New insights into the natural history of hepatitis E virus infection through a longitudinal study of multitransfused immunocompetent patients in France.

Little is known about the natural history of Hepatitis E virus (HEV) infection in immunocompetent individuals. The prevalence, the course of infection and the occurrence of transmission by transfusion were investigated in multitransfused immunocompetent patients/blood donor pairs included in a longitudinal sample repository collection and followed up between 1988 and 2010. Ninety-eight subjects aged 6-89 years and suffering from acquired haemoglobinopathies were tested for HEV markers (IgM, IgG and RNA) in serial samples collected every 2 or 3 years. Eighteen patients (18.4%) were positive for HEV-IgG at baseline with a prevalence increasing from 12.5% below 26 years to 32% above 56 years. Nine patients remained IgG positive along the study and nine lost their antibodies after a mean follow-up of 7.4 years (1-22 years). One seropositive patient showed an increase of IgG level and RNA-HEV reappearance 1 year after inclusion, suggesting a reinfection and one seroconversion, probably acquired through blood transfusion was observed. This first longitudinal study including immunocompetent individuals confirms that HEV infection is common in Western Europe and that transfusion transmission occurs probably less frequently than expected. In addition, seroreversion and reinfection seem to be common. This suggests that the anti-HEV may not persist overtime naturally. However, repeat exposure to the virus related to the high prevalence of HEV infection may result in a sustainable specific IgG response.

Screening for transfusion transmissible infections using rapid diagnostic tests in Africa: a potential hazard to blood safety?

Rapid diagnostic tests (RDTs) are routinely used in African blood centres. We analysed data from two cross-sectional studies representing 95 blood centres in 29 African countries. Standardized panels of sera containing varying concentrations of anti-human immunodeficiency virus (HIV) antibodies (Ab), hepatitis B virus antigen (HBsAg) and antihepatitis C virus (HCV) Ab were screened using routine operational testing procedures at the centres. Sensitivity of detection using RDTs was high for HIV Ab-positive samples, but low for intermediately HBsAg (51·5%) and HCV Ab (40·6%)-positive samples. These findings suggest that current RDT use in Africa could pose a hazard to blood safety.

Correlation between the promoter basal core and precore mutations and HBsAg quantification in French blood donors infected with hepatitis B virus.

Hepatitis B virus (HBV) basal core promoter (BCP) and precore (PC) mutations, HBV viral load and HBV surface antigen (HBsAg) quantitation were screened to assess correlations between these HBV markers in asymptomatic chronic hepatitis B carriers in France. From January 2006 to July 2007, 200 sera were collected from patients who were discovered to be HBsAg-positive when they volunteered to give blood. Direct sequencing of precore/core gene was used to detect A1762T/G1764A mutations in the BCP and G1896A in the PC region. HBV viral load and HBsAg were quantified with two commercials assays. The prevalence of the BCP and PC mixed/mutants were 37% and 60% respectively (P = 0.0001). HBV DNA level and HBsAg titer were significantly lower in subjects harboring the mixed/mutant PC virus compared to those infected by the wild phenotype. No significant difference was observed in HBV viral loads of blood donors infected by wild or mixed/mutant BCP viruses. Mutant or mixed PC virus was associated with male gender, HBeAb-positive status and HBV/D and HBV/E genotypes. BCP mutations were associated with age, and both HBV/A-HBV/E genotypes.The genetic properties of HBV in this cohort showed that most of the blood donors had a negative HBeAg serological status and harbored the PC mutant phenotype in combination with low levels of both HBV DNA and HBsAg. As the study was conducted in healthy subjects who could be considered as asmptomatic carriers, these results suggest a possible protective effect of the G1896A mutation against severe liver lesions.

A pilot external quality assurance study of transfusion screening for HIV, HCV and HBsAG in 12 African countries.

