Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pneumonia ?
    ### Response:
    Pneumonia is an infection in one or both of the lungs. Many germs, such as bacteria, viruses, and fungi, can cause pneumonia. You can also get pneumonia by inhaling a liquid or chemical. People most at risk are older than 65 or younger than 2 years of age, or already have health problems.
    