Formerly known as Reiter syndrome, reactive arthritis (ReA) is joint inflammation that occurs after a bacterial infection originating outside the joints (i.e., “extra-articular”). These infections are either gastrointestinal (e.g., SalmonellaCampylobacterYersiniaShigella, and sometimes E. coli) or urogenital (most commonly Chlamydia trachomatis, but also Neisseria gonorrhea and Mycoplasma). Acute ReA occurs several days or weeks after the antecedent infection. It is typically monoarticular (involving one joint) or oligoarticular (involving just a few joints, usually less than six). The lower extremities are most commonly involved, but it can also involve the arms and spine. Other names for ReA are post-infectious arthritis, post-dysenteric arthritis, and seronegative arthritis. When it lasts more than six months, it is called chronic reactive arthritis.

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