Infection describes the uncontrolled growth of a foreign living organism inside the human body. Infections can be caused by bacteria, a virus, or a parasite. The infection can occur in a discrete area (such as an abcess) or can be found throughout the body (as in sepsis).
The body usually responds to any type of infection with a fever unless the patient is immunocompromised. As many infections can only exist within a narrow range of temperatures, the fever does prevent the infection from spreading. However, fever can also damage normal body cells, and fevers of more than 105F(40C) are usually fatal. Pain and inflamation are also common symptoms.
Surgical patients, burn victims and immunocompromised patients are all vulnerable to infection. In a healthy person, the immune system can fight off most infections, either by not allowing the infection to enter the body, or by using histamines, white blood cells and antibodies to kill foreign cells. However, many infections take advantage of "holes" in the immune system. For example, most STD's take advantage of the fact that the reproductive system is partially isolated from the immune system. HIV and the plague attack the body's immune system cells directly.
The routine treatment for many types of infection is bed rest (to allow the immune system to take advantage of the body's resources) and liquids. Bacterial infections can be treated with antibiotics. Most other infections have to be treated with disease specific drugs.