an overall NAT yield of one in 2016 donors: 23 for hepatitis B virus (HBV) DNA (HBV NAT yield, 1:2367) and four for HCV RNA (HCV NAT yield, 1:13,609). The residual risk after NAT implementation, calculated for the first-time blood donors, was 62.5 and 4.4 per million donors for HBV and HCV, respectively.

CONCLUSIONS

NAT has improved the safety of blood products at our transfusion institution. Confirmation of NAT results must always be done either on follow-up samples or on samples from the retrieved frozen plasma bag.

The outcomes of kidney transplantation in hepatitis B surface antigen (HBsAg)-negative recipients receiving graft from HBsAg-positive donors: a retrospective, propensity score-matched study

The outcomes of kidney transplantation (KT) from hepatitis B surface antigen-positive [HBsAg(+)] donors to HBsAg(-) recipients remain inconclusive, possibly due to substantial differences in methodological and statistical models, number of patients, follow-up duration, hepatitis B virus (HBV) prophylactic regimens and hepatitis B surface antibody (anti-HBs) levels. The present retrospective, longitudinal study (clinicaltrial.gov NCT02044588) using propensity score matching technique was conducted to compare outcomes of KT between HBsAg(-) recipients with anti-HBs titer above 100 mIU/mL undergoing KT from HBsAg(+) donors (n = 43) and HBsAg(-) donors (n = 86). During the median follow-up duration of 58.2 months (range 16.7-158.3 months), there were no significant differences in graft and patient survivals. No HBV-infective markers, including HBsAg, hepatitis B core antibody, hepatitis B extracellular antigen and HBV DNA quantitative test were detected in HBsAg(+) donor group. Renal pathology outcomes revealed comparable incidences of kidney allograft rejection while there were no incidences of HBV-associated glomerulonephritis and viral antigen staining. Recipients undergoing KT from HBsAg(+) donors with no HBV prophylaxis (n = 20) provided comparable outcomes with those treated with lamivudine alone (n = 21) or lamivudine in combination with HBV immunoglobulin (n = 2). In conclusion, KT without HBV prophylaxis from HBsAg(+) donors without hepatitis B viremia to HBsAg(-) recipients with anti-HBs titer above 100 mIU/mL provides excellent graft and patient survivals without evidence of HBV transmission.

Genetic characterization and genotyping of hepatitis B virus (HBV) isolates from donors with an occult HBV infection

BACKGROUND AND OBJECTIVES

Screening of Thai blood donors has resulted in the detection of donors with an occult HBV infection (OBI), where HBsAg is undetectable, but hepatitis B virus (HBV) DNA is present in serum in low concentrations. This study was designed to determine whether the occurrence of OBI in donors was linked to the HBV genotype and possibly to mutations in the surface (S) and core (C) gene regions.

MATERIALS AND METHODS

Mutations in the S and C gene regions in 48 Thai donors with OBI were mapped by sequencing. Genotyping was determined with the INNO-LiPA test and by phylogenetic analysis of sequences from the S and C genes.

RESULTS

The majority of OBI samples were genotype C (81·3%) with 6·3% of samples being genotype B. In addition, two genotype I isolates were identified. Mutations in the S region (100%) were found especially in loop 1 of the major hydrophilic loop (MHL) at positions I110L, T114S, T126I and S113T, whereas mutations in the C region (65%) were within the basal core promoter region (position A1762T/G1764A) and precore region (position G1896A).

CONCLUSION

The majority of OBI samples were HBV genotype C, although genotype I, which is newly emerging in Thailand, was also detected. The study demonstrated that OBI was probably not associated with a particular HBV genotype or with certain mutations in the S and C gene regions. However, mutations in the C gene region which could potentially impair viral replication and HBsAg production and potentially lead to OBI were identified.

Hepatitis B virus nucleic acid amplification testing of Australian blood donors highlights the complexity of confirming occult hepatitis B virus infection

BACKGROUND

We present an analysis of the first 2 years of hepatitis B virus (HBV) nucleic acid testing (NAT) of the Australian donor population.

STUDY DESIGN AND METHODS

Between July 5, 2010, and July 4, 2012, all blood donations were screened for HBV DNA and hepatitis B surface antigen (HBsAg). Donors who tested HBsAg negative but HBV NAT positive were assessed as occult hepatitis B infections (OBI) if reactive for antibodies to HBV core antigen (anti-HBc). Donors who were anti-HBc reactive but with nonrepeatable or nondiscriminated NAT results were assessed as HBV inconclusive pending follow-up testing.

