唐山地区献血人群隐匿性乙型肝炎病毒感染分析

目的了解唐山地区无偿献血人群隐匿性乙型肝炎感染情况。方法用ELISA法检测无偿献血者的乙型肝炎血清标志物,对于HBsAg阴性样本,进行HBV核酸检测（NAT）,NAT阳性样本,用罗氏试剂确证HBV DNA载量。结果共检测116 741例血样,证实隐匿性乙型肝炎感染者35例,占总献血人数的0.29‰。其中97.1%隐匿性乙型肝炎感染者样本的HBV DNA滴度低于102IU/ml。在HBV DNA阳性人群中,抗-HBc阳性率较高,占81.5%,抗-HBs阳性或乙型肝炎病毒血清标志物全阴性也可检出HBV DNA分别占55.6%和22.9%。结论唐山地区献血人群中血清HBsAg阴性者存在一定比例的隐匿性HBV感染,其HBV病毒载量均较低,核酸检测能够提高HBV感染的检出率。     

Occult hepatitis B virus infection: implications in transfusion

Hepatitis B virus (HBV) presents a higher residual risk of transmission by transfusion than hepatitis C virus (HCV) or human immunodeficiency virus (HIV). While most infectious blood units are removed by screening for hepatitis B surface antigen (HBsAg), there is clear evidence that transmission by HBsAg-negative components occurs, in part, during the serologically negative window period, but more so during the late stages of infection. Donations negative for HBsAg, but positive for HBV DNA, with or without the presence of HBV antibodies, correspond to 'occult' HBV infection (OBI). The frequency of OBI depends on the relative sensitivity of both HBsAg and HBV DNA assays. It also depends on the prevalence of HBV infection in the population. OBI may follow recovery from infection, displaying antibody to hepatitis B surface antigen (anti-HBs) and persistent low-level viraemia, escape mutants undetected by the HBsAg assays, or healthy carriage with antibodies to hepatitis B e antigen (anti-HBe) and to hepatitis B core antigen (anti-HBc). Over time, in the latter situation, anti-HBe and, later, anti-HBc may become undetectable. The critical question is whether or not OBI is infectious by transfusion. All forms have been shown to be infectious in immunocompromised individuals, such as organ- or bone marrow-transplant recipients. In immunocompetent recipients, there is no evidence that anti-HBs-containing components (even at low titre) are infectious. Anti-HBc only, with HBV DNA, can be associated with infectivity, as can rare cases of HBV DNA without any serological HBV marker. If HBV nucleic acid amplification technology (NAT) is considered, the OBI viral load would usually be < 500 IU/ml, making testing of plasma pools unsuitable unless the sensitivity of NAT significantly increases by genome enrichment or test improvement.     

Sensitivity of individual donor nucleic acid testing (NAT) for the detection of hepatitis B infection by studying diluted NAT yield samples

BackgroundScreening blood donors for the presence of hepatitis B virus surface antigen (HBsAg) has been the backbone of blood safety. However, occult hepatitis B infection (OBI) in donors can be missed when only HBsAg screening is used. Nucleic acid testing (NAT) is capable of detecting OBI among donors. The aim of our study was to analyse the sensitivity of NAT for detecting OBI.ResultsOf the 18 samples studied, nine were NAT-reactive at a dilution of <1:4 and five out of these showed presence of antibody to core antigen (IgG+IgM). Antibody to surface antigen was present in only two of the nine NAT-reactive samples, one with antibody to core antigen and the other without. Six had a viral load in the range from <10 to 38 IU/mL whereas the viral load in the remaining three samples was not determined. Among the other nine samples which were NAT-reactive at dilutions ≥1:4, antibody to core antigen (IgG+IgM) was present in seven.DiscussionOur study showed that ID-NAT testing along with HBsAg screening could detect most potentially HBV infectious donors (including those with OBI). NAT screening for HBV on diluted samples could compromise blood safety because samples with a low viral load will escape detection.     

