Shigella were discovered more than 100 years ago by Japanese scientist Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by this bacteria. The group includes Shigella sonnei (group D Shigella) that account for more than two-thirds of the shigellosis in the United States. A second type, S. flexneri (group B Shigella), accounts for almost all of the rest. Other types of Shigella are rare in the United States, though they continue to be important causes of disease in the developing world.
The bacteria are found in milk and dairy products, poultry, and mixed salads, although they can develop in any moist food that is not thoroughly cooked. The bacteria multiply rapidly at or above room temperature. A person gets sick after ingesting bacteria, and it only takes a few organisms to cause illness. The bacteria also may be found in contaminated bodies of water, or in food that has been left out in the open where flies can contaminate it. Dogs who eat infected human feces can spread the infection to humans (especially children), and the disease also can be spread sexually with anal-oral contact.
Symptoms usually appear eight hours to eight days after ingestion, beginning with nausea and vomiting, water or bloody explosive diarrhea and stomach cramps, weakness, vision problems, headache, and problems swallowing. Young children and those with weakened immune systems may have more serious diarrhea and may take longer to recover. Those children who are already malnourished or weak will be much sicker.
The infection can be diagnosed by culturing the stool, which will reveal the type of bacteria.
Most children with the infection will recover on their own; some may need fluids to prevent dehydration. To treat severe cases, antibiotics will help stop the diarrhea, although Shigella has become resistant to some drugs. Antidiarrheal medications should not be given. Diluted drinks high in sugar and bland foods high in carbohydrates are tolerated best by the patient.
Confirmed cases must be reported to the health department, which will begin an investigation and control measures to prevent large-scale outbreaks. Although several vaccines have been tested, none has yet been licensed for use in preventing the disease. The single most important way to prevent the spread of this infection is to carefully wash hands after using the toilet, since Shigella is passed in feces.