Hepatitis C virus genotype

Tests may also be performed to determine HCV genotype. HCV has six major genotypes, which occur with different frequency in different parts of the world. Genotypes 1a and 1b are most common in Europe and the United States, and are the most difficult to treat. Genotype 3 is frequently seen in IDUs. Genotype tests can help guide hepatitis C treatment. People with genotype 1 typically require more aggressive treatment, usually lasting at least 48 weeks. People with genotypes 2 or 3 are typically treated for 24 weeks. Genotype 4, which accounts for a majority of cases in the Middle East and parts of Africa, has traditionally been considered difficult to treat, like genotype 1. However, some recent research suggests that it might respond to interferon therapy better than previously thought.¹

Some research suggests that different genotypes are associated with different degrees of liver disease severity and rate of progression. Genotype 3, for example, is linked to the development of steatosis. In a recent study of co-infected IDUs, genotype 1 was associated with faster HIV disease progression and immunological decline, while genotype 4 was linked to slower progression. Because HCV genotype is such a strong predictor of response to treatment, some experts recommend getting a genotype test before commencing treatment.