A new method for hepatitis C virus (HCV) genotyping that analyzes products generated with the HCV Amplicor Monitor Test has been developed. One hundred and sixty-two Japanese patients with chronic hepatitis C, including 59 patients with hemophilia, were tested for HCV genotypes and viral loads with this new test, and the results were compared with those of a genotyping assay that involved direct sequencing of the E1 region. HCV genotypes and viral loads were also compared between patients with and without hemophilia. There were no discrepancies between the two methods in determining genotypes 2a, 2b, and 3a. However, two patients infected with 1a were mistyped as 1b with the new assay. One patient not classified by this assay was genotype 4. Genotypes found in patients without hemophilia were 1b, 2a, and 2b. Genotypes 1a, 3a, and 4, which were minor variants in Japan, were detected only in patients with hemophilia. In addition, J type, which is a subtype of 1b that originated in Japan, was found at low frequency in hemophiliacs. Thus, the HCV genotypes in patients with hemophilia are likely to be of foreign origin. Overall, this new assay was accurate except for genotype 1a and 4, and allowed simultaneous assessment of genotype and viral load.
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