What Is It?

Infectious arthritis is joint pain, soreness, stiffness and swelling caused by an infection by bacteria, viruses or fungi.

These infections can enter a joint various ways:

• After spreading through the bloodstream from another part of the body, such as the lungs during pneumonia

• Through a nearby wound

• After surgery, an injection or trauma, such as an insect bite

Once the infection 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. In people who use intravenous drugs, joints in the spine or breastbone (sternum) may be involved. People who already have rheumatoid arthritis or another joint disease are more likely to develop infectious arthritis.

Certain bacteria 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 the infection itself. In Reiter's disease, arthritis develops weeks, months or even years after the infection. Reiter's disease happens most commonly after infections of the genital and gastrointestinal tracts.

Symptoms

Symptoms of infectious arthritis include:

• Joint pain and stiffness, typically in the knee, shoulder, ankle, finger, wrist or hip

• Warmth and redness around the joint

• Fever and shaking chills

• Skin rash

Other symptoms vary, depending on the cause. Some 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.

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). Arthritis can develop in the later stages of Lyme disease.