Reactive arthritis is a rare disease that causes inflammation of the joints and, in many cases, other areas, particularly the urinary tract and eyes. It is triggered by an infection, usually by a sexually transmitted organism or by certain gastrointestinal bacteria.
The most common infection causing reactive arthritis is the sexually transmitted disease (STD) chlamydia. Reactive arthritis can also be caused by gastrointestinal infection from bacteria such as salmonella, shigella, campylobacter or Yersinia, infections that can cause diarrhea and vomiting. These bacteria often are found in contaminated food or water. While these infections are common, reactive arthritis is not. Scientists believe that people who develop reactive arthritis have a certain genetic makeup. Supporting the theory that genetic makeup is a risk factor, about 50% of people with reactive arthritis carry a gene called HLA-B27, compared with 8% of the general population.
Reactive arthritis is thought to be an autoimmune disorder, which means the body's immune system mistakenly attacks its own tissues. In this case, the immune system is jolted into action by the infection but continues attacking after the infection is gone.
Reactive arthritis typically includes arthritis, eye inflammation (conjunctivitis or uveitis) and inflammation of the urethra (urethritis). However, some people develop only one or two of these. Reactive arthritis is most common in people between the ages of 20 and 40, with a prevalence of about 0.03% (30 per 100,000).