Shigellosis usually resolves in five to seven days but can last for weeks. Shigellosis is transmitted strictly by human feces. Unlike several other gastrointestinal agents, no animal reservoir is known. Shigellosis is extremely infectious, as only 10-100 organisms are necessary to cause infection. Other routes of transmission include ingestion of contaminated food or water, homosexual activity, and contact with a contaminated, inanimate object.
Houseflies are also vectors, physically transporting infected feces.
Infection can be transmitted during the acute illness until bacteria are no longer shed, usually within four weeks after onset. The infection is diagnosed most commonly by stool culture. Antimicrobial therapy is effective in shortening the duration of illness and reducing carriage rate. Reiter's syndrome is caused by a reaction to this Shigella infection, and occurs only in those genetically predisposed to it. Each year , about 18,000 cases of shigellosis are reported nationwide.