Post-transfusion occult hepatitis B (OBI): a global challenge for blood recipients and health authorities

Hepatitis B is one of the most frequent post-transfusion infections. Occult hepatitis B infection (OBI) is a form of hepatitis B infection in which, despite the presence of HBV-DNA in the serum and hepatocytes of the carrier, HBsAg is absent. In addition to the risk of transmission through the transfusion of infected blood, reactivation of hepatitis B in OBI patients and recipients of their blood can lead to cirrhosis, hepatic cancer, and reactivation of viral replication in the carrier. Therefore, effective assays to assess and screen for OBI in blood donors are of paramount importance and require urgent attention. Recently, several investigations in various regions of Iran have reported OBI in blood donors. In response, there has been a drive to apply more specific, sensitive, and accurate methods for the detection of HBV, which should become an obligatory screening process for all blood transfusion services. In this review, we address the progression of occult hepatitis B and the common problems associated with occult hepatitis B worldwide. Finally, we reflect on the research and screening that is being performed in Iran to deal with this problem.     

Incidence of hepatitis B virus infection in young Chinese blood donors born after mandatory implementation of neonatal hepatitis B vaccination nationwide

This study was carried out to determine the incidence of hepatitis B virus (HBV) infection in the young generation born after mandatory implementation of hepatitis B vaccination since 1992. Repeat blood donors born between 1992 and 1997 were enrolled, who gave blood at least twice during the past 3 years. Donors were tested for HBV infection markers of HBsAg, anti‐HBc, anti‐HBs and viral DNA by immunoassays (EIAs) and nucleic acid tests (NAT). A total of 14 937 pre‐donation screening qualified young repeat donors aged 18‐23 years were tested with 9 (0.06%) being HBsAg by EIA and 10 (1:1494) HBV DNA positive by Ultrio NAT (10.4 IU/mL), respectively. HBV DNA was further detected in 1:192 (9/1732) anti‐HBc+ repeat donors with Ultrio Plus NAT (3.4 IU/mL). Most cases were identified as occult HBV infection (OBI). Of 14 937 repeat donors, 20.9% were anti‐HBc+ positive, while approximately 50% of 12 024 repeat donors were anti‐HBs negative or had levels <100 IU/L. HBsAg+ or OBI strains were classified as wild type of genotype B or genotype C. Incident HBV infection in repeat donors was approximately 1:18.5 person‐years (1.1%/year) but significantly less frequent in donors with confirmed HBV vaccination (2.4%‐3.3%) than those unsure of vaccination status (10.5%; P = .0023). Hepatitis B virus vaccination appears largely protective of HBV infection, but incidence of infections increases in young adults with mostly undetectable or low anti‐HBs or occasionally high anti‐HBs. A boost of hepatitis B vaccine for adolescents prior to age 18 years may reduce HBV infection, and implementation of more sensitive NAT in blood donation screening may improve HBV safety in blood transfusion.     

Diagnostic strategy for occult hepatitis B virus infection

In 2008,the European Association for the study of the liver(EASL) defined occult hepatitis B virus infection (OBI) as thepresence of hepatitis B virus(HBV) DNA in the liver(with detectable or undetectable HBV DNA in the serum) of individuals testing hepatitis B surface antigen(HBsAg) negative by currently available assays.Several aspects of occult HBV infection are still poorly understood,including the definition itself and a standardized approach for laboratory-based detection,which is the purpose of this ...     

Occult Hepatitis B Virus Infection in Hemodialysis Patients: A Concept for Consideration

Hemodialysis patients potentially have an increased risk of infection with parenterally transmitted viral agents due to an impaired host immune response and multiple transfusion requirements. Viral hepatitis is considered as a problem for hemodialysis patients because 1.9% of all deaths among this population are related to the consequence of viral hepatitis. Hepatitis B virus (HBV) is one of the most important causes of transmitted infections by the parenteral route in hemodialysis patients. Occult HBV infection is characterized by presence of HBV infection without detectable hepatitis B surface antigen (HBsAg), which harbors potential risk of HBV transmission through hemodialysis. There are conflicting reports on the prevalence of occult HBV infection (OBI) in hemodialysis patients. Considering the importance of occult HBV infection in hemodialysis patients and the growing evidence on this subject, the purpose of this review is to provide comprehensive information on OBI prevalence in hemodialysis patients and highlight the most important points in this issue.     

Occult Hepatitis B: Clinical Implications and Treatment Decisions

First reported in 1978, occult hepatitis B is a term used to describe the presence of hepatitis B virus (HBV) DNA without hepatitis B surface antigenemia. The prevalence of occult HBV is unclear and depends in part on the sensitivity of the hepatitis B surface antigen (HBsAg) and DNA assays used as well as the prevalence of HBV infection in the study population. The origin of occult HBV also remains in question. Several mechanisms have been hypothesized including mutations in the regulatory regions of the HBV genome, persistence of Ig-bound HBV immune complexes, viral interference, and blockage of free HBsAg secretion. Occult HBV has important clinical implications such as transmission through blood transfusion, reactivation in the setting of immunosuppression, and interference with hepatitis C treatment. To date, there is little data pertaining to the treatment of occult HBV outside of the setting of chemotherapy-induced HBV reactivation.     