RESULTS

During the study period a total of 2,673,521 donations were screened for HBV. Forty-two chronic OBI infections (5.55/100,000 donors) were identified compared to eight acute serologic window period infections (1.06/100,000 donors). Of the 42 OBI cases, 23 (54.8%) were detected the first time they were screened for HBV DNA while 19 (45.2%) gave one or more HBV NAT-nonreactive results before detection. Of 68 donors initially assessed as HBV inconclusive and available for follow-up, 10 later confirmed as OBI cases while 51 were NAT nonreactive but remained anti-HBc reactive and OBI could not be excluded.

CONCLUSION

This study demonstrated a substantially higher prevalence of OBI compared to acute serologic window period HBV infections in Australian blood donors. Follow-up testing of OBI cases indicates that HBV DNA is often only intermittently detectable in OBI, highlighting the importance of including anti-HBc to optimize the HBV testing algorithm.

Six-year pilot study on nucleic acid testing for blood donations in China

A six-year pilot study on nucleic acid testing for HBV, HCV and HIV-1 has been undertaken on sero-negative plasmas in mini-pool and individual donation testing at Shenzhen Blood Center. Of 307,740 sero-negative blood samples, 95 of 102 HBV DNA yields were confirmed positive, 80/95 (84.2%) were classified as occult HBV infection (OBI) and 15 (15.8%) as window period cases. Amongst OBIs, 45% carried anti-HBc only, 41.3% anti-HBc and anti-HBs and 13.7% anti-HBs only. HBV DNA yield was 1:3239. One HCV WP and one HIV-1 infected donations were detected. High residual risk was found in current blood donations screening in China.

Occult hepatitis B infections among blood donors in Lao PDR

BACKGROUND AND OBJECTIVES

In Lao People's Democratic Republic, hepatitis B virus is highly endemic. However, blood donations are only screened for HBsAg, leaving a risk of transmission by HBsAg-negative occult infected donors. Here, we characterized first-time blood donors to assess prevalence of hepatitis B virus infections and occult infected donors.

MATERIALS AND METHODS

Sera were screened for HBsAg, HBeAg and anti-HBs, anti-HBc and anti-HBe antibodies. Occult HBV infections (OBIs) were assessed in HBsAg-negative sera by PCR, and sera of HBsAg positive and occult infected donors were phylogenetically characterized.

RESULTS

9·6% of the donors were HBsAg positive, and 45.5% were positive for at least one of the hepatitis B virus serum markers. More than 40% HBsAg carriers were HBeAg positive, with HBeAg seroconversion occurring around 30 years of age. Furthermore, 10·9% of HBsAg-negative, anti-HBc and/or anti-HBs-positive donors were occult infected with hepatitis B virus. Thus, at least 3·9% of blood donations would potentially be unsafe, but hepatitis B virus DNA copy numbers greatly varied between donors.

CONCLUSION

In Lao People's Democratic Republic, a sizable proportion of HBsAg-negative and anti-HBc antibody-positive blood donations are potentially DNA positive and infective for hepatitis B.

Detection and identification of occult HBV in blood donors in Taiwan using a commercial, multiplex, multi-dye nucleic acid amplification technology screening test

BACKGROUND

The ability of a new generation commercial, multiplex, multi-dye test from Roche, the cobas TaqScreen MPX test, version 2.0, to detect and identify occult HBV infections was evaluated using routine donor samples from Kaohsiung Blood Bank, Taiwan.

STUDY DESIGN AND METHODS

A total of 5973 samples were tested by nucleic acid amplification technology (NAT); 5898 in pools of six, 66 in pools of less than six and nine samples individually. NAT-reactive samples were retested with alternative NAT tests, and follow-up samples from the donors were tested individually by NAT and for all the HBV serological markers.

RESULTS

Eight NAT-only-reactive donors were identified, and follow-up samples were obtained from six of the donors. The results indicated that all eight donors had an occult HBV infection with viral loads <12 IU/ml.

CONCLUSION

The cobas(®) TaqScreen MPX test, version 2.0, has an advantage over the current Roche blood screening test, the cobas TaqScreen MPX test, for screening donations in countries with a high prevalence of occult HBV infections since the uncertainty associated with identifying samples with very low viremia is removed by the ability of the test to identify the viral target in samples that are reactive with the cobas TaqScreen MPX test, version 2.0.