BACKGROUND AND OBJECTIVES: Serologic screening for the major transfusion transmissible viruses (TTV) is critical to blood safety and has been widely implemented. However, actual performance as measured by proficiency testing has not been well studied in sub-Saharan Africa. Therefore, we conducted an external quality assessment of laboratories engaged in transfusion screening in the region. MATERIALS AND METHODS: Blinded test panels, each comprising 25 serum samples that were pedigreed for HIV, HBsAg, HCV and negative status, were sent to participating laboratories. The panels were tested using the laboratories' routine donor screening methods and conditions. Sensitivity and specificity were calculated, and multivariable analysis was used to compare performance against mode of testing, country and infrastructure. RESULTS: A total of 12 African countries and 44 laboratories participated in the study. The mean (range) sensitivities for HIV, HBsAg and HCV were 91·9% (14·3-100), 86·7% (42·9-100) and 90·1% (50-100), respectively. Mean specificities for HIV, HBsAg and HCV were 97·7%, 97% and 99·5%, respectively. After adjusting for country and infrastructure, rapid tests had significantly lower sensitivity than enzyme immunoassays for both HBsAg (P < 0·0001) and HCV (P < 0·05). Sensitivity also varied by country and selected infrastructure variables. CONCLUSION: While specificity was high, sensitivity was more variable and deficient in a substantial number of testing laboratories. These findings underscore the importance of proficiency testing and quality control, particularly in Africa where TTV prevalence is high.

Comparative evaluation of the Geenius HCV supplemental assay and Inno-LIA HCV score assay in detecting anti-HCV antibodies.

OBJECTIVE: This study compared two assays aimed at confirming the presence of anti-HCV antibodies (Ab) after a positive screening: Geenius HCV supplemental assay (Bio-Rad, Marne la Coquette, France) and the Inno-LIA HCV score assay (Fujirebio, Les Ulis, France). MATERIAL AND METHODS: A total of 180 archived samples were investigated including 119 samples collected at different stages of HCV infection in 25 hemodialyzed patients who underwent HCV seroconversion, 14 samples from 4 commercial seroconversion panels, 47 Ab positive/HCV-RNA positive blood donations of which 7 showing an single reactivity in confirmatory assays. Samples were investigated and results were interpreted with the two assays according to the manufacturers' instructions. RESULTS: Overall, Geenius and Inno-LIA were concordant for 84% (151/180) samples: 38 negative, 17 indeterminate and 96 positive. Of the 29 discrepant results, 26 were overclassified with Inno-LIA. HCV seroconversion was detected with Inno-LIA 4 and 7 days prior to Geenius in two panels. The high positive rate observed with Inno-LIA (64%) compared to Geenius (54%) was mainly due to low reactivities considered positive according to interpretation criteria, which could affect specificity. CONCLUSION: Although HCV supplemental assays are not recommended for the diagnostic of HCV infection, which is primarily based on HCV-RNA testing, both assays are suitable as second line anti-HCV tests when Ab screening is positive and RNA testing cannot be performed. Moreover, Geenius system provides an objective result in less than 30minutes, which is compatible when a rapid diagnostic is required.

High levels of serum hepatitis B virus DNA in patients with 'anti-HBc alone': role of HBsAg mutants.

It remains unclear how the detection of hepatitis B core antibody (anti-HBc) in the absence of hepatitis B surface antigen (HBsAg) and antibody (anti-HBs) should be interpreted and whether all patients with this pattern need to be tested for hepatitis B virus (HBV)-DNA. This study aimed at reassessing the significance of 'anti-HBc alone' in unselected sera referred to the clinical laboratory and determining whether significant HBV viraemia can be found in this setting. Of the 6431 patients tested for HBsAg, total anti-HBc and anti-HBs in a Paris hospital over a 1-year period, 362 (5.6%) had 'anti-HBc alone' (24.8% of anti-HBc-positive patients). Only 11 of the 362 sera (3.0%) were found to be false positive. One patient was in the resolving phase of acute hepatitis B. HBV-DNA was detected in 10 of 362 (2.8%) patients, using a commercial standardized assay (threshold: 350 IU/mL). Viral loads exceeded 10(4) copies/mL in 6 of 10 patients. Mutations in the HBsAg immunodominant region were identified in seven of the viraemic patients. HBsAg was detected in only two cases when retested by one of the latest, multivalent assays. Neither human immunodeficiency virus nor hepatitis C virus serostatus distinguished between patients with and without HBV-DNA. In conclusion, 'anti-HBc alone' should be considered a risk marker for a so-called 'false occult' HBV infection with significant viraemia. Indeed, results in this hospital population indicate that a small proportion of patients with 'anti-HBc alone' have high viral loads, revealing the occurrence of infection with HBV mutants that escape detection even by multivalent HBsAg assays.

