Shigella are Gram-positive, nonmotile, nonsporeforming rod-shaped bacteria. Shigella bateria were discovered over 100 years ago by a Japanese scientist named Shiga, for whom they are named. Currently, Shigella (shigellosis) accounts for approximately 10% of reported food-borne illness in the United States. There are several different kinds of Shigella that cause illness: Shigella sonnei, known as "Group D" Shigella, accounts for over two-thirds of shigellosis in the United States. In turn, Shigella flexneri, or "group B" Shigella, accounts for the majority of the rest. Other types of Shigella are rare in this country, though they continue to be important causes of disease in the developing world. One type found in the developing world, Shigella dysenteriae type 1, can cause deadly epidemics.
In addition to person to person transmission (through the fecal-oral route), Shigella may also be acquired from eating contaminated food, or by drinking or swimming in contaminated water. Incriminting foods have included salads (potato, tuna, shrimp, macaroni, and chicken), raw vegetables, milk and dairy products, and poultry.
Shigella are highly infectious, and a relatively small number of organisms can cause illness. In turn, illness is caused when Shigella organisms are consumed and then attach to and penetrate the epithelial cells of the intestinal mucosa. After invasion, the bacteria multiply and spread to contiguous cells resulting in tissue destruction. Some strains produce enterotoxin and Shiga toxin (similar to the verotoxin of E. Coli O157:H7). Symptoms include abdominal pain, cramps, diarrhea, fever, vomiting and/or blood or mucus in stools. Symptoms typically occur between 36 and 48 hours after the consumption of contaminated food, and will typically resolve within 4 to 7 days.
As with other common food-borne pathogens, the spread of Shigella can be prevented by frequent and careful handwashing with soap.