Reactive arthritis (Reiter's syndrome)

Reactive arthritis is a form of joint inflammation triggered by an infection elsewhere in the body, often in the gut, urinary tract, or genital tract, where the immune response set off by the infection is thought to end up inflaming the joints, sometimes through bacterial antigens or genetic material detected within the joint itself. It usually begins days to weeks after the triggering infection and most often affects the lower-extremity joints, and in many people it settles over months, though it can recur or become chronic. Reactive arthritis is considered part of the broader spondyloarthritis family and is strongly associated with the HLA-B27 gene.

Research describes a worldwide prevalence estimated around 40 per 100,000 people, and certain triggering infections such as Campylobacter are estimated to lead to reactive arthritis in roughly 1 to 5 percent of those infected.

Common signs

Joint pain and swelling, often in the knees, ankles, and feet, frequently on one side, along with attachment-point pain such as heel pain. Some people also have eye irritation (conjunctivitis), urinary symptoms, or skin and mouth changes.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.