[Results of a novel real-time PCR, sequence analysis, Inno-LiPA line probe assays in the detection of hepatitis B virus G1896A precore mutation in French blood donors]. / Résultats de trois méthodes pour la détection de la mutation précore G1896A du virus de l'hépatite B chez les donneurs de sang français : PCR temps réel, séquençage et test Inno-LIPA.

AIM: To screen hepatitis B virus (HBV) genotypes and associated basal core promoter (BCP; T1762A/A1764) and precore (PC; A1896) mutations among the 100 HBV surface antigen (HBsAg) positive voluntary blood donors in France. METHODS: HBV genotypes were determined by using direct sequence analysis. Three methods were used to detect G1896A mutation: non-commercial real-time PCR (PCRTR°, line probe assay (InnoLiPA HBV PreCore, INNOGENETICS(®)) and direct sequencing of precore gene. HBV viral load was quantified with two commercial real-time PCR (COBAS(®) AmpliPrep/COBAS(®) TaqMan(®) HBV Test/Roche and Real Time HBV/M2000/Abbott). RESULTS: The mean age of donors was 30 (18-64). Patients were from Africa (42%), Europa (50%), and Asia (8%). HBV/D was the most predominant (37%) genotype followed by HBV/A (31%) and HBV/E (22%). PC and BCP mutants were found in 57% with Inno-LIPA HBV test and 59% with both PCRTR and sequencing methods. A significant difference in the viral load of blood donors with wild and PC mutants was observed with the Taqman Cobas real time PCR (3,19 Log(10) UI/ml versus 4,93 Log(10) UI/ml, p < 0.05). Precore phenotype determination was in agreement with the three PC mutation detection methods in 56% of cases. CONCLUSIONS: Non-Caucasian genotype E was present in the French blood donors. PC mutation was more common than BCP mutations in this study. As HBV infected blood donors were more often asymptomatic carriers, we could speculate that the G1896A mutation may favour the asymptomatic state, supporting previous observations.

Challenges in transfusion-transmitted infection screening in Sub-Saharan Africa.

In Sub-Saharan Africa, high clinical demand for transfusion faces endemic bloodborne infections and limited resources. Blood screening for transfusion-transmitted bloodborne pathogens is the cornerstone of blood safety. Although there have been substantial improvements over the years, challenges in transfusion-transmitted infection screening that have been identified repeatedly long ago still need to be addressed. Affordability and sustainability of state-of-the-art quality assessed serological and molecular assays, and associated confirmation strategies remain of real concern. In addition, limited resources and infrastructures hamper the development of adequate facilities, quality management, and staff qualification, and exacerbate shortage of reagents and equipment maintenance. It is also important to maintain effort in constituting pools of repeat voluntary non-remunerated donors. Alternative strategies for blood screening that take into account local circumstances might be desirable but they should rely on appropriate field evaluation and careful economic assessment rather than dogma established from high-resource settings.

[Gestion of arboviral alerts: Experience feedback from the Secproch working group of the French "Haut Conseil de la santé publique" (2019-2021)]. / Gestion des alertes arbovirales : retour d'expérience du groupe de travail Secproch du Haut Conseil de la santé publique (2019­2021).

