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The specific arrangement of genetic material within a virus is called the genotype. There are six main genotypes of the hepatitis C virus. Of the different genotypes, genotype 1 is the type most commonly found in the United States. Between 70 to 90 percent of Americans with hepatitis C have this genotype. Knowing which of the genotypes a person has is important because the genotype can affect the success of the treatment and determine how long the medications need to be taken.
Just as there are different types of hepatitis viruses, there are also a few different types of the hepatitis C virus itself. Though they all cause hepatitis C, each type of the virus has a slightly different arrangement of its genetic material, in this case called RNA. The specific arrangement of the RNA is called the genotype.
The main hepatitis C genotypes (also known as "subtypes") are known simply as:
- Genotype 1
- Genotype 2
- Genotype 3
- Genotype 4
- Genotype 5
- Genotype 6.
Of the different genotypes of hepatitis C, genotype 1 is the type most commonly found in the United States. Between 70 to 90 percent of Americans with hepatitis C have this genotype.
Hepatitis C virus genotypes 2 and 3 are less common. Only 10 to 20 percent of infected people in the U.S. have either of these genotypes.
The hepatitis C genotype matters because it can affect which medications are chosen, how successful a person's hepatitis C treatment will likely be, and how long the hepatitis C medication will need to be taken.
For example, it is estimated that up to 50 percent of the people with genotype 1 will have a sustained response, or successful treatment, with peginterferon and ribavirin. Patients with genotypes 2 and 3 are almost three times more likely than patients with genotype 1 to respond to therapy with alpha interferon or the combination of alpha interferon and ribavirin. Because of the poorer response in people with genotype 1, adding a third type of medication (a hepatitis C protease inhibitor or nucleotide analog NS5B polymerase inhibitor) is usually recommended.
Furthermore, when using combination therapy, the recommended treatment length depends on the genotype. Depending on the genotype and the treatment regimen, treatment may be as short as 12 weeks or as long as 48 weeks.
For these reasons, testing for the genotype of hepatitis C is often helpful. Once the genotype is identified, it does not need to be tested again -- hepatitis C genotypes do not change during the course of infection. There are other factors that can also affect your chances of having a successful treatment, so be sure to discuss your individual situation with your healthcare provider.