Identification of hepatitis C viruses with a nonconserved sequence of the 5' untranslated region

The nucleotide sequence of the 5' untranslated region of hepatitis C virus (HCV) has been shown to be conserved. In contrast, we have detected more sequence variation in this region in several HCV isolates than hitherto expected. The nucleotide sequences of the 5' untranslated regions of these isolates differ significantly from that of the prototype but are very similar to each other. We believe that these isolates belong to the same type of HCV. Among 240 HCV RNA polymerase chain reaction-positive specimens that we examined, 7 belong to this type. The results suggest that the HCV variants that we detected represent a different type of HCV and that they are responsible for approximately 3% of HCV infections in patients that we have examined.