The Secproch working group (for "sécurité des produits issus du corps humain") was created in 2019 within the « Haut Conseil de la santé publique ¼ (HCSP) for addressing all the questions related to labile blood products, organs, tissues, cells (OTC) and gametes issued from human body. It is notably in charge of the management of alerts regarding arbovirus infections. These infections due to arthropod-transmitted viruses are responsible for emergence and reemergence, notably in the context of global warming. This review relates the alerts taken into consideration by the Secproch group between 2019 and 2021 following three pathologies due to Flaviviridae : dengue, West Nile virus (WNV) infection and tick-borne encephalitis (TBE). The dengue alerts have occurred in French Indies where the virus is endemic/epidemic, Reunion Island where the population was naïve until 2018 towards the virus, and the metropole where foci of autochthonous cases are observed sporadically. The WNV infection was responsible of both human and equine cases in 2019 in the South of France but with intensity much less than in 2018. At last, the TBE virus was at the origin of a cluster of about 40 cases in the Ain department following a contamination by crude non-pasteurized goat cheese. This review offers the opportunity to reevaluate the risks linked to these three viruses through blood products and organs/tissues/cells and to precise the means recommended by HCSP to secure these products.

Building capacities in research for blood services in Africa.

BACKGROUND: Capacity building of African based blood services researchers has been identified as key in developing a sustainable programme of generation local evidence to support sound decision making. There are a number of research training programmes that have been instituted targeted at blood services in Africa. The article shares programme experiences of building research capacities for blood services in Africa. METHODOLOGY: The Francophone Africa Transfusion Medicine Research Training network, the NIH REDS-III and NIH Fogarty South Africa programmes and T-REC (Building transfusion research capacity in Africa) have been the key research capacity programmes targeting blood services in Africa over the last decade. To understand their experiences on the implementation of the capacity building programmes, data were drawn from research outputs, publications and end of programme reports. The success, challenges and the main research outputs from their initiatives were highlighted. RESULTS: The Francophone research network achievements included more than 135 trainees and in excess of 30 publications. The NIH REDS study the achievements included more than 12 research publications with South Africa junior investigators as lead authors. The NIH Fogarty program currently includes 56 short course trainees, 5 Masters and 6 PhD candidates. The four year (2011-2015, funding period) T-REC programme produced more than 20 publications, 4 PhDs, 42 in-service Diploma in Project Design and Management (DPDM), and supported bursaries for 60 Masters/undergraduate research. The main common challenges in the running of the research programmes include shortages of in-country mentoring and identified needs in high quality research grants writing. DISCUSSION AND CONCLUSION: The key achievements for the blood services research capacity building include a mix of short courses, medium-term (epidemiology & biostats) and MS/PhD degree training. Also, having a "train the trainers' programme to develop in-country mentors has been instrumental. Overall, the key recommendations for blood services research capacity building include the need for research collaborations with high-income countries which can jump-start research,and for more in-country grant-writing capacity building, which would help sustainability.

Impact on blood safety of the last arboviruses outbreaks in French Polynesia (2012-2018).

BACKGROUND: Several successive arbovirus outbreaks have affected French Polynesia (FP) in the recent past years due to different dengue serotypes (DENV) present for several decades, Zika (ZIKV) (2013-2014) and chikungunya (CHIKV) (2014-2015) viruses with a potential impact on blood safety and blood supply due to the geographical isolation of these islands. This study reports an assessment of the impact of these outbreaks on blood products supply and infectious safety in FP and discuss the effectiveness of implemented preventive measures. METHODS: To ensure the infectious safety of blood products during outbreaks, several measures have successively been introduced as the selection of donors suspected of infection, the nucleic acid testing (NAT) and the pathogen reduction of platelets and plasmas. RESULTS: The donor deferral rate increased by 6% between 2012 and 2014 without changes in the number of collected donations. NAT excluded five blood donations reactive for DENV RNA, 42 for ZIKV and 34 for CHIKV. As Zika screening could not been implemented before the third month of the outbreak, 36 blood products from ZIKV-infected donors were transfused to 26 recipients. However, no transfusion-transmitted arbovirus has been reported. CONCLUSION: The last past arboviruses outbreaks did not have a significant impact on blood supply in FP. The measures introduced to prevent arbovirus transmission by transfusion were able to maintain infectious safety for all blood products without impairing self-sufficiency.

