Time-dependent events in natural history of occult hepatitis B virus infection: the importance of population-based long-term follow-up study with repeated measurements

Abstract

More than 350 million persons in the world are affected with chronic infection of hepatitis B virus (HBV) [[1]Lee W. Hepatitis B virus infection.N Engl J Med. 1997; 337: 1733-1745Crossref PubMed Scopus (2157) Google Scholar]. It is particularly prevalent in the Asian-Pacific region, where patients usually acquire the infection perinatally or in early childhood through iatrogenic transmission [[2]Chen C.J. Wang L.Y. Yu M.W. Epidemiology of hepatitis B virus infection in the Asia-Pacific region.J Gastroenterol Hepatol. 2000; 15: E3-E6Crossref PubMed Scopus (210) Google Scholar]. Chronic HBV infection is associated with an increased risk of liver cirrhosis, hepatic decompensation and hepatocellular carcinoma (HCC) [[3]Beasley R.P. Hepatitis B virus: the major etiology of hepatocellular carcinoma.Cancer. 1988; 61: 1942-1956Crossref PubMed Scopus (1157) Google Scholar], and 15–40% patients chronically infected with HBV will develop these serious sequelae during their lifetime [[4]McMahon B.J. Hepatocellular carcinoma and viral hepatitis.in: Wilson R.A. Viral hepatitis. Marcel Dekker, New York1997: 315-330Google Scholar]. Chronic HBV infection has been documented as the single most common cause of liver cirrhosis and HCC worldwide [[5]Lok A.S. McMahon B. Chronic hepatitis B.Hepatology. 2001; 34: 1225-1241Crossref PubMed Scopus (807) Google Scholar]. It is well known that HBV is not directly cytopathic, and the development of liver cirrhosis and HCC in patients with chronic HBV infection is a multistage process with involvement of multifactorial etiology including interactions between host and environmental factors [6Yu M.W. Hsu F.C. Sheen I.S. Chu C.M. Lin D.Y. Chen C.J. Liaw Y.F. Prospective study of hepatocellular carcinoma and liver cirrhosis in asymptomatic chronic hepatitis B virus carriers.Am J Epidemiol. 1997; 145: 1039-1047Crossref PubMed Scopus (257) Google Scholar, 7Chen C.J. Chen D.S. Interaction of hepatitis B virus, chemical carcinogen and genetic susceptibility: multistage hepatocarcinogenesis with multifactorial etiology.Hepatology. 2002; 36: 1046-1049Crossref PubMed Scopus (107) Google Scholar]. Other risk factors for chronic hepatitis B-related liver cirrhosis and HCC include gender, age, habits of cigarette smoking and alcohol consumption, exposures to chemical carcinogens, hormonal factors, as well as genetic susceptibility [6Yu M.W. Hsu F.C. Sheen I.S. Chu C.M. Lin D.Y. Chen C.J. Liaw Y.F. Prospective study of hepatocellular carcinoma and liver cirrhosis in asymptomatic chronic hepatitis B virus carriers.Am J Epidemiol. 1997; 145: 1039-1047Crossref PubMed Scopus (257) Google Scholar, 7Chen C.J. Chen D.S. Interaction of hepatitis B virus, chemical carcinogen and genetic susceptibility: multistage hepatocarcinogenesis with multifactorial etiology.Hepatology. 2002; 36: 1046-1049Crossref PubMed Scopus (107) Google Scholar, 8Chen C.J. Yu M.W. Liaw Y.F. Epidemiological characteristics and risk factors of hepatocellular carcinoma.J Gastroenterol Hepatol. 1997; 12: S294-S308Crossref PubMed Scopus (452) Google Scholar, 9Chen C.J. Yu M.W. Wang C.J. Huang H.Y. Lin W.C. Multiple risk factors of hepatocellular carcinoma: a cohort study of 13737 male adults in Taiwan.J Gastroenterol Hepatol. 1993; 8: S83-S87Crossref Scopus (33) Google Scholar].Chronic HBV infection is usually defined as the persistence of hepatitis B surface antigen (HBsAg) in serum for more than 6 months. HBsAg-seropositivity has been well documented as a major HCC risk factor in ecological correlation, case-control and cohort studies. The relative HCC risk for seropositivity of HBsAg ranges from 5 to 98-fold, with population attributable risk percentage ranging from 8 to 94% [[8]Chen C.J. Yu M.W. Liaw Y.F. Epidemiological characteristics and risk factors of hepatocellular carcinoma.J Gastroenterol Hepatol. 