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Micrograph of Shigella sonnei bacteria
Gram-negative Shigella sonnