Shigella is a bacterium that can cause sudden and severe diarrhea (gastroenteritis) in humans. Shigellosis is the name of the disease that Shigella causes. The illness is also known as "bacillary dysentery." Shigella bacteria can infect the intestinal tract after the ingestion of relatively few organisms. This is why shigellosis is the most communicable of the bacterial-induced diarrheas.
The source of Shigella bacteria is the excrement (feces) of an infected individual that is ultimately ingested by another person. The infectious material is spread to new cases by person-to-person contact or via contaminated food or water. Approximately 20% of the nearly 450,000 cases of shigellosis that occur annually in the U.S are foodborne-related. Generally, the food preparer is the individual who contaminates the food, but food may also become contaminated during processing. Contamination of drinking water by Shigella is a problem that more often occurs in the developing world, but swimming pools and beaches in the U.S. can become contaminated by infected individuals. No group of individuals is immune to shigellosis, but certain individuals are at increased risk, particularly small children. Persons infected with HIV experience shigellosis much more commonly than other individuals.