Reactive or infection-associated arthritis is a type of spondyloarthropathy brought on by infection. Reiter's syndrome is a special case of infection-associated arthritis with a particular set of systems (discussed later). Affected children are often very ill, with fever, rash, and arthritis. Sometimes the arthritis is in only one large joint, but at other times it may be widespread, affecting many joints both large and small. It was originally termed "reactive arthritis" because the arthritis frequently begins shortly after a significant viral or bacterial infection. The name was changed to infection-associated arthritis to remind physicians that in some cases the infection is still present and may require treatment.
The most common infectious agents that cause these forms of arthritis are bacteria (shigella, salmonella, neisseria, and chlamydia) and viruses (especially parvovirus B19). The arthritis associated with Lyme disease is also a form of infection-associated arthritis. Mild and brief arthritis following a variety of infections is very common. Once the episode has passed, most children recover completely. A typical episode of infection-associated arthritis resolves in three to six weeks. However, some children develop arthritis that lasts for a longer period. If the arthritis persists for a year or more, then it is considered arthritis that was initiated by an infection, but it is no longer considered reactive or infection-associated arthritis.
Although many children with infection-associated arthritis look very ill at the beginning, the majority of children recover completely. Some are initially misdiagnosed as having systemic-onset arthritis, but the fever pattern and rash of reactive arthritis and systemic-onset arthritis are different. Recurrences of reactive arthritis are rare (if the underlying infection has resolved), but there are children with a substantial genetic predisposition to arthritis who develop repeated episodes of arthritis following exposure to different infectious agents.
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