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Abstract
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.