1997; 12: S294-S308Crossref PubMed Scopus (452) Google Scholar]. In addition to HBsAg, seropositivity of (HBeAg) hepatitis B e antigen, as a marker of active replication of HBV has been found to increase the risk of HCC in several case-control studies with a wide range in estimated relative risks [[10]You S.L. Yang H.I. Chen C.J. Seropositivity of hepatitis B e antigen and hepatocellular carcinoma.Ann Med. 2004; 36: 215-224Crossref PubMed Scopus (38) Google Scholar]. In a recent long-term follow-up study on 11,893 male residents in Taiwan, the relative HCC risk was 9.6 for seropositives of HBsAg only and 60.2 for seropositives of both HBsAg and HBeAg in comparison with those who were seronegative on both HBsAg and HBeAg [[11]Yang H.I. Lu S.N. You S.L. Sun C.A. Wang L.Y. Hsiao K. et al.Hepatitis B e antigens and the risk of hepatocellular carcinoma.N Engl J Med. 2002; 347: 168-174Crossref PubMed Scopus (1048) Google Scholar]. The increased HCC risk associated with seropositivity for HBeAg remained significant in stratification analyses by age, gender, habits of cigarette smoking and alcohol consumption, serum alanine aminotransferase level and liver cirrhosis status [10You S.L. Yang H.I. Chen C.J. Seropositivity of hepatitis B e antigen and hepatocellular carcinoma.Ann Med. 2004; 36: 215-224Crossref PubMed Scopus (38) Google Scholar, 12Chen C.J. Yang H.I. You S.L. Hepatitis B e antigen and hepatocellular carcinoma.N Engl J Med. 2002; 347: 1722Crossref PubMed Scopus (1) Google Scholar]. The variation in estimated relative and attributable risks for seropositivity of HBsAg and HBeAg in different studies may result from their differences in study design, selection of study subjects, comparability of comparison groups, control of confounding variables, period of follow-up, and prevalence of HBV infection in study populations.Despite the strong association between HCC and seropositivity of HBsAg, there remained HBsAg-seronegative patients affected with HCC and liver cirrhosis in almost all clinical and epidemiological studies. A significant proportion of them were seropositive on anti-HBs and anti-HBc and seronegative on antibodies against hepatitis C virus (anti-HCV), especially in areas where HBV infection was hyperendemic. Hepatocarcinogenesis has a long natural history with various time-dependent events occurring over a wide life span. Spontaneous seroconversion of HBV infection markers along with the increase in age as shown in Table 1 has been hypothesized to explain the increased risk of liver cirrhosis and HCC among HBsAg-seronegative subjects. In other words, HBsAg-seronegative patients affected with HCC at an old age were considered to be seropositive on HBsAg when they were young. Another explanation became plausible after a sensitive molecular method was developed to detect HBV DNA in liver, peripheral blood mononuclear cells (PBMCs) and serum recently [5Lok A.S. McMahon B. Chronic hepatitis B.Hepatology. 2001; 34: 1225-1241Crossref PubMed Scopus (807) Google Scholar, 13Gilbert N. Corden S. Ijaz S. Grant P.R. Tedder R.S. Boxall E.H. Comparison of commercial assays for the quantification of HBV DNA load in health care workers: caliberation differences.J Virol Methods. 2002; 100: 37-47Crossref PubMed Scopus (32) Google Scholar, 14Cabrerizo M. Bartolome J. Caramelo C. Barril G. Carreno V. Molecular analysis of hepatitis B virus DNA in serum and peripheral blood mononuclear cells from hepatitis B surface antigen-negative cases.Hepatology. 2000; 32: 116-123Crossref PubMed Scopus (140) Google Scholar]. A specific group of patients who are seronegative on HBsAg but seropositive on HBV DNA has been identified and defined as occult hepatitis B [15Torbenson M. Thomas D.L. Occult hepatitis B.Lancet Infect Dis. 2002; 2: 479-486Abstract Full Text Full Text PDF PubMed Scopus (445) Google Scholar, 16Hu K.Q. Occult hepatitis B virus infection and its clinical implications.J Viral Hepatitis. 2002; 9: 243-257Crossref PubMed Scopus (243) Google Scholar].Table 1Age-gender-specific seroprevalence of HBsAg, HBV DNA, and HBeAg among 23,820 men and women in TaiwanAge (year)HBsAgHBV DNAaSeroprevalence of HBsAg among residents multiplied by seroprevalence of HBV DNA/HBeAg among HBsAg-seropositives.HBeAgaSeroprevalence of HBsAg among residents multiplied by seroprevalence of HBV DNA/HBeAg among HBsAg-seropositives.MenWomenMenWomenMenWomen30–3924.215.219.511.25.83.240–4922.514.617.910.63.71.850–5919.214.414.110.82.01.560–6913.412.48.88.50.71.0a Seroprevalence of HBsAg among residents multiplied by seroprevalence of HBV DNA/HBeAg among HBsAg-seropositives. Open table in a new tab Although occult hepatitis B has been well documented since 1978 [[17]Hoofnagle J.H. Seef L.B. Bales Z.B. Zimmerman H.J. The type B hepatitis after transfusion with blood containg antibody to hepatitis B core antigen.N Engl J Med. 1978; 298: 1379-1383Crossref PubMed Scopus (370) Google Scholar], it had not been well studied until HBV polymerase chain reaction became available. The molecular and immunological mechanisms underlying occult hepatitis B remain incompletely elucidated. Several hypotheses have been proposed for the occurrence of occult HBV infection. They included the mutation of HBV surface, core and X genes, the integration of HBV DNA into host genomes, the HBV infection of PBMCs, the formation of circulating immune complex containing HBV, the altered host immune response to HBV, and the superinfection and interference of HBV by other viruses. The occult HBV infection may transmit HBV through transfusion, hemodialysis, and organ transplantation. It may contribute to acute exacerbation of chronic hepatitis B and even fulminant hepatitis, and development of HCC. It also affects disease progression and treatment response of chronic hepatitis C [15Torbenson M. Thomas D.L. Occult hepatitis B.Lancet Infect Dis. 2002; 2: 479-486Abstract Full Text Full Text PDF PubMed Scopus (445) Google Scholar, 16Hu K.Q. Occult hepatitis B virus infection and its clinical implications.J Viral Hepatitis. 2002; 9: 243-257Crossref PubMed Scopus (243) Google Scholar].There is a wide variation in prevalence of occult hepatitis B among various patient groups, blood and organ donors, and healthy controls. The prevalence of seropositivity of HBV DNA in HBsAg-seronegative subjects ranges 0–10% among those without liver diseases, 11–19% in patients affected with chronic hepatitis, 12–61% in HCC patients, and 1–95% in patients with HCV infection [[18]Brechot C. Thiers V. Kremsdorf D. Nalpas B. Pol S. Paterlini-Brechot P. Persistent hepatitis B virus infection in subjects without hepatitis B surface antigen: clinically significant or purely occult?.Hepatology. 2001; 34: 194-203Crossref PubMed Scopus (491) Google Scholar]. However, most previous studies on occult hepatitis B are small retrospective clinical studies without comparable controls or clinical trials with a small sample size. The comparison of findings from these studies was limited by the differences in laboratory methods for detection and quantification of free and/or bound HBV DNA, stratification analyses by serostatus of anti-HBs and anti-HBc, diagnostic criteria and clinical stage of various liver diseases, source and selection of patients and unaffected controls, comparability between comparison groups, sample size and statistical power, control of confounding factors, single random or multiple repeated measurements of HBV infection markers, duration and loss of follow-up, and randomization and compliance with a controlled trial.Two papers on occult hepatitis B appear in this issue of the Journal [19Minuk G.Y. Sun D. Uhanova J. Zhang M. Caouette S. Nicolle L.E. et al.Occult hepatitis B virus infection in a North American community-based population.J Hepatol. 2005; 42: 480-485Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 20Gregorek H. Dzierżanowska-Fangrat K. Woynarowski M. Jóźwiak P. Witkowska-Vogtt E. Socha J. et al.Persistence of HBV-DNA in children with chronic hepatitis B who seroconverted to anti-HBs antibodies after interferon-α therapy: correlation with specific IgG subclass responses to HBsAg.J Hepatol. 