Blood safety strategies for human T-cell lymphotropic virus in Europe.

BACKGROUND: To prevent the blood transmission of human T-cell lymphotropic virus (HTLV), different countries have introduced anti-HTLV blood screening. Furthermore, leucoreduction of blood components has been implemented to preclude the transmission of infectious agents present in white blood cells. STUDY DESIGN AND METHODS: To evaluate the current European strategies adopted to ensure the blood safety for HTLV, a European investigation spanning a period from 2003 to 2008 was carried out. RESULTS: In 2003, of the 23 included countries, 11 performed anti-HTLV screening, four of which (Scandinavian countries) only did it on first-time donors. Norway and Finland stopped it in 2007 and 2008, respectively. Two groups may be defined according to increasing prevalence rates per 10 000 donations in first-time donors: Scandinavia and Ireland (0 to 0.17), France, the Netherlands and UK (0.45 to 0.48); Romania was clearly apart from all other participating countries (5.33). HTLV-positive donors (88.6%) either come from endemic areas (82.3%) or declare to have a sexual partner coming from endemic areas (6.3%). Of the 283 HTLV-positive donations that could be characterized, 6.6% were HTLV-II. Fourteen of 22 countries currently use systematic leucoreduction, at least in cellular blood components. Six countries perform both universal anti-HTLV screening and blood cell leucoreduction. CONCLUSION: The implementation of leucoreduction did not modify the blood HTLVscreening policy, except for Norway and Finland. Several screening strategies in low endemic countries performing leucoreduction were discussed. However, the withdrawal of anti-HTLV screening should be decided after assessing the remaining HTLV transfusion risk.

[Quantitative estimate of the risk of blood donation contamination by infectious agents]. / Estimation quantitative du risque de contamination d'un don de sang par des agents infectieux.

The occurrence of asymptomatic penetration of certain infectious agents in blood presents a risk of transmission of one of these agents during blood transfusion. Although well controlled for some infectious agents (HIV, HTLV, HCV, HBV), this risk is nevertheless neither documented nor quantified for other pathogens that are responsible for serologically unscreened or undetectable infections at the time of blood donation. This risk is generally low in endemic situations, although it increases for particular time periods and locations when clustered cases or outbreaks occur. Prevention measures may then be implemented (interruption of blood collection, quarantined donations, etc.). These measures can have an important impact, particularly by limiting the supply of blood products to health care facilities. It is therefore important for these measures to be adapted to the risk of transmission through blood transfusion. Quantitative risk estimates of blood donation contamination can therefore contribute to guiding those measures. In this context, in early 2005, the French Public Health Institute (InVS) started a project with the aim of obtaining a priori quantitative risk estimates of contamination of a blood donation by infectious agents for various scenarios in terms of incidence and time-space distribution. The objective of this article is to update the last estimates of residual risks of the major transfusion-transmitted viral infections (HIV, HTLV, HCV and HBV) and to present the work realized by the working group << Quantitative estimate of the risk of blood donation contamination by infectious agents>>.

Human pegivirus-1 (HPgV-1) RNA prevalence and genotypes in volunteer blood donors from the Brazilian Amazon.

