Infectious arthritis is joint pain, soreness, stiffness and swelling caused by an infectious agent such as 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
Once the infection reaches the joint, it can cause symptoms of joint inflammation that is often accompanied by fever and chills. Depending on the type of infection, one or more joints may be affected.
The most common joint affected by bacterial infection is the knee. Small joints, such as those in fingers and toes, are more likely to become infected after a viral infection or after 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 (formerly called Reiter's disease), which appears to be caused by the immune system reacting to bacteria, rather than by the infection itself. In reactive arthritis, joint inflammation develops weeks, months or even years after the infection. Reactive arthritis happens most commonly after infections of the genital and gastrointestinal tracts.