Characteristics of hepatitis C virus before and after interferon treatment in patients with ongoing viraemia but sustained biochemical response

In hepatitis C virus (HCV) infection, persistent viraemia can occur after successful biochemical response to interferon treatment. To assess whether this unusual profile might be due to trivial amounts of remaining virus or to the emergence of less pathogenic HCV strains, pre-and posttreatment sera from 27 patients who remained with HCV-RNA, despite sustained transaminase normalisation after interferon therapy, were investigated. All but one had infection by genotype 2 (P <0.0001), and levels of HCV-RNA were not decreased after therapy. Sequence comparison of the 5' untranslated region revealed mixed viral populations and 'not compensatory' nucleotide transitions localised at the stem level of the secondary structure of this region in samples taken before and after treatment. Neither quantitative nor qualitative viral changes, at least for the 5' untranslated region, are responsible for interferon-induced biochemical remission in these patients typically infected by genotype 2.