An infection is when foreign organisms like bacteria, viruses, fungus or parasites take over an organ or another part of the body. In an infection, the infecting organism uses the organ's resources interfering with normal organ functioning. The infected organ swells and becomes irritated or sore. Minor infections remain in a particular organ while major infections can affect the whole body. Examples of infections are urinary tract infections(UTIs) and sexually transmitted infections (STIs).
Attribution: Straight Talk Foundation