Update on occult hepatitis B virus infection

The event of mutations in the surface antigen gene of hepatitis B virus(HBV) results in undetectable hepatitis B surface antigen with positive/negative anti-hepatitis B core(anti-HBc) antibody status in serum and this phenomenon is named occult hepatitis B infection(OBI). The presence of anti-HBc antibody in serum is an important key for OBI tracking, although about 20% of OBI cases are negative for anti-HBc antibody. The diagnosis of OBI is mainly based on polymerase chain reaction(PCR) and real-time PCR assays. However, real-time PCR is a more reliable method than PCR. OBI is a great issue for the public health problem and a challenge for the clinical entity worldwide. The persistence of OBI may lead to the development of cirrhosis and hepatocellular carcinoma. With regard to OBI complications, the screening of HBV DNA by the highly sensitive molecular means should be implemented for:(1) patients with a previous history of chronic or acute HBV infection;(2) patients co-infected with hepatitis C virus/human immunodeficiency virus;(3) patients undergoing chemotherapy or anti-CD20 therapy;(4) recipients of organ transplant;(5) blood donors;(6) organ transplant donors;(7) thalassemia and hemophilia patients;(8) health care workers;(9) patients with liver related disease(cryptogenic);(10) hemodialysis patients;(11) patients undergoing lamivudine or interferon therapy; and(12) children in time of HBV vaccination especially in highly endemic areas of HBV. Active HBV vaccination should be implemented for the close relatives of patients who are negative for OBI markers. Thus, the goal of this review is to evaluate the rate of OBI with a focus on status of high risk groups in different regions of the world.     

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

Background The risk of post‐transfusion hepatitis B virus (HBV) infection has been reduced after the implementation of HBV nucleic acid amplification technology (NAT). However, the problem of HBV DNA‐positive and HBV surface antigen (HBsAg)‐negative occult HBV infections remains to be solved. This is in part due to the HBV DNA load being too low to detect these occult HBV infections using mini‐pool NAT. In Japan, the assay for the antibody against the HBV core antigen (anti‐HBc) has not completely excluded occult HBV infection. To solve this problem, we have developed a new method of concentrating HBV DNA and HBsAg simultaneously to increase the sensitivity of detection tests. Methods Virus concentration is achieved by the enhancement of the agglutination of viruses using poly‐L‐lysine in the presence of a bivalent metal. Poly‐L‐lysine‐coated magnetic beads are used to shorten the time of each step of the concentration procedure. Seventy‐seven anti‐HBc‐positive and HBsAg‐negative donations were examined. HBsAg and anti‐HBc were tested by enzyme immunoassay (EIA) (AxSYM; Abbott) and haemagglutination inhibition test (Japanese Red Cross), respectively. Results HBV surface antigen and HBV DNA levels were concentrated up to four‐ to sevenfold. Using this method, 35 of the 77 anti‐HBc‐positive and HBsAg‐negative donors were HBV DNA‐positive by individual NAT and a further five donors became HBV DNA‐positive by HBV concentration. Twenty‐seven of 40 occult HBV infections became HBsAg‐positive by HBsAg concentration. Conclusion Our new method of concentrating HBV and HBsAg increased the sensitivities of EIA and HBV NAT, and enabled us to detect 27 of 40 occult HBV infections by HBsAg EIA.     

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...     

