Clinical impact of occult HBV infections

HBV infection in the absence of HBsAg has been a matter of debate for years, but its existence and clinical relevance are now supported by many publications, editorials and reviews. HBV DNA without HBs antigenemia was detected in the following clinical situations: (1) Chronic, presumably viral, hepatitis unrelated to HCV, atypical alcoholic hepatitis and hepatocellular carcinoma (HCC); (2) viral reactivation following immunosuppression; (3) Transmission through transplantation, transfusion or experimental transmission to chimpanzees. Occult HBV infections are not restricted to areas of high HBV endemicity. Indeed, such cases have been described in Western countries including France. It is now established that occult HBV infection among non-HCV patients suffering from chronic hepatitis varies from 20% to 30% in Europe, and in the context of HCV infection it varies from 20% in France up to 80% in Japan. The percentage of occult HBV infections among non A-E cases depends on several parameters: (1) The method of detection, including PCR primer selection; (2) patient recruitment; (3) patients from countries highly endemic for HBV are more likely to develop occult HBV infections; (4) prevalence may also vary depending on the nature of biological material tested, with a higher proportion for liver compared to serum specimen. The mechanisms leading to HCC in occult HBV infection seem similar to those overt cases, patients with low-grade but diagnosable HBV replication that retains its pro-oncogenic properties. During the course of HCV infection, occult HBV infection may worsen liver damage induced by HCV and reduce the response to HCV antiviral treatment. Occult HBV infection is a frequent phenomenon and HBV DNA testing with highly sensitive PCR in the clinical setting is therefore becoming of paramount importance.