Interferon responsiveness in patients infected with hepatitis C virus 1b differs depending on viral subtype

Background - Genotype 1b of hepatitis C virus (HCV) comprises mainly three subtypes, each named for its geographic prevalence (worldwide, W; Japan, J; and not in Japan, NJ). Aim - To characterise the newly identified subtypes of genotype 1b and to review factors associated with response to interferon (IFN) for each subtype. Patients - Chronic hepatitis patients (80 men and 41 women; mean age 48.5 years, range 20.7-69.3) with HCV genotype 1b (W type, n=41; J type, n=38) or genotype 2a (n=42) were treated according to the same IFN protocol. Forty four patients (36.4%) negative for serum HCV RNA six months after cessation of treatment were considered complete responders. Methods - Factors associated with complete response were investigated. Results - Genotype 2a patients had lower viral loads (odds ratio 0.11 (95% confidence intervals (CI) 0.049-0.256)) and a better IFN response (odds ratio 0.25 (95% CI 0.117-0.552)) than genotype 1b patients whereas W type and J type patients had similar viral loads and responses to IFN. IFN response in W type patients was associated with female sex (odds ratio 0.23 (95% CI 0.055-0.983)) and low viral load (odds ratio 84.00 (95% CI 14.04-502.6)) whereas response in J type patients was related to transfusion history (odds ratio 7.20 (95% CI 1.443-35.91)), low viral load (odds ratio 117.0 (95% CI 17.82-768.3)), and genetic mutation in the interferon sensitivity determining region of the virus (odds ratio 0.08 (95% CI 0.013-0.553)). Multivariate analysis found low viral load (odds ratio 64.19 (95% CI 14.66-281.06)) to be the only significant independent factor associated with IFN response. Conclusions - Factors associated with IFN responsiveness in HCV infection differ with viral subtype.