TT virus (TTV) has been identified in patients with posttransfusion hepatitis of unknown etiology and is thought to be a new hepatitis virus. We determined the extent of TTV infection in the Japanese general population and the relationship between TTV DNA genotype and liver damage. In 1998, we tested 847 serum samples for TTV. TTV DNA was assayed by a nested polymerase chain reaction and classified into three different genotypes and eight subtypes. TTV DNA was detected in 25.3% and 32.4% of the inhabitants of the two areas studied, respectively. The genotype distribution was similar in both areas. G1, G2, and G3 were 60%, 20%, and 5%, respectively. Of the 20 subjects with TTV DNA alone and elevated serum ALT levels, 18 were G1, one was G2, and one was G3. TTV infection is endemic in the Japanese general population studied. The main TTV genotype, G1, may be related to the ensuing liver damage.
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