重庆地区无偿献血人群隐匿性乙型肝炎病毒感染的特征

目的了解重庆地区无偿献血人群中隐匿性乙型肝炎病毒感染(occult hepatitis B virus infection,OBI)情况,分析其血清学和病毒学特征。方法应用酶联免疫法(筛查HBs Ag、抗-HCV、抗-HIV)及核酸检测(nucleic acid testing,NAT)法(筛查HBV、HCV、HIV)筛查重庆地区93 625份初筛合格的无偿献血者血液标本。对其中HBs Ag(-)但HBV DNA(﹢)的标本进行抗-HBs、抗-HBc、HBe Ag、抗-HBe 4项血清学标志物测定,进一步对抗-HBc(﹢)标本做病毒载量测定以及基因分型。结果 93 625份标本中HBs Ag(-)但HBV DNA(﹢)的检出率为0.097%(91/93 625)。91份阳性标本中79份为抗-HBc(﹢),检出率为0.084%(79/93 625)。该部分标本阳性者被视为OBI献血者。OBI献血者的血清学特征可以分为4种模式:单抗-HBc(﹢)、抗-HBc(﹢)/抗-HBs(﹢)、抗-HBc(﹢)/抗-HBe(﹢)以及抗-HBc(﹢)/抗-HBs(﹢)/抗-HBe(﹢)。病毒载量为0~1056.8IU/ml(中位数为108.6 IU/ml),基因型以B型为主。结论重庆地区无偿献血者中OBI检出率较高,其血清学和病毒学特征具有地区性。NAT能提高OBI检出的灵敏度,但也存在一定的假阳性,对血液安全具有重要影响。     

Occult hepatitis B virus infection

Occult hepatitis B virus(HBV)infection(OBI)refers to the presence of HBV DNA in the absence of detectable hepatitis B surface antigen.Since OBI was first described in the late 1970s,there has been increasing interest in this topic.The prevalence of OBI varies according to the different endemicity of HBV infection,cohort characteristics,and sensitivity and specificity of the methods used for detection.Although the exact mechanism of OBI has not been proved,intrahepatic persistence of viral covalently closed circular DNA under the host’s strong immune suppression of HBV replication and gene expression seems to be a cause.OBI has important clinical significance in several conditions.First,OBI can be transmitted through transfusion,organ transplantation including orthotopic liver transplantation,or hemodialysis.Donor screening before blood transfusion,prophylaxis for high-risk organ transplantation recipients,and dialysis-specific infection-control programs should be considered to reduce the risk of transmission.Second,OBI may reactivate and cause acute hepatitis in immunocompromised patients or those receiving chemotherapy.Close HBV DNA monitoring and timely antiviral treatment canprevent HBV reactivation and consequent clinical deterioration.Third,OBI may contribute to the progression of hepatic fibrosis in patients with chronic liver disease including hepatitis C.Finally,OBI seems to be a risk factor for hepatocellular carcinoma by its direct protooncogenic effect and by indirectly causing persistent hepatic inflammation and fibrosis.However,this needs further investigation.We review published reports in the literature to gain an overview of the status of OBI and emphasize the clinical importance of OBI.     

无偿献血人群隐匿性乙型肝炎病毒感染调查*

目的 调查无偿献血人群隐匿性乙型肝炎病毒感染(OBI)情况。方法 2021年1月～2021年12月我站无偿献血者血液样本107397份,采用两种ELISA法检测试剂盒进行HBsAg的初次筛查,采用核酸检测(NAT)法对两次HBsAg结果均为阴性的样本进行HBV DNA检测。对血清HBsAg阴性而HBV DNA阳性样本进行HBV血清学标志物检测,并采用实时荧光定量聚合酶链式反应(PCR)法检测核酸和病毒基因分型。 结果 在筛查的107397例无偿献血人群血样本中,经血清标志物检测后确认为OBI 者29例(0.27‰);血清抗-HBc阳性者12例(35.3%),抗-HBe/抗-HBc阳性者8例(23.5%),抗-HBs/抗-HBc阳性者6例(17.7%),抗-HBs/抗-HBe/抗-HBc阳性者3例(8.8%);19～29岁年龄段献血人群OBI感染率为0.09‰,30～39岁人群为0.32‰,40～49岁人群为0.39‰,50～55岁年龄段献血人群OBI感染率为0.41‰,且该年龄段重复献血者OBI感染率为0.31‰;血清抗-HBs/抗-HBc阳性和抗-HBs/抗-HBe/抗-HBc OBI献血者血清病毒载量>1000 IU/mL的占比分别为33.3%和66.7%,显著高于血清仅抗-HBc阳性者(0.0%,P<0.05)或血清抗-HBe/抗-HBc阳性者(0.0%,P<0.05);在29例OBI献血者中,C基因型占比为62.1%,B基因型感染占比为27.6%。结论 在初筛血清HBsAg 阴性的献血人群中,可能还存在很低比率的OBI人群,对用血安全提出了挑战。全面进行病毒核酸检测的花费-效益关系需要认真研究,提高常规ELISA检测方法的灵敏度也是关键。     