2005; 42: 486-490Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. One is a cross-sectional survey on the prevalence of occult hepatitis B among 487 HBsAg-seronegative residents in a Canadian Inuit community [[19]Minuk G.Y. Sun D. Uhanova J. Zhang M. Caouette S. Nicolle L.E. et al.Occult hepatitis B virus infection in a North American community-based population.J Hepatol. 2005; 42: 480-485Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar]. The prevalence of HBV DNA detectable in serum was 8% among those who were seronegative on HBsAg, anti-HBs and anti-HBc, and 18% among HBsAg-seronegatives who were seropositive on anti-HBc and anti-HBs. Furthermore, the prevalence of S-variants was 52 and 86% in these two groups, respectively. This study did not find any association with occult hepatitis B for age, gender, and serum levels of alanine aminotransferase and total bilirubin. This is one of few reports on seroprevalence of occult hepatitis B at a population-based level. It had a representative sample of study population and standardized laboratory methods. However, its small number of patients affected with occult hepatitis limits the statistical power to examine the trend of age-specific prevalence occult hepatitis B. Its cross-sectional design using one random serum sample from each resident also limits the clarification of disease progression and causal temporality between occult hepatitis B and S-variant. The findings of this study provide important implications for the healthcare of hepatitis B. As the prevalence of occult hepatitis, which may progress to liver cirrhosis and HCC, may be as high as 8–18% among HBsAg-seronegatives; it is essential to test their HBV DNA for the prevention and early detection of liver diseases in the hyperendemic area of HBV.The other paper in the Journal is a clinical follow-up study on occult hepatitis B among 38 children treated with interferon-α and 19 controls with spontaneous loss of HBsAg [[20]Gregorek H. Dzierżanowska-Fangrat K. Woynarowski M. Jóźwiak P. Witkowska-Vogtt E. Socha J. et al.Persistence of HBV-DNA in children with chronic hepatitis B who seroconverted to anti-HBs antibodies after interferon-α therapy: correlation with specific IgG subclass responses to HBsAg.J Hepatol. 2005; 42: 486-490Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. HBV DNA was detectable in 13 (35%) of 37 children who became HBsAg-seronegative and anti-HBs-seropositive after interferon-α treatment, and in 3 (16%) of controls with spontaneous seroconversion. Children treated with interferon-α had significantly (P<0.05) higher percentages of IgG3 and IgG4 in total anti-HBs response (20 and 24%, respectively) than controls with spontaneous loss of HBsAg (9 and 7%, respectively). Among interferon-α-treated children, the percentages of IgG3 and IgG 4 in total anti-HBs response were significantly different between 13 seropositives and 24 seronegatives of HBV DNA (9 vs. 18%, P<0.05 for IgG3; 29 vs. 6%, P<0.001 for IgG4). These two comparison groups were not comparable with regards to age and gender, and the frequency distribution of unstudied confounding factors may also be different. However, this study suggests HBV DNA may persist for a long time after interferon-α treatment and a possibility of using specific IgG subclasses to predict persistence of HBV DNA. As the children involved in the study were young and the follow-up period was short, it could not examine progressive clinical outcomes associated with HBV DNA persistence after treatment.As occult hepatitis B is an important clinical entity which may progress to severe sequelae, in-depth study of its natural history is essential. The molecular mechanism, dynamic fluctuation, and health risk of occult hepatitis cannot be accurately delineated through cross-sectional survey, case series studies or case-control studies. The best approach is a population-based long-term follow-up study on a randomly selected cohort with repeated measurements of HBV infection markers including anti-HBs, anti-HBc, anti-HBe, HBsAg, HBeAg, and HBV DNA. As both environmental and genetic determinants are involved in the development of occult hepatitis B and