Phylogenetic analyses confirm the high prevalence of hepatitis C virus (HCV) type 4 in the Seine-Saint-Denis district (France) and indicate seven different HCV-4 subtypes linked to two different epidemiological patterns.

Hepatitis C virus (HCV) has been classified into six clades as a result of high genetic variability. In the Seine-Saint-Denis district of north-east Paris, the prevalence of HCV-4, which usually infects populations from Africa or the Middle East, is twice as high as that recorded for the whole of continental France (10·2 versus 4·5%). Although the pathogenicity of HCV-4 remains unknown, resistance of HCV-4 to therapy appears to be similar to that observed for HCV-1. In order to characterize the epidemiology of HCV-4 in Paris, sequences of the non-structural 5B gene (332 bp) were obtained from 38 HCV-4-infected patients. Extensive phylogenetic analyses indicated seven different HCV-4 subtypes. Moreover, phylogenetic tree topologies clearly distinguished two epidemiological profiles. The first profile (52·6% of patients) reflects the intra-suburban emergence of two distinct HCV-4 subclades occurring mainly among intravenous drug users (65% of patients). The second profile shows six subclades [HCV-4a, -4f, -4h, -4k, -4a(B) and a new sequence] and accounts for patients from Africa (Egypt and sub-Saharan countries) who have unknown risk factors (77·8% of patients) and in whom no recent diffusion of HCV-4 is evident. This study indicates the high diversity of HCV-4 and the extension of HCV-4a and -4d subclades among drug users in France.