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Shigellosis is an infectious disease caused by a group of bacteria called Shigella. Every year, about 14,000 cases of shigellosis are reported in the United States. Because many milder cases are not diagnosed or reported, the actual number of infections may be twenty times greater. In the developing world, shigellosis is far more common and is present in most communities most of the time.
The Shigella bacteria pass from one infected person to the next. Shigella are present in the diarrheal stools of infected persons while they are sick and for up to a week or two afterwards. Most Shigella infections are the result of the bacterium passing from stools or soiled fingers of one person to the mouth of another person. This happens when basic hygiene and handwashing habits are inadequate and can happen during certain types of sexual activity. It is particularly likely to occur among toddlers who are not fully toilet-trained. Family members and playmates of such children are at high risk of becoming infected.
Shigella infections may be acquired from eating contaminated food. Contaminated food usually looks and smells normal. Food may become contaminated by infected food handlers who forget to wash their hands with soap after using the bathroom. Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected feces and then contaminate food. Water may become contaminated with Shigella bacteria if sewage runs into it, or if someone with shigellosis swims in or plays with it (especially in splash tables, untreated wading pools, or shallow play fountains used by daycare centers). Shigella infections can then be acquired by drinking, swimming in, or playing with the contaminated water. Outbreaks of shigellosis have also occurred among men who have sex with men.
Most who are infected with Shigella develop diarrhea, fever, and stomach cramps starting a day or two after they are exposed to the bacteria. The diarrhea is often bloody. Shigellosis usually resolves in 5 to 7 days. Persons with shigellosis in the United States rarely require hospitalization. A severe infection with high fever may be associated with seizures in children less than 2 years old. Some persons who are infected may have no symptoms at all, but may still pass the Shigella bacteria to others.
Many different kinds of germs can cause diarrhea, so establishing the cause will help guide treatment. Determining that Shigella is the cause of the illness depends on laboratory tests that identify Shigella in the stools of an infected person. The laboratory can also do special tests to determine which antibiotics, if any, would be best to treat the infection.
Persons with mild infections usually recover quickly without antibiotic treatment. However, appropriate antibiotic treatment kills Shigella bacteria, and may shorten the illness by a few days. The antibiotics commonly used for treatment are ampicillin, trimethoprim/sulfamethoxazole (also known as Bactrim or Septra), ceftriaxone (Rocephin), or, among adults, ciprofloxacin. Some Shigella bacteria have become resistant to antibiotics. This means some antibiotics might not be effective for treatment. Using antibiotics to treat shigellosis can sometimes make the germs more resistant. Therefore, when many persons in a community are affected by shigellosis, antibiotics are sometimes used to treat only the most severe cases. Antidiarrheal agents such as loperamide (Imodium) or diphenoxylate with atropine (Lomotil) can make the illness worse and should be avoided.
Currently, there is no vaccine to prevent shigellosis. However, the spread of Shigella from an infected person to other persons can be stopped by frequent and careful handwashing with soap.