Mixed infection with two types of hepatitis C virus is probably a rare event.

A search for the simultaneous presence of two hepatitis C virus (HCV) types in sera of a group of chronically infected intravenous drug users, hemodialysis patients and hemophiliacs from Sweden and Russia was performed with two genotyping methods based on the use of type-specific primers from core and NS4 regions of the viral genome. An important feature of NS4 based assay is that type-specific primers are used in both rounds of nested PCR, thus providing the possibility of the identification not only of the abundant type, but also of the minor HCV type present in a particular serum. The experiments, however, did not reveal the simultaneous presence of two or more HCV types in any of the 40 samples. These results suggest that the frequency of mixed infections in serum with different HCV types is very low even in high-risk groups, at least in the geographic region studied.