Alavian S M et al. donors (4), hemodialysis patients (5), healthy carriers, patients with cryptogenic advanced liver fibrosis (6), and special high-risk patients. 2. Evidence Acquisition The primary aims of this review were to: first, classify the different aspects of occult hepatitis in terms of clini- cal classification. Second, to describe the prevalence of OBH in different clinical settings. Third, to introduce an up to date information regarding the clinical and transmission aspects of OBH. A comprehensive search of PubMed was performed with the following Mesh term search using keyword: occult hepatitis B infection along with keywords: HCV, HIV, Immunosuppression, HCC, transfusion and transplantation. All published data since 2001 (the explanation of OBH) until May 2012 have been included in the study. The inclusion criteria for the study were: all studies that shown the presence of HBV DNA in the absence of HBsAg regardless of antibodies to core and/or surface proteins. 3. Results 3.1. Transfusion Settings The blood-safety issues related to the blood compo- nents or tissues of HBsAg-negative donors and the risk of transmission are of great concern. Medical research- ers fear that OHBI may be spread by blood transfusion because HBV-DNAHBV DNA detection by nucleic acid am- Occult Hepatitis B (OBH) in Clinical Settings plification technology is not mandatory for blood-donor screening in many countries, especially in those areas where the prevalence of escape mutants is expected to be high. Occult HBV infection may occur in several situ- ations and, as a result, may be transmitted to other in- dividuals through transfusion. Such situations include recovery from infection that leads to the production of anti-HBs but is characterized by persistent low-grade vi- remia, production of ‘escape’ mutants that cannot be de- tected by HBsAg testing, “carriers” with antibody to the hepatitis B e antigen (anti-HBe) and anti-HBc, and carriers that are negative for anti-HBe and anti-HBc. Although all of these situations can raise the transmission of HBV in the immune compromised, only the anti-HBc-positive, HBV-DNA-positive situation is infectious in the immune competent setting. Furthermore, Studies have clearly indicated that transfusion of HBsAg-negative, HBV DNA positive blood donor in blood supply was associated with the development of post-transfusion hepatitis B (7-9). The prevalence of OHB among HBsAg-negative donors varies in different parts of the world, and as mentioned above, depends on the endemicity of HBsAg carriers as well as the method used to test the virus. Reports from subsets of donors from North America and Western Europe have ranged from as low as 0 % (presence of anti-HBc) (10, 11) to as high as 2.8 % (isolated anti-HBc) (12, 13). Similarly, stud- ies from Asia (especially from highly endemic regions) have indicated prevalence rates of HBV-DNAHBV DNA de- tection among blood donors ranging from 0.13 (presence Table 1. Reported Prevalence of OHBI Obtained From Blood Specimens Collected From Different Clinical Settings OHB a Prevalence, % Prevalence of OHB in Anti-HBc a Positive Patients, % Clinical Setting Blood donors b HIV a HCV a HCC a,c Dialysis Immunosuppression Chronic HBV carriers Cryptogenic cirrhosis Transplantation Liver Stem Cell Kidney HBV a vaccinated Family contact of HBsAg positive carriers General Healthy Population d Hemophilia 0.05-13 0-89 6.7-91 12-80 3.3-37.8 0-58 5-55 4.8-40 36-64 0-50 0-3.3 2.7-28 8.8- 28.8 0.7-34 5.3-51.2 0-17 9-44 28-71 28.8-64 37.8-62.3 6.4-64.7 7-60 17.8-100 3-100 4.4-100 3-10 6.5-100 23.6-96.4 6.1-51 6-100 a Abbreviations: HBc, hepatitis B core; HBV, hepatitis B virus; HCC, hepatocellular carcinoma; HCV, hepatitis C virus; HIV, human immunodeficiency virus; OHB, Occult hepatitis B. b The lower and upper limits are in the presence of other serologic evidence and isolated- anti-HBc, respectively. c No HCV-related HCC. d Highly dependent on the geographic prevalence of HBV. 2 Published by Kowsar, © BRCGL 2012 Hepat Mon. 2012;12(8):e6126