A method for estimating the residual risk of transfusion-transmitted HBV infection associated with occult hepatitis B virus infection in a donor population without universal anti-HBc screening

Hepatitis B infections among blood donors in England between 2009 and 2018: Is an occult hepatitis B infection a risk for blood safety?

INTRODUCTION

Hepatitis B virus (HBV) is one of the most frequent infections identified in blood donors in England and represents an ongoing blood safety risk. We have analyzed markers of HBV infections in blood donors in England between 2009 and 2018 and used these to estimate the likelihood of non-detection of occult HBV infection (OBI).

METHODS

We collected epidemiological, virological, and genotyping information on HBV cases identified in England, 2009-2018. The estimated risk of non-detection and likely transmission of OBI were compared to lookback and transfusion-transmitted infections surveillance data.

RESULTS

Six-hundered and fifty-five HBV-infected blood donors were identified in England during the 10-year period; 598 chronic, 32 acute, and 25 occult HBV infections. However, most donors with chronic and occult infections were born in Eastern Europe, Africa, or Asia (451/544, 83% and 14/24, 58%); acute infections were largely seen in UK-born donors (19/28, 68%). Genotyping of 266 HBV-positive samples revealed five genotypes (A-E), reflecting ethnicity and country of birth. Most OBIs were identified in repeat donors (19/25); lookback data identified a transmission rate of 8.3%. It is estimated that at least 13 potentially infectious donations from donors with OBI remain undetected annually, equating to an overall residual transmission risk of 3.1 per million donations using our current screening strategy of HBsAg screening with HBV nucleic acid testing (NAT) in pools of 24.

CONCLUSIONS

OBI accounted for the majority of the HBV residual risk in England. Further cost-benefit analysis is required to estimate if our current HBV screening strategy should be changed.

Blood Transfusion-Associated Infections in the Twenty-First Century: New Challenges

Blood transfusions are vital components of modern medical treatment to which there is no viable alternative despite efforts to create artificial blood. Each year thousands of lives are saved by blood transfusions in every country of the world. However, blood and blood products can result in significant adverse events including immunologic reactions, infections, inefficacy, and others which can sometimes result in death and severe disability. Thus, the sustainability of safe blood systems and costs are considered to be at crisis level. In industrialized countries, the risk of transfusion-transmitted infections such as HIV, syphilis, hepatitis viruses B and C are very low [generally [<1 in a million units], but in developing countries [especially in Africa] blood safety is still not assured. Compounding the problem of blood/product safety with respect to infectious agents are new emerging infectious microbes that are not being routinely tested for in blood that are donated. This chapter reviews the infectious risk of blood transfusions, types, mode and geographic variation, and the methods being used by blood services to attenuate and prevent these risks.

The current incidence, prevalence, and residual risk of hepatitis B viral infections among voluntary blood donors in China

BACKGROUND

There are few data available on the prevalence, incidence, and residual risk of transfusion-transmitted HBV (TT-HBV) infections among Chinese blood donors. This study investigated the demographic characteristics of blood donors, as well as the prevalence, incidence, and residual risk (RR) of TT-HBV infections in six large blood centers in different regions of China.

METHODS

The demographic characteristics and HBV screening test results of blood donors from six blood centers in different regions in China were collected and analyzed. The hepatitis B surface antigen (HBsAg) yield approach was used to estimate the incidence of HBV. Then, the RR of TT-HBV infections was evaluated using the incidence-window period model.

RESULTS

The majority of donors were between 18 and 35 years old (including 35), with the exception of the Changzhi Blood Center where a majority of donors were between 35 and 55 years old (including 55). The prevalences of HBV were 0.13%, 0.078%, 0.16%, 0.07%, 0.20%, 0.25% in Hefei, Dalian, Changzhi, Kaifeng, Mianyang and Fujian, respectively. The estimated corresponding incidences were 213.44, 161.59, 989.80, 278.05, 125.31 and 352.19 per 10⁵ person-years. Using an infectious window period of 59 days, the RR for HBV was estimated to be 34.14, 25.85, 158.35, 44.48, 20.04 and 56.35 per 10⁵ person-years in Hefei, Dalian, Changzhi, Kaifeng, Mianyang and Fujian, respectively.

CONCLUSION

Despite the introduction of more sensitive assays in blood screening, our data revealed that the current residual risk of TT-HBV infection was still high (overall 56.53 per 10⁵ py). A continuous monitoring of the residual risk of transfusion-transmitted infections is crucial for safe blood management.

Molecular and serological detection of occult hepatitis B virus among healthy hepatitis B surface antigen-negative blood donors in Malaysia

BACKGROUND

Occult hepatitis B infections are becoming a major global threat, but the available data on its prevalence in various parts of the world are often divergent.

OBJECTIVE

This study aimed to detect occult hepatitis B virus in hepatitis B surface antigen-negative serum using anti-HBc as a marker of previous infection.