consequent liver cirrhosis and HCC, these risk factors should also be included in the study. Periodical health examinations of study subjects may provide useful information on their clinical outcomes. Only such a comprehensive study carried out by a multidisciplinary research team can delineate time-dependent events in development and progression of occult hepatitis B and its related liver diseases. More than 350 million persons in the world are affected with chronic infection of hepatitis B virus (HBV) [[1]Lee W. Hepatitis B virus infection.N Engl J Med. 1997; 337: 1733-1745Crossref PubMed Scopus (2157) Google Scholar]. It is particularly prevalent in the Asian-Pacific region, where patients usually acquire the infection perinatally or in early childhood through iatrogenic transmission [[2]Chen C.J. Wang L.Y. Yu M.W. Epidemiology of hepatitis B virus infection in the Asia-Pacific region.J Gastroenterol Hepatol. 2000; 15: E3-E6Crossref PubMed Scopus (210) Google Scholar]. Chronic HBV infection is associated with an increased risk of liver cirrhosis, hepatic decompensation and hepatocellular carcinoma (HCC) [[3]Beasley R.P. Hepatitis B virus: the major etiology of hepatocellular carcinoma.Cancer. 1988; 61: 1942-1956Crossref PubMed Scopus (1157) Google Scholar], and 15–40% patients chronically infected with HBV will develop these serious sequelae during their lifetime [[4]McMahon B.J. Hepatocellular carcinoma and viral hepatitis.in: Wilson R.A. Viral hepatitis. Marcel Dekker, New York1997: 315-330Google Scholar]. Chronic HBV infection has been documented as the single most common cause of liver cirrhosis and HCC worldwide [[5]Lok A.S. McMahon B. Chronic hepatitis B.Hepatology. 2001; 34: 1225-1241Crossref PubMed Scopus (807) Google Scholar]. It is well known that HBV is not directly cytopathic, and the development of liver cirrhosis and HCC in patients with chronic HBV infection is a multistage process with involvement of multifactorial etiology including interactions between host and environmental factors [6Yu M.W. Hsu F.C. Sheen I.S. Chu C.M. Lin D.Y. Chen C.J. Liaw Y.F. Prospective study of hepatocellular carcinoma and liver cirrhosis in asymptomatic chronic hepatitis B virus carriers.Am J Epidemiol. 1997; 145: 1039-1047Crossref PubMed Scopus (257) Google Scholar, 7Chen C.J. Chen D.S. Interaction of hepatitis B virus, chemical carcinogen and genetic susceptibility: multistage hepatocarcinogenesis with multifactorial etiology.Hepatology. 2002; 36: 1046-1049Crossref PubMed Scopus (107) Google Scholar]. Other risk factors for chronic hepatitis B-related liver cirrhosis and HCC include gender, age, habits of cigarette smoking and alcohol consumption, exposures to chemical carcinogens, hormonal factors, as well as genetic susceptibility [6Yu M.W. Hsu F.C. Sheen I.S. Chu C.M. Lin D.Y. Chen C.J. Liaw Y.F. Prospective study of hepatocellular carcinoma and liver cirrhosis in asymptomatic chronic hepatitis B virus carriers.Am J Epidemiol. 1997; 145: 1039-1047Crossref PubMed Scopus (257) Google Scholar, 7Chen C.J. Chen D.S. Interaction of hepatitis B virus, chemical carcinogen and genetic susceptibility: multistage hepatocarcinogenesis with multifactorial etiology.Hepatology. 2002; 36: 1046-1049Crossref PubMed Scopus (107) Google Scholar, 8Chen C.J. Yu M.W. Liaw Y.F. Epidemiological characteristics and risk factors of hepatocellular carcinoma.J Gastroenterol Hepatol. 1997; 12: S294-S308Crossref PubMed Scopus (452) Google Scholar, 9Chen C.J. Yu M.W. Wang C.J. Huang H.Y. Lin W.C. Multiple risk factors of hepatocellular carcinoma: a cohort study of 13737 male adults in Taiwan.J Gastroenterol Hepatol. 1993; 8: S83-S87Crossref Scopus (33) Google Scholar]. Chronic HBV infection is usually defined as the persistence of hepatitis B surface antigen (HBsAg) in serum for more than 6 months. HBsAg-seropositivity has been well documented as a major HCC risk factor in ecological correlation, case-control and cohort studies. The relative HCC risk for seropositivity of HBsAg ranges from 5 to 98-fold, with population attributable risk percentage ranging from 8 to 94% [[8]Chen C.J. Yu M.W. Liaw Y.F. Epidemiological characteristics and risk factors of hepatocellular carcinoma.J Gastroenterol Hepatol. 