Is incest big issue in us?:
Well, first off, incest is not always "child abuse."  Sex between closely related CONSENTING adults probably happens.  

In the USA, incest is not common. There is a stereotype about the south, that it happens there a lot. This is untrue.  In fact, the highest rates of incest in the USA are found in among hispanics. 

Furthermore, incest is RAMPANT in Central and South America.  

Love Jack