Independent and additive effect modification of hepatitis C and B viruses infection on the development of chronic hepatitis

This study aimed to assess the effects and interaction between hepatitis B virus and hepatitis C virus infection on the development of chronic hepatitis. Methods: Anti-HCV and HBsAg were detected in 125 histology-proven chronic hepatitis and 250 sex-matched and age-matched healthy controls. Results: The prevalances of anti-HCV (24.8%) and HBsAg (68.0%) in patients were higher than in controls (2.4% and 18.0%, respectively; each p<0.0001). Univariate analysis showed that anti-HCV and HBsAg were strongly associated with the development of chronic hepatitis. Calculation of synergy index and Mantel extension test for trend indicated that there was additive effect modification between HCV and HBV. Multivariate analysis inidicated that anti-HCV (odds ratio, 46.1; 95% confidence interval, 9.1–233.2) and HBsAg (odds ratio, 25.8; 95% confidence interval (9.3–67.2) were independent risk factors of chronic hepatitis. The population-attributable risk was estimated as 15.6% for anti-HCV alone, 52.4% for HBsAg alone and 6.8% for both anti-HCV and HBsAg. The frequency of chronic active hepatitis in patients with anti-HCV alone (100%) was higher than in patients with HBsAg alone (75%, p<0.001). Conclusion: HCV and HBV infections are risk factors of chronic hepatitis. The act independently and probably with additive effect modification.