PATIENT AND METHODS

A total of 1000 randomly selected hepatitis B surface antigen-negative sera from blood donors were tested for hepatitis B core antibody and hepatitis B surface antibody using an ELISA and nested polymerase chain reaction was done using primers specific to the surface gene (S-gene).

RESULTS

Of the 1000 samples 55 (5.5%) were found to be reactive, of which 87.3% (48/55) were positive for hepatitis B surface antibody, indicating immunity as a result of previous infection however, that does not exclude active infection with escaped mutant HBV. Nested PCR results showed the presence of hepatitis B viral DNA in all the 55 samples that were positive for core protein, which is in agreement with the hepatitis B surface antibody result.

CONCLUSION

This study reveals the 5.5% prevalence of occult hepatitis B among Malaysian blood donors as well as the reliability of using hepatitis B core antibody in screening for occult hepatitis B infection in low endemic, low socioeconomic settings.

Refining the risk estimate for transfusion-transmission of occult hepatitis B virus

BACKGROUND AND OBJECTIVES

We previously published a model to estimate the residual risk (RR) for occult hepatitis B infection (OBI) in the absence of universal anti-HBc testing. To incorporate new information on the epidemiology of OBI, we describe model refinements and estimate a more accurate HBV RR due to OBI in Australia.

MATERIALS AND METHODS

In our original model, the OBI risk, p(OBI), was defined by the rate of 'non-detection' by the HBV DNA screening test in use, p(NAT non-detection), and the average infectivity of blood components from OBI donors, p(transmission). We revised the model by integrating three refinements: that donations with anti-HBs levels of >10 IU/l, or donations solely for manufactured plasma products, be excluded from the risk calculation, and an updated estimate of p(transmission).

RESULTS

Refining our OBI RR model resulted in a more than 10-fold reduction in the reported RR risk to recipients from OBI in our donor population. Based on the use of a common data set, the mean OBI RR risk decreased from 1 in 374 354 donations (95% CI: 1 in 191 940-1 072 681) to 1 in 3 984 033 (95% CI: 1 in 1 146 188-65 268 257) for the refined model.

CONCLUSION

Our model refinements provide a more realistic measure of the HBV RR in the donor population. Unlike the previous model, the new model demonstrates that the risk of HBV due to OBI in the Australian blood donor population is negligible, and further potentially cost-ineffective risk management strategies are not currently warranted.

Current concepts in the prevention of pathogen transmission via blood/plasma-derived products for bleeding disorders

The pathogen safety of blood/plasma-derived products has historically been a subject of significant concern to the medical community. Measures such as donor selection and blood screening have contributed to increase the safety of these products, but pathogen transmission does still occur. Reasons for this include lack of sensitivity/specificity of current screening methods, lack of reliable screening tests for some pathogens (e.g. prions) and the fact that many potentially harmful infectious agents are not routinely screened for. Methods for the purification/inactivation of blood/plasma-derived products have been developed in order to further reduce the residual risk, but low concentrations of pathogens do not necessarily imply a low level of risk for the patient and so the overall challenge of minimising risk remains. This review aims to discuss the variable level of pathogenic risk and describes the current screening methods used to prevent/detect the presence of pathogens in blood/plasma-derived products.

The yield of universal antibody to hepatitis B core antigen donor screening in the Netherlands, a hepatitis B virus low-endemic country

BACKGROUND

In the Netherlands, universal antibody to hepatitis B core antigen (anti-HBc) donor screening was introduced in July 2011 to intercept potentially infectious donations slipping through hepatitis B surface antigen (HBsAg) and hepatitis B virus (HBV) DNA minipool screening (HBV DNA MP6).

STUDY DESIGN AND METHODS

The yield and donor loss were evaluated after the first 2 years of universal anti-HBc donor screening. A total of 382,173 donors were tested for anti-HBc and, if positive, for antibody to HBsAg (anti-HBs). Anti-HBc-reactive donors with anti-HBs of less than 200 IU/L were deferred, but repeat donors were allowed retesting after 6 months if anti-HBs was less than 10 IU/mL. Anti-HBc false positivity was estimated using the crude anti-HBc signal, family name-based ethnicity scoring, and donor follow-up.

RESULTS

Anti-HBc screening identified 13 confirmed or potential HBsAg- and HBV DNA MP6-negative recent HBV infections. In addition, 820 anti-HBc-reactive donors with low anti-HBs titers (<200 IU/mL), potentially harboring occult HBV infection (OBI), were identified and deferred. Overall, 1583 (0.41%) donors were deferred: 1178 (0.31%) during first-time anti-HBc screening, 361 (0.09%) anti-HBc seroconverters, and 44 (0.01%) donors with waning anti-HBs titers. Only 188 of 1583 (12%) deferred donors could be reentered upon retesting. Estimated anti-HBc false positivity was 16%, but varied greatly among anti-HBc-reactive donors with and without anti-HBs (8% vs. 62%).