Hepatitis B virus blood screening: impact of nucleic amplification technology testing implementation on identifying hepatitis B surface antigen non-reactive window period and chronic infections

Background Despite improvements in hepatitis B surface antigen (HBsAg) test sensitivity, post‐transfusion hepatitis B virus (HBV) infection still occurs because HBsAg is undetectable during the early window phase (WP) of the infection, in the convalescence core window phase of the infection, or in serologically silent chronic hepatitis or in mutant forms of HBV. HBV‐DNA screening using high sensitivity nucleic amplification technology (NAT) assays has recently been introduced to reduce the residual risk of transmission of HBV by transfusion of blood components. Materials Over 1 year 75 063 donations were individually screened for HBV‐DNA by the Ultrio Procleix assay on the Tigris platform. The donations were collected in the Latium region, an area of the central Italy, and they accounted for the 40% of the total blood units collected in this area per year. The initial reactive samples were re‐tested and confirmed by the discriminatory HBV assay. Additional HBV serological markers were also performed. Suspected WP infections were followed‐up to monitor the development of the immune response. All HBV‐DNA‐positive donors were called back to check up their infectious status. Results The results of testing the 75 063 donations are: 33 donations HBsAg positive, 31 out of them HBV‐DNA‐positive and two HBV‐DNA negative; 22 donations HBsAg‐negative but HBV‐DNA positive with low viral load. Six of the 22 were found to be consistently HBV‐DNA reactive whereas the remaining 16 donations showed inconsistent results on multiple NAT retesting. One WP infection was confirmed by the follow‐up of the donor for 3 months following the index blood donation. Conclusions In the donor population of the Latium region, NAT screening has revealed a higher than expected number of donors who were HBsAg non‐reactive but HBV‐DNA‐positive with three donors showing HBV‐DNA as the only marker of infection. The adoption of genome screening has increased the safety of the blood supply and has also contributed to the protection of donor health by identifying either WP or clinically silent infections.     

Clinical significance of occult hepatitis B virus infection

Occult hepatitis B virus(HBV) infection(OBI) is defined as the presence of HBV DNA in the liver(with or without detectable HBV DNA in serum) for individuals testing HBV surface antigen negative.Until recently,the clinical effect of OBI was unclear on the progression of liver disease;on the development of hepatocellular carcinoma;and on the risk for reactivation or transmission of HBV infection.Several studies suggest a high prevalence of OBI among patients with cryptogenic chronic liver disease,but its role...     

Role of occult hepatitis B virus infection in chronic hepatitis C

The development of sensitive assays to detect small amounts of hepatitis B virus(HBV) DNA has favored the identification of occult hepatitis B infection(OBI), a virological condition characterized by a low level of HBV replication with detectable levels of HBV DNA in liver tissue but an absence of detectable surface antigen of HBV(HBs Ag) in serum. The gold standard to diagnose OBI is the detection of HBV DNA in the hepatocytes by highly sensitive and specific techniques, a diagnostic procedure requiring liver tissue to be tested and the use of non-standardized non-commercially available techniques. Consequently, in everyday clinical practice, the detection of anti-hepatitis B core antibody(antiHBc) in serum of HBs Ag-negative subjects is used as a surrogate marker to identify patients with OBI. In patients with chronic hepatitis C(CHC), OBI has been identified in nearly one-third of these cases. Considerable data suggest that OBI favors the increase of liver damage and the development of hepatocellular carcinoma(HCC) in patients with CHC. The data from other studies, however, indicate no influence of OBI on the natural history of CHC, particularly regarding the risk of developing HCC.     

Occult hepatitis B virus infection and its clinical implications

Occult hepatitis B virus (HBV) infection is characterized by presence of HBV infection with undetectable hepatitis B surface antigen (HBsAg). Serum HBV level is usually less than 10⁴ copies/mL in these patients. Diagnosis of occult HBV infection requires sensitive HBV-DNA PCR assay. Several possibilities have been hypothesized as the mechanisms of occult HBV infection. These include: (i) mutations of HBV-DNA sequence; (ii) integration of HBV-DNA into host's chromosomes; (iii) infection of peripheral blood mononuclear cells by HBV; (iv) formation of HBV-containing immune complex; (v) altered host immune response; and (vi) interference of HBV by other viruses. The precise prevalence of occult HBV infection remains to be defined. The clinical implications of occult HBV infection involve different clinical aspects. First of all, occult HBV infection harbours potential risk of HBV transmission through blood transfusion, haemodialysis, and organ transplantation. Second, it may serve as the cause of cryptogenic liver disease, contribute to acute exacerbation of chronic hepatitis B, or even fulminant hepatitis. Third, it is associated with development of hepatocellular carcinoma. Fourth, it may affect disease progression and treatment response of chronic hepatitis C. Most of the previous studies utilized retrospective observation without control groups, and lacked direct association of occult HBV infection with specific pathological changes and disease progression. Highly sensitive, quantitative, and functional molecular analyses of HBV, combined with a well-designed prospective clinical assessment will provide the best approach for the future study of occult HBV infection.     