Sensitivity of individual-donation and minipool nucleic acid amplification test options in detecting window period and occult hepatitis B virus infections

BACKGROUND

Several comparison studies showed that the Ultrio assay (Novartis Diagnostics) used in individual-donation nucleic acid amplification testing (ID-NAT) format was as sensitive as the TaqScreen assay (Roche) on minipools of six donations (MP6), but the sensitivity of HBV DNA detection has been improved in the new Ultrio Plus version of the assay. A head-to-head comparison study was designed to compare the clinical sensitivity of the Ultrio and Ultrio Plus assay in ID, MP4, and MP8 formats using TaqScreen MP6 as a reference assay.

STUDY DESIGN AND METHODS

Plasma samples of 107 hepatitis B surface antigen (HBsAg)-negative, HBV ID-NAT (Ultrio) positive-yield samples and 29 HBV DNA-negative, HBsAg-positive samples were used for comparison of NAT options in replicate testing of dilutions. Viral loads and relative sensitivities were determined by probit analysis against the Eurohep standard.

RESULTS

Ultrio Plus detected a significantly (p < 0.00001) higher proportion of replicate assays on HBV NAT yields (77%) than Ultrio ID (62%) and TaqScreen MP6 (47%), whereas Ultrio Plus MP4 and MP8 detected 53 and 41%, respectively. On HBsAg-yield samples missed by Ultrio screening, the reactivity rate increased significantly (p < 0.0001) from 23% in Ultrio to 65% in Ultrio Plus and further to 72% (p = 0.10) in the TaqScreen assay. The overall improvement factor of the analytical sensitivity offered by the target enhancer reagent in the Ultrio Plus assay was 2.5 (2.0-3.1)-fold on the Ultrio yield samples, but 43 (11-350)-fold on the HBsAg yields. In ID-NAT format the analytical sensitivity of TaqScreen relative to Ultrio Plus was 2.0 (1.0-4.2), 0.9 (0.7-1.3), and 1.6 (0.9-3.0) on the Eurohep standard, HBV NAT-, and HBsAg-yield samples respectively.

CONCLUSION

The clinical sensitivity of the currently available commercial NAT methods is mainly driven by the pool size.

Comparative analysis of triplex nucleic acid test assays in United States blood donors

BACKGROUND

This study assessed the clinical sensitivity of three fully automated, human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B virus (HBV) triplex nucleic acid test (NAT) assays by individual donation (ID-NAT) and at operational minipool (MP-NAT) sizes used worldwide.

STUDY DESIGN AND METHODS

MPX, Ultrio, and Ultrio Plus were used to test 2222 pedigreed, marker-positive samples with varying viral loads, each from a unique US blood donor. NAT-positive, seronegative yield samples (16 HBV, 156 HCV, and 23 HIV) were tested in replicates of three; undiluted; and in 1:6, 1:8, and 1:16 dilutions (MP6, MP8, and MP16), simulating various MP sizes. Seropositive samples (1276 HBV, 488 HCV, and 263 HIV) were tested by ID-NAT in singlet.

RESULTS

MPX-MP6 and Ultrio Plus-MP16 had equivalent HCV sensitivity. Although Ultrio Plus-MP16 for HIV trended toward lesser sensitivity, this was not corroborated in a large substudy of low-viral-load samples in which Ultrio Plus-MP8/MP16 showed 100% reactivity. MPX-ID and Ultrio Plus-ID HBV clinical sensitivity were identical, but MPX-MP6 was significantly more sensitive than Ultrio Plus-MP16; the differential yield projected to one HBV NAT yield per 4.72 million US donations. Ultrio Plus HBV sensitivity did not increase at MP8 versus MP16. Ultrio Plus versus Ultrio sensitivity was significantly increased in HBV-infected donors with early acute, late acute or chronic, and occult infections. No difference in sensitivity was noted for any virus for MPX-MP6 versus Ultrio Plus-ID.

CONCLUSIONS

Our data support US donation screening with MPX-MP6 or Ultrio Plus-MP16 since the HBV DNA detection of Ultrio Plus was significantly enhanced (vs. Ultrio) without compromising HIV or HCV RNA detection.