1997; 12: S294-S308Crossref PubMed Scopus (452) Google Scholar]. In addition to HBsAg, seropositivity of (HBeAg) hepatitis B e antigen, as a marker of active replication of HBV has been found to increase the risk of HCC in several case-control studies with a wide range in estimated relative risks [[10]You S.L. Yang H.I. Chen C.J. Seropositivity of hepatitis B e antigen and hepatocellular carcinoma.Ann Med. 2004; 36: 215-224Crossref PubMed Scopus (38) Google Scholar]. In a recent long-term follow-up study on 11,893 male residents in Taiwan, the relative HCC risk was 9.6 for seropositives of HBsAg only and 60.2 for seropositives of both HBsAg and HBeAg in comparison with those who were seronegative on both HBsAg and HBeAg [[11]Yang H.I. Lu S.N. You S.L. Sun C.A. Wang L.Y. Hsiao K. et al.Hepatitis B e antigens and the risk of hepatocellular carcinoma.N Engl J Med. 2002; 347: 168-174Crossref PubMed Scopus (1048) Google Scholar]. The increased HCC risk associated with seropositivity for HBeAg remained significant in stratification analyses by age, gender, habits of cigarette smoking and alcohol consumption, serum alanine aminotransferase level and liver cirrhosis status [10You S.L. Yang H.I. Chen C.J. Seropositivity of hepatitis B e antigen and hepatocellular carcinoma.Ann Med. 2004; 36: 215-224Crossref PubMed Scopus (38) Google Scholar, 12Chen C.J. Yang H.I. You S.L. Hepatitis B e antigen and hepatocellular carcinoma.N Engl J Med. 2002; 347: 1722Crossref PubMed Scopus (1) Google Scholar]. The variation in estimated relative and attributable risks for seropositivity of HBsAg and HBeAg in different studies may result from their differences in study design, selection of study subjects, comparability of comparison groups, control of confounding variables, period of follow-up, and prevalence of HBV infection in study populations. Despite the strong association between HCC and seropositivity of HBsAg, there remained HBsAg-seronegative patients affected with HCC and liver cirrhosis in almost all clinical and epidemiological studies. A significant proportion of them were seropositive on anti-HBs and anti-HBc and seronegative on antibodies against hepatitis C virus (anti-HCV), especially in areas where HBV infection was hyperendemic. Hepatocarcinogenesis has a long natural history with various time-dependent events occurring over a wide life span. Spontaneous seroconversion of HBV infection markers along with the increase in age as shown in Table 1 has been hypothesized to explain the increased risk of liver cirrhosis and HCC among HBsAg-seronegative subjects. In other words, HBsAg-seronegative patients affected with HCC at an old age were considered to be seropositive on HBsAg when they were young. Another explanation became plausible after a sensitive molecular method was developed to detect HBV DNA in liver, peripheral blood mononuclear cells (PBMCs) and serum recently [5Lok A.S. McMahon B. Chronic hepatitis B.Hepatology. 2001; 34: 1225-1241Crossref PubMed Scopus (807) Google Scholar, 13Gilbert N. Corden S. Ijaz S. Grant P.R. Tedder R.S. Boxall E.H. Comparison of commercial assays for the quantification of HBV DNA load in health care workers: caliberation differences.J Virol Methods. 2002; 100: 37-47Crossref PubMed Scopus (32) Google Scholar, 14Cabrerizo M. Bartolome J. Caramelo C. Barril G. Carreno V. Molecular analysis of hepatitis B virus DNA in serum and peripheral blood mononuclear cells from hepatitis B surface antigen-negative cases.Hepatology. 2000; 32: 116-123Crossref PubMed Scopus (140) Google Scholar]. A specific group of patients who are seronegative on HBsAg but seropositive on HBV DNA has been identified and defined as occult hepatitis B [15Torbenson M. Thomas D.L. Occult hepatitis B.Lancet Infect Dis. 2002; 2: 479-486Abstract Full Text Full Text PDF PubMed Scopus (445) Google Scholar, 16Hu K.Q. Occult hepatitis B virus infection and its clinical implications.J Viral Hepatitis. 