Tissue donation and virus safety: more nucleic acid amplification testing is needed

A. Pruss, G. Caspari, D.H. Krüger, J. Blümel, C.M. Nübling, L. Gürtler, W.H. Gerlich. Tissue donation and virus safety: more nucleic acid amplification testing is needed.
Transpl Infect Dis 2010: 12: 375–386. All rights reserved Abstract: In tissue and organ transplantation, it is of great importance to avoid the transmission of blood‐borne viruses to the recipient. While serologic testing for anti‐human immunodeficiency virus (HIV)‐1 and ‐2, anti‐hepatitis C virus (HCV), hepatitis B surface antigen (HBsAg), anti‐hepatitis B core antigen (HBc), and Treponema pallidum infection is mandatory, there is until now in most countries no explicit demand for nucleic acid amplification testing (NAT) to detect HIV, hepatitis B virus (HBV), and HCV infection. After a review of reports in the literature on viral transmission events, tissue‐specific issues, and manufacturing and inactivation procedures, we evaluated the significance of HIV, HCV, and HBV detection using NAT in donors of various types of tissues and compared our results with the experiences of blood banking organizations. There is a significant risk of HIV, HCV, and HBV transmission by musculoskeletal tissues because of their high blood content and the high donor–recipient ratio. If no effective virus inactivation procedure for musculoskeletal tissue is applied, donors should be screened using NAT for HIV, HCV, and HBV. Serologically screened cardiovascular tissue carries a very low risk of HIV, HCV, or HBV transmission. Nevertheless, because effective virus inactivation is impossible (retention of tissue morphology) and the donor–recipient ratio may be as high as 1:10, we concluded that NAT should be performed for HIV, HCV, and HBV as an additional safety measure. Although cornea allografts carry the lowest risk of transmitting HIV, HCV, and HBV owing to corneal physiology, morphology, and the epidemiology of corneal diseases, NAT for HCV should still be performed. If the NAT screening of a donor for HIV, HCV, and HBV is negative, quarantine storage of the donor tissue seems dispensable. In view of numerous synergistic effects with transfusion medicine, it would be advantageous for tissue banks to cooperate with blood bank laboratories in performing virological tests.     

Clinical impact of occult hepatitis B virus infection in immunosuppressed patients

Occult hepatitis B infection(OBI), is characterized by low level hepatitis B virus(HBV) DNA in circulating blood and/or liver tissue. In clinical practice the presence of antibody to hepatitis B core antigen in hepatitis B surface antigen(HBsAg)-/anti-HBs-negative subjects is considered indicative of OBI. OBI is mostly observed in the window period of acute HBV infection in blood donors and in recipients of blood and blood products, in hepatitis C virus chronic carriers, in patients under pharmacological immunosuppression, and in those with immunodepression due to HIV infection or cancer. Reactivation of OBI mostly occurs in anti-HIV-positive subjects, in patients treated with immunosuppressive therapy in onco-hematological settings, in patients who undergo hematopoietic stem cell transplantation, in those treated with anti-CD20 or anti-CD52 monoclonal antibody, or anti-tumor necrosis factors antibody for rheumatological diseases, or chemotherapy for solid tumors. Under these conditions the mortality rate for hepatic failure or progression of the underlying disease due to discontinuation of specific treatment can reach 20%. For patients with OBI, prophylaxis with nucleot(s)ide analogues should be based on the HBV serological markers, the underlying diseases and the type of immunosuppressive treatment. Lamivudine prophylaxis is indicated in hemopoietic stem cell transplantation and in onco-hematological diseases when high dose corticosteroids and rituximab are used; monitoring may be indicated when rituximab-sparing schedules are used, but early treatment should be applied as soon as HBsAg becomes detectable. This review article presents an up-to-date evaluation of the current knowledge on OBI.