Enhanced detection of hepatitis B virus in Hong Kong blood donors after introduction of a more sensitive transcription-mediated amplification assay

BACKGROUND

A total of 517,072 and 399,326 consecutive donations were screened for hepatitis B virus (HBV) by individual-donation nucleic acid testing (ID-NAT) using Ultrio and Ultrio Plus assays (Novartis Diagnostics), respectively. The impact of more sensitive HBV detection by the latter assay version was established by comparing NAT yield and transmission risk.

STUDY DESIGN AND METHODS

Donations were screened simultaneously for HBV serologic markers and ID-NAT, followed by discriminatory assay and confirmatory test algorithms. Window period (WP) reduction and residual HBV transmission risk were computed using mathematical modeling.

RESULTS

HBV NAT-yield rates for both WP and occult HBV infection (OBI) increased significantly from 1:34,471 to 1:17,362 (p = 0.036) and from 1:5120 to 1:2450 (p < 0.0001), despite a 1.2- and 1.6-fold decrease in hepatitis B surface antigen (HBsAg) incidence and prevalence rates respectively. After adjusting for this bias, the WP and OBI NAT-yield improvement factors were 2.3 and 3.4, respectively, higher than a less than 1.5-fold increase estimated from analytical sensitivity studies on HBV Genotype A and C standards. The current WP transmission risk with Ultrio Plus screening was estimated at 1:55,000 compared to 1:22,000 with HBsAg testing.

CONCLUSION

The observed greater than twofold enhanced WP NAT yield with the Ultrio Plus assay can be explained by greater than 10-fold increased analytical sensitivity in detecting the HBV Genotype B and C strains in Hong Kong. Direct comparison studies of the two assay versions on dilutions of HBV NAT-yield samples are required to confirm this hypothesis.

Hepatitis B virus in transfusion medicine: still a problem?

Hepatitis B virus (HBV) has probably evolved with humans for nearly 35,000 years. HBV diversified into 9 genotypes (A-I) presenting specific features directing epidemiology, clinical expression and testing. Genotypes E and C are more infectious and carry higher risk of chronicity and cancer. HBsAg blood screening implemented 40 years ago enormously decreased the risk of transfusion transmission but the remaining risk requires extremely sensitive nucleic acid testing (NAT) to be removed. Limitations of the host immune system, the impact of immunodeficiency and the mechanisms utilised for viral persistence were recently identified. HBV replication produces excess HBsAg and infectious and defective viral particles but screening assays for HBsAg or viral particles alone do not allow fully efficient detection, making necessary screening for both. The host immune system fails to completely control the virus that escapes and persists unrecognized at very low levels or as immuno-selected variants. Variants may not be identified by assays, explaining false negative results. Specific mutations may affect post-transcriptional mechanisms including HBV RNA splicing. Asymptomatic HBV infected blood donors are at risk of long-term complications through mechanisms to be understood for appropriate counselling. Infectivity of occult HBV infection (OBI) by transfusion appears low, anti-HBc (anti-core antigen) only being more infectious than anti-HBs (anti-S protein) positive units.

Challenges in hepatitis B detection among blood donors

PURPOSE OF REVIEW

The availability of hepatitis B virus (HBV) nucleic acid testing (NAT) for donor blood screening led to its implementation in low prevalence and high prevalence countries. Genomic detection was a substantial addition to HBV surface protein (HBsAg) screening by detecting window period infections and 'occult' HBV infections (OBIs), characterized by undetectable HBsAg, low viral load and presence of serological markers (anti-HBc and/or anti-HBs). OBIs are the result of multiple, poorly understood mechanisms including incomplete immune control mutations of the HBsAg antigenic determinants; abnormal expression of S gene; and inhibition of genome transcription. Infectivity for the recipient is high for window period blood and relatively low for OBIs.

RECENT FINDINGS

The number of cases identified by NAT ranges between 1 : 1000 and 1 : 50 000, depending on epidemiology and assay sensitivity whether NAT is implemented in individual donations or pools of samples. OBI donors are generally older than 45 years except in Africa, carry very low viral load (median 11-25  IU/ml) and have normal alanine transaminase levels. Cases carrying anti-HBc alone are more infectious than those with low level of anti-HBs. Evidence of HBsAg escape mutants that are undetected by commercial assays has been published. Inhibition of HBsAg mRNA production and export are potential mechanisms of OBI occurrence.

SUMMARY

HBV blood safety is improved by NAT for HBV DNA when applied to individual donations. Until the sensitivity of NAT is improved, both this method and HBsAg screening are needed to eliminate potentially infectious blood donations. Occult HBV characterization clarifies new facets of HBV natural history.