Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Gastroenteritis ?
    ### Response:
    Have you ever had the "stomach flu?" What you probably had was gastroenteritis - not a type of flu at all. Gastroenteritis is an inflammation of the lining of the intestines caused by a virus, bacteria or parasites. Viral gastroenteritis is the second most common illness in the U.
    