OBJECTIVES: The objectives of this study were to evaluate the prevalence of Human Pegivirus-1 (HPgV-1) viremia and genotype diversity among healthy blood donors from the Eastern Brazilian Amazon (city of Macapá, State of Amapá). There is little information for prevalence and circulation of HPgV-1 in this remote Brazilian region. MATERIALS AND METHODS: We conducted a study evaluating the HPgV-1 RNA prevalence and circulating genotypes in 431 volunteer blood donors originating from the Eastern Brazilian Amazon. The obtained HPgV-1 positive samples were submitted to sequencing and genotyping analysis in order to examine the genotype diversity of this virus in the Brazilian Amazon. RESULTS: Our results demonstrated a prevalence of HPgV-1 RNA in 9.5% of the tested blood donors. The phylogenetic analyses of the detected positive samples showed the presence of HPgV-1 genotypes 1, 2 and 3. The most frequently detected genotype was 2 (78.0% of the cases) represented by sub-genotypes 2A (39.0%) and 2B (39.0%). At lower rates, genotypes 1 (14.6%) and 3 (7.4%) were also detected. CONCLUSION: Our results revealed the presence of genotypes with European, Asiatic and African endemicity in Amazonian blood donors, probably due to the complex miscegenation processes that took place in this Brazilian region. More investigations, including information for the prevalence of HPgV-1 RNA in blood donors from other Latin American countries are needed to estimate the viremic rates and genotype distribution of this virus in a highly diverse continent like South America.

Hepatitis G virus: a suitable marker of in vivo efficacy for pathogen inactivation.

Being an orphan virus despite a large number of investigations, hepatitis G virus is a blood-borne agent for which screening is not required in blood donations. The in vivo efficacy of pathogen inactivation methods could be assessed by the absence of hepatitis G virus markers after transfusion of pathogen-inactivated blood products, in recipients susceptible to infection before the transfusion.

[Genetic diversity of human erythroviruses: consequences on infectious safety of blood products and plasma derivatives]. / Conséquences de la diversité génétique des érythrovirus humains sur la sécurité infectieuse des produits sanguins labiles et des médicaments dérivés du sang.

Sequence analysis of human erythroviruses shows an organization into three genotypes; genotype 1 with B19 Parvovirus (B19 V) and 2 new genotypes with a genetic diversity markedly distinct from that of B19 V. The frequency of each genotype depends on geographic origin and population. Human erythroviruses infection can be transmitted by transfusion. In immunocompetent recipients, B19 V exposure is generally inconsequential, since a large proportion is immunized. However, such a contamination may have severe clinical outcome in not immunized patients with shortened red cell survival, in seronegative pregnant women and in immunocompromised patients. No prevention of blood transmission is currently performed, but a preventive strategy could be discussed for at-risk recipients. In plasma derivatives, B19VDNA screening is done with a threshold of 104 IU/mL. With recent data of a new classification on the human erythroviruses genotypes, DNA testing assays would be validated in accordance with genetic variability, in order to guarantee optimal safety.

Transfusion-associated hazards: A revisit of their presentation.

As a therapy or a support to other therapies, despite being largely beneficial to patients in general, transfusion it is not devoid of some risks. In a moderate number of cases, patients may manifest adverse reactions, otherwise referred to as transfusion-associated hazards (TAHs). The latest French 2016 haemovigilance report indicates that 93% of TAHs are minor (grade 1), 5.5% are moderate (grade 2) and 1.6% are severe (grade 3), with only five deaths (grade 4) being attributed to transfusion with relative certainty (imputability of level [or grade] 1 to 3). Health-care providers need to be well aware of the benefits and potential risks (to best evaluate and discuss the benefit-risk ratio), how to prevent TAHs, the overall costs and the availability of alternative therapeutic options. In high-income countries, most blood establishments (BEs) and hospital blood banks (HBBs) have developed tools for reporting and analysing at least severe transfusion reactions. With nearly two decades of haemovigilance, transfusion reaction databases should be quite informative, though there are four main caveats that prevent it from being fully efficient: (ai) reporting is mainly declarative and is thus barely exhaustive even in countries where it is mandatory by law; (aii) it is often difficult to differentiate between the different complications related to transfusion, diseases, comorbidities and other types of therapies in patients suffering from debilitating conditions; (aiii) there is a lack of consistency in the definitions used to describe and report some transfusion reactions, their severity and their likelihood of being related to transfusion; and (aiv) it is difficult to assess the imputability of a particular BC given to a patient who has previously received many BCs over a relatively short period of time. When compiling all available information published so far, it appears that TAHs can be analysed using different approaches: (bi) their pathophysiological nature; (bii) their severity; (biii) the onset scheme; (biv) a quality assessment (preventable or non-preventable); (bv) their impact on ongoing therapy. Moreover, TAHs can be reported either in a non-integrative or in an integrative way; in the latter case, presentation may also differ when issued by a blood establishment or a treating ward. At some point, a recapitulative document would be useful to gain a better understanding of TAHs in order to decrease their occurrence and severity and allow decision makers to determine action plans: this is what this review attempts to make. This review attempts to merge the different aspects, with a focus on the hospital side, i.e., how the most frequent TAHs can be avoided or mitigated.

Measures to prevent transfusion-associated protozoal infections in non-endemic countries.

To understand the risk of protozoa transmission by blood is critical as: (i) the world has become globalized with extensive travel, and increased immigration; (ii) blood-borne protozoa is common in inter-Tropical areas; (iii) protozoa develop biological means to escape hosts' immune systems, together with complicated detection, surveillance, and biological testing; and (iv) life threatening-parasites are inadequately controlled by treatment or prevention. This question is relevant in France, with it's non-continental territories, such as French Guiana, located in the Amazon Basin, which is endemic for various Plasmodium ssp. responsible for malaria, and for Trypanosoma cruzi, which is responsible for Chagas disease. In France, specific questioning of blood donors is haphazard despite the increase in population migration over the last three decades: specific questioning must be emphasized and 'at-risk' donors should be identified and subsequently excluded from donation. Donor exclusion alone would only be partially efficient, there is also a need for relevant biological testing of blood donations and in particular for T. cruzi through the CE-marked test to organize a coherent prevention policy: precise studies would thus define which blood donations are subjected to this additional qualifying test when available.

[Diversity of hepatitis B virus and its consequences]. / Impact clinique, thérapeutique et diagnostique de la diversité génétique du virus de l'hépatite B.

The genetic diversity of hepatitis B virus (HBV) was defined on the basis of the characterisation of the major determinants in the antigenic loop of HBs antigen (Ag). Historically, nine subtypes were defined. Recently, based on sequence analysis, HBV genomes have been classified into eight genotypes (A-H) which present distinct geographical distributions. Genetic mutants may have a selective advantage in patients treated with passive or active immunization (hepatitis B immune globulin or vaccine). Anti-viral treatment can be responsible for the emergence of escape mutants with resistant mutations in the polymerase gene. These substitutions can lead to changes on HBsAg structure. The lack of detection of several envelope mutant viruses by some commercial HBsAg assays has been demonstrated. Substitutions involving precore/core region have also been found to prevent HBeAg synthesis.

Occult hepatitis B infection and transfusion-transmission risk.

Advances in serology and viral nucleic acid testing (NAT) over the last decades significantly reduced the risk of transfusion-transmitted hepatitis B virus (HBV). The combination of HBsAg testing and NAT efficiently prevents the majority of HBV transmission. However, a specific residual risk remains associated with extremely low viral DNA levels in blood donors with occult HBV infection (OBI) that are intermittently or not detectable even by highly sensitive individual donation (ID) NAT. Studies have reported HBV transfusion-transmission with blood components from donors with OBI that contained low amount of viruses (<200 virions). HBV transfusion-transmission seems to depend on a combination of several factors including the volume of plasma associated with the infected blood components transfused, the anti-HBV immune status of both recipient and donor, and possibly the viral fitness of the infecting HBV strain. Models based on clinical and experimental evidences estimate a residual transmission risk of 3-14% associated with OBI donations testing HBsAg and ID-NAT non-reactive. Anti-HBc testing has the potential to improve further blood safety but it may also compromise blood availability in settings with medium/high HBV prevalence. Pathogen reduction procedures might be considered.