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. Because milder cases are not diagnosed or reported, the actual number of infections may be several times greater. Since children at this age often have poor handwashing practices, many cases are related to illness within child care centers and spread of illness within families of small children. Outbreaks can also be foodborne, as when an unhygienic foodhandler or sewage contaminates food, or they can occur in crowded conditions where personal hygiene is poor, such as jails and mental institutions.