2002; 9: 243-257Crossref PubMed Scopus (243) Google Scholar]. Although occult hepatitis B has been well documented since 1978 [[17]Hoofnagle J.H. Seef L.B. Bales Z.B. Zimmerman H.J. The type B hepatitis after transfusion with blood containg antibody to hepatitis B core antigen.N Engl J Med. 1978; 298: 1379-1383Crossref PubMed Scopus (370) Google Scholar], it had not been well studied until HBV polymerase chain reaction became available. The molecular and immunological mechanisms underlying occult hepatitis B remain incompletely elucidated. Several hypotheses have been proposed for the occurrence of occult HBV infection. They included the mutation of HBV surface, core and X genes, the integration of HBV DNA into host genomes, the HBV infection of PBMCs, the formation of circulating immune complex containing HBV, the altered host immune response to HBV, and the superinfection and interference of HBV by other viruses. The occult HBV infection may transmit HBV through transfusion, hemodialysis, and organ transplantation. It may contribute to acute exacerbation of chronic hepatitis B and even fulminant hepatitis, and development of HCC. It also affects disease progression and treatment response of chronic hepatitis C [15Torbenson M. Thomas D.L. Occult hepatitis B.Lancet Infect Dis. 2002; 2: 479-486Abstract Full Text Full Text PDF PubMed Scopus (445) Google Scholar, 16Hu K.Q. Occult hepatitis B virus infection and its clinical implications.J Viral Hepatitis. 2002; 9: 243-257Crossref PubMed Scopus (243) Google Scholar]. There is a wide variation in prevalence of occult hepatitis B among various patient groups, blood and organ donors, and healthy controls. The prevalence of seropositivity of HBV DNA in HBsAg-seronegative subjects ranges 0–10% among those without liver diseases, 11–19% in patients affected with chronic hepatitis, 12–61% in HCC patients, and 1–95% in patients with HCV infection [[18]Brechot C. Thiers V. Kremsdorf D. Nalpas B. Pol S. Paterlini-Brechot P. Persistent hepatitis B virus infection in subjects without hepatitis B surface antigen: clinically significant or purely occult?.Hepatology. 2001; 34: 194-203Crossref PubMed Scopus (491) Google Scholar]. However, most previous studies on occult hepatitis B are small retrospective clinical studies without comparable controls or clinical trials with a small sample size. The comparison of findings from these studies was limited by the differences in laboratory methods for detection and quantification of free and/or bound HBV DNA, stratification analyses by serostatus of anti-HBs and anti-HBc, diagnostic criteria and clinical stage of various liver diseases, source and selection of patients and unaffected controls, comparability between comparison groups, sample size and statistical power, control of confounding factors, single random or multiple repeated measurements of HBV infection markers, duration and loss of follow-up, and randomization and compliance with a controlled trial. Two papers on occult hepatitis B appear in this issue of the Journal [19Minuk G.Y. Sun D. Uhanova J. Zhang M. Caouette S. Nicolle L.E. et al.Occult hepatitis B virus infection in a North American community-based population.J Hepatol. 2005; 42: 480-485Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, 20Gregorek H. Dzierżanowska-Fangrat K. Woynarowski M. Jóźwiak P. Witkowska-Vogtt E. Socha J. et al.Persistence of HBV-DNA in children with chronic hepatitis B who seroconverted to anti-HBs antibodies after interferon-α therapy: correlation with specific IgG subclass responses to HBsAg.J Hepatol. 2005; 42: 486-490Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. One is a cross-sectional survey on the prevalence of occult hepatitis B among 487 HBsAg-seronegative residents in a Canadian Inuit community [[19]Minuk G.Y. Sun D. Uhanova J. Zhang M. Caouette S. Nicolle L.E. et al.Occult hepatitis B virus infection in a North American community-based population.J Hepatol. 