Reactive arthritis (ReA) is a rare type of arthritis that can affect joints of the lower body such as the feet, ankles, hips, knees and sometimes the lower back. It occurs after certain types of infections. Reactive arthritis is usually acute (sudden onset, short-term), but it can also be chronic (long-term). Chronic forms can flare up and down. ReA used to be called Reiter’s syndrome.
Reactive arthritis typically occurs 10 to 14 days after an infection of the bowels (diarrhea), the urinary tract, or following a sexually transmitted infection (STI) such as chlamydia. For some reason that is not well understood, the infection triggers an arthritic reaction.
ReA belongs to a family of diseases called the seronegative spondyloarthropathies. Other members of this family include ankylosing spondylitis, psoriatic arthritis, and enteropathic arthritis.
Reactive arthritis affects adult men and women aged 30 to 40. It is a bit more common in men. There is a genetic component in people who get ReA. About 75% of all patients who get it have a gene called HLA-B27.