Infectious Arthritis

Infectious arthritis (septic arthritis) is a serious disorder in which affected joints are inflamed because of infection. Fluid then accumulates in the inflamed joint.

The risk of developing infectious arthritis increases with age. Risk is also greater for people whose immune system is impaired because of cancer, diabetes, or treatment with drugs such as corticosteroids.

Causes

Among older people, bacteria are almost always the cause of the infection. Bacteria usually get directly into the joint as a result of injury or surgery. Alternatively, bacteria travel from a nearby infection in the body or through the bloodstream from a more distant site. Sometimes the source of the bacteria is unknown. Infectious arthritis most often affects joints already damaged by disease, usually osteoarthritis or RA.

Symptoms and Diagnosis

Infectious arthritis usually begins with the sudden onset of fever, a general sick feeling, and pain in one or more joints. Primarily the large joints are affected, most commonly the shoulders, elbows, wrists, hips, and knees. The affected joint is often red, warm, and swollen. However, some people with infectious arthritis look and feel as they normally do, except that they may have a slight fever.

A doctor diagnoses infectious arthritis by examining the affected joint and removing fluid from it. Analysis of the fluid may show a high white blood cell count, which indicates infection. The bacteria causing the infection may also be identified in the sample. Blood samples are also obtained to determine whether the bacteria traveled from the bloodstream.

Treatment

Immediate treatment with antibiotics given intravenously and removal of joint fluid (aspiration) is needed to avoid permanent damage to the joint and to the cartilage inside the joint. Joint fluid is drawn out as completely as possible to help speed the body's ability to clear the infection. This procedure is repeated daily until the white blood cell count in the joint fluid decreases. Antibiotics given intravenously are later switched to antibiotics taken by mouth. If fever and joint pain are not substantially reduced in 48 to 72 hours, joint fluid may be surgically removed (surgical drainage).