CONCLUSION

Anti-HBc testing has improved the safety of the Dutch blood supply but its exact yield remains difficult to determine, due to the complexity of confirming anti-HBc reactivity and OBI. In a low-endemic country, donor loss associated with anti-HBc screening is sustainable, but adds to the already considerable list of donor exclusions.

The use of rapid diagnostic tests for transfusion infectious screening in Africa: a literature review

Infectious risk associated with blood transfusion remains a major public health challenge in Africa, where prevalence rates of the major transfusion-transmissible infections (ie, hepatitis B, hepatitis C, human immunodeficiency virus, and syphilis) are among the highest in the world. Resource-limited blood services often operate with minimal predonation screening safeguards, prompting exclusive reliance on laboratory testing to mitigate infectious risk. Transfusion screening with rapid diagnostic tests (RDTs) has been adopted in areas that lack the capacity to support the routine use of more sophisticated technologies. However, uncertainty surrounding the performance of some RDTs in the field has spurred debate regarding their application to blood donation screening. Our review of the literature identified 17 studies that evaluated RDTs for the infectious screening of blood donors in Africa. The review highlights the variable performance of available RDTs and the importance of their use in a quality-assured manner. Deficiencies in performance observed with some RDTs underscore the need to validate test kits prior to use under field conditions with locally acquired samples. Suboptimal sensitivities of some available tests, specifically hepatitis B virus rapid assays, question their suitability in single-test algorithms, particularly in high-prevalence regions. Although RDTs have limitations, many of which can be addressed through improved training and quality systems, they are frequently the only viable option for infectious screening in resource-poor African countries. Therefore, additional studies and specific guidelines regarding the use of RDTs in the context of blood safety are needed.

Defining acceptable epidemiology ranges in donor populations based on the contamination risk of finished plasma-derived products

BACKGROUND

For a given plasma-derived product, the risk of final product contamination by hepatitis B virus, hepatitis C virus and human immunodeficiency virus depends upon the epidemiology in the donor population, the virus load in a donation, the product yield and the effective virus reduction capacity in manufacturing.

STUDY DESIGN AND METHODS

A Monte Carlo simulation model was developed to estimate the risk of virus contamination of a final product resulting from virus contamination of plasma pools for fractionation. The model was run for both source and recovered plasma at various incidence rates for the three viruses to determine virus loads in minipools and fractionation pools resulting from donations with virus levels below test sensitivities. Together with the virus reduction capacity and yield of a theoretical worst case plasma-derived product, the contamination risk in a final vial was calculated.

RESULTS

Acceptable upper-bound centre-level incidence rates in the donor population (per donor centre) result in final products with very high margins of virus safety; the largest determinant of these 'Process Limits' is the virus reduction capacity of the manufacturing process. Short donation intervals and long inventory hold periods for source plasma compensates the lower incidence rates typically observed in recovered plasma donors.

CONCLUSIONS

The model calculates process limits for epidemiological data at collection centres based on an appropriate margin of virus safety for final products. The model also takes into consideration the impact of different donor/donation management systems for source and recovered plasma on the number of low viraemic donations entering the plasma pool for fractionation.

A mathematical approach to estimate the efficacy of individual-donation and minipool nucleic acid amplification test options in preventing transmission risk by window period and occult hepatitis B virus infections

BACKGROUND

Sensitivity data from a head-to-head comparison study in South Africa were used to compare the efficacy of the Ultrio Plus assay in individual-donation (ID) and minipool (MP)4 and MP8 formats with that of TaqScreen MP6 in preventing hepatitis B virus (HBV) transmission risk.

STUDY DESIGN AND METHODS

The replicate nucleic acid test (NAT) results on 106 HBV NAT (Ultrio)-yield samples and 29 HBV DNA (Ultrio)-negative, hepatitis B surface antigen (HBsAg)-positive samples were used to determine the viral load in copies/mL against the Eurohep HBV standard by probit analysis. Random viral load distributions were established in 32 pre-HBsAg window period (WP), 15 post-HBsAg WP, and 56 occult HBV infection (OBI) donations. Regression analysis of log viral load and Poisson distribution statistics of infectious HBV particles in blood components was used to predict infectivity and efficacy of NAT options in removing HBV transmission risk.

RESULTS

For red blood cell transfusions (20 mL of plasma), the modeling predicted an Ultrio Plus ID-NAT efficacy of 68 and 83% in removing WP and (antibody to hepatitis B surface antigen-negative) OBI transmission risk, respectively, compared to 52 and 49% by TaqScreen MP6. For 200 mL of fresh-frozen plasma the estimated efficacy levels by these ID- and MP6-NAT options reduced to 57 and 44% for WP and to 67 and 34% for OBI donations, respectively.

CONCLUSION

The efficacy of the currently available commercial NAT systems in reducing HBV transmission risk is mainly driven by the pool size and the transfusion plasma volume. The modeled OBI transmission risk and NAT efficacy levels were in line with those recently reported in three lookback studies and give more insight in the incremental safety provided by HBsAg and antibody to hepatitis B core antigen testing of ID-NAT screened blood.

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.