2005; 42: 480-485Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar]. The prevalence of HBV DNA detectable in serum was 8% among those who were seronegative on HBsAg, anti-HBs and anti-HBc, and 18% among HBsAg-seronegatives who were seropositive on anti-HBc and anti-HBs. Furthermore, the prevalence of S-variants was 52 and 86% in these two groups, respectively. This study did not find any association with occult hepatitis B for age, gender, and serum levels of alanine aminotransferase and total bilirubin. This is one of few reports on seroprevalence of occult hepatitis B at a population-based level. It had a representative sample of study population and standardized laboratory methods. However, its small number of patients affected with occult hepatitis limits the statistical power to examine the trend of age-specific prevalence occult hepatitis B. Its cross-sectional design using one random serum sample from each resident also limits the clarification of disease progression and causal temporality between occult hepatitis B and S-variant. The findings of this study provide important implications for the healthcare of hepatitis B. As the prevalence of occult hepatitis, which may progress to liver cirrhosis and HCC, may be as high as 8–18% among HBsAg-seronegatives; it is essential to test their HBV DNA for the prevention and early detection of liver diseases in the hyperendemic area of HBV. The other paper in the Journal is a clinical follow-up study on occult hepatitis B among 38 children treated with interferon-α and 19 controls with spontaneous loss of HBsAg [[20]Gregorek H. Dzierżanowska-Fangrat K. Woynarowski M. Jóźwiak P. Witkowska-Vogtt E. Socha J. et al.Persistence of HBV-DNA in children with chronic hepatitis B who seroconverted to anti-HBs antibodies after interferon-α therapy: correlation with specific IgG subclass responses to HBsAg.J Hepatol. 2005; 42: 486-490Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. HBV DNA was detectable in 13 (35%) of 37 children who became HBsAg-seronegative and anti-HBs-seropositive after interferon-α treatment, and in 3 (16%) of controls with spontaneous seroconversion. Children treated with interferon-α had significantly (P<0.05) higher percentages of IgG3 and IgG4 in total anti-HBs response (20 and 24%, respectively) than controls with spontaneous loss of HBsAg (9 and 7%, respectively). Among interferon-α-treated children, the percentages of IgG3 and IgG 4 in total anti-HBs response were significantly different between 13 seropositives and 24 seronegatives of HBV DNA (9 vs. 18%, P<0.05 for IgG3; 29 vs. 6%, P<0.001 for IgG4). These two comparison groups were not comparable with regards to age and gender, and the frequency distribution of unstudied confounding factors may also be different. However, this study suggests HBV DNA may persist for a long time after interferon-α treatment and a possibility of using specific IgG subclasses to predict persistence of HBV DNA. As the children involved in the study were young and the follow-up period was short, it could not examine progressive clinical outcomes associated with HBV DNA persistence after treatment. As occult hepatitis B is an important clinical entity which may progress to severe sequelae, in-depth study of its natural history is essential. The molecular mechanism, dynamic fluctuation, and health risk of occult hepatitis cannot be accurately delineated through cross-sectional survey, case series studies or case-control studies. The best approach is a population-based long-term follow-up study on a randomly selected cohort with repeated measurements of HBV infection markers including anti-HBs, anti-HBc, anti-HBe, HBsAg, HBeAg, and HBV DNA. As both environmental and genetic determinants are involved in the development of occult hepatitis B and consequent liver cirrhosis and HCC, these risk factors should also be included in the study. Periodical health examinations of study subjects may provide useful information on their clinical outcomes. Only such a comprehensive study carried out by a multidisciplinary research team can delineate time-dependent events in development and progression of occult hepatitis B and its related liver diseases.