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.

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.