Infectious Arthritis

What Is It?

Infectious arthritis is joint pain, soreness, stiffness and swelling caused by an infection by bacteria, viruses or fungi. These infections can affect a joint after spreading through the bloodstream from another part of the body, such as the lungs during pneumonia. An infection also can enter a joint through a nearby wound. Sometimes, tissue around the joint becomes infected after surgery, an injection or trauma, such as an insect bite. Once the infectious agent reaches the joint, it can cause symptoms of joint inflammation and, at times, fever and chills. Depending on the type of infection, one or more joints may be affected.

The most common joint affected by infection is the knee. Small joints, such as those in fingers and toes, are more likely to become infected after a viral infection or direct injury, such as a bite. Among intravenous drug users, joints such as those in the spine or sternum (breastbone) may be involved. People who already have rheumatoid arthritis or other joint disease are more likely to develop infectious arthritis.

Certain infectious agents can cause a form of infectious arthritis called reactive arthritis or Reiter's disease, which appears to be caused by the immune system reacting to bacteria, rather than by a direct infection of the joint. In this condition, arthritis develops weeks, months or even years after the infection. By the time the arthritis develops, the infection is gone. Infections of the genital and gastrointestinal tracts are the most common triggers of reactive arthritis.

Symptoms

Symptoms of infectious arthritis include:

• Joint pain and stiffness, typically in the knee, shoulder, ankle, finger, wrist or hip
• Warmth and redness in surrounding tissue
• Fever and shaking chills
• Skin rash

Other symptoms vary, depending on the cause. Some of the more common causes of infectious arthritis include:

Lyme disease
Lyme disease is caused by bacteria that live in deer ticks and are transmitted through a tick bite into a person's bloodstream. Arthritis can develop in the later stages of Lyme disease.

After an infected tick bites a person, a large, round, red rash (called erythema migrans) usually develops around the bite, often with an area of skin in the center that appears normal. Flulike symptoms sometimes develop, including fever, headaches, chills, body aches, stiffness, nausea, fatigue and sore throat. The symptoms of Lyme disease often mimic those of other diseases, and considerable time can pass between the appearance of the rash and the next wave of symptoms.

Because the tick bite often goes unnoticed and the rash may be overlooked, Lyme disease is not always diagnosed immediately. When the infection is not treated, further symptoms may develop, including joint inflammation (most commonly in the knee), neurologic symptoms (confusion, convulsions, muscle weakness), and an abnormally slow heart rate that may lead to fainting. Antibiotic treatment usually cures the illness.