Effect of anti-viral therapy for occult hepatitis C virus infection M. PARDO*, J. M. LO ´ PEZ-ALCOROCHO*, I. CASTILLO*, E. RODRI ´ GUEZ-IN ˜ IGO*, A. PEREZ-MOTA   & V. CARREN ˜ O* *Fundacio ´n para el Estudio de las Hepatitis Virales, Madrid, Spain;  Digestive Department, Hospital Virgen de la Torre, Madrid, Spain Correspondence to: Dr V. Carren ˜ o, C/Guzma ´n el Bueno, 72, 28015 Madrid, Spain. E-mail: fehvhpa@fehv.org Publication data Submitted 26 December 2005 First decision 11 January 2006 Resubmitted 23 January 2006 Resubmitted 14 February 2006 Accepted 14 February 2006 SUMMARY Background Occult hepatitis C virus infection is defined by the presence of hepatitis C virus-RNA in liver but with undetectable anti-hepatitis C virus and serum viral RNA. Aim To study the response to anti-viral therapy in occult hepatitis C virus infection to assess the pathogenic effect of occult hepatitis C virus. Methods Ten patients with occult hepatitis C virus infection were treated with pegylated-interferon plus ribavirin for 24 weeks and were followed-up 24 weeks after therapy. All patients had abnormal alanine aminotrans- ferase, hepatitis C virus-RNA positive in peripheral blood mononuclear cells and liver necroinflammation. Results At the end of treatment and follow-up, the percentage of patients with normal alanine aminotransferase was 80% (95% CI: 48–96%) and 60% (95% CI: 31–84%) respectively, and hepatitis C virus-RNA in peripheral blood mononuclear cells was negative in 80% (95% CI: 48–96%) and 70% (95% CI: 40–90%) cases. At the end of follow-up sustained response was observed in 30% (95% CI: 11–61%) of cases. Five patients underwent a second liver biopsy. In all cases, liver hepatitis C virus- RNA persisted, although hepatitis C virus-RNA load was significantly lower (3.2 · 10 4  5.1 · 10 4 copies/lg RNA) than in the basal biopsy (2.4 · 10 5  3.8 · 10 5 copies/lg RNA); (P ¼ 0.043). Necroinflammation and fibrosis decreased in three cases. Conclusion The biochemical, virological and histological response to therapy achieved in patients with occult hepatitis C virus infection demonstrates the pathologic effects of occult hepatitis C virus. Aliment Pharmacol Ther 23, 1153–1159 Alimentary Pharmacology & Therapeutics ª 2006 The Authors 1153 Journal compilation ª 2006 Blackwell Publishing Ltd doi:10.1111/j.1365-2036.2006.02886.x