Co-infections or super-infections with a non-hepatitis virus are also possible, and for HIV population, it is quite common due to the similarities of the infection route. (About 40% of patients with HIV are co-infected with HCV.) For these conditions, the clinical symptoms and disease courses are usually more complex and serious than a single viral infection case. Although super or co-infections can make the disease more severe and its progression faster, there is also the possibility that one of the agents, such as HCV, could help promote the clearings of the other virus, such as HBV, from the body. HCV could also take over the position of HBV and become the major virus to cause persistent chronic infection.