Recognized worldwide as the most common cause of dysentery, the Shiga bacillus—or Shigella—is a gram-negative rod belonging to the family Enterobacteriaceae, so named because many of its members live in the intestines of humans and warm-blooded animals. 

Shigellosis is the clinical syndrome caused by Shigella species and is most typically associated with diarrhea and other gastrointestinal symptoms. Shigella species are transmitted by the fecal-oral route, and most infections are transmitted from person to person, reflecting the low infectious dose. Because of its quite common person-to-person spread, shigellosis has long been associated with outbreaks in daycare centers, nursing homes, institutional settings (e.g., prisons), and cruise ships. Shigella infections also may be acquired from eating contaminated food; studies estimate that approximately one-third of U.S. shigellosis cases annually might be caused by the consumption of contaminated food. 

Most people who are infected with Shigella develop diarrhea, fever, and stomach cramps after being exposed to the bacteria. Symptoms may start 12 to 96 hours after exposure, usually within one to three days. Reactive arthritis can develop after a Salmonella infection. The other relatively rare complication that can occur with a Shigella infection is the development of hemolytic uremic syndrome (HUS). This rare complication is more commonly caused by E. coli O157:H7, and it can lead to a low red blood cell count (hemolytic anemia), low platelet count (thrombocytopenia), and acute kidney failure. It is more common to develop HUS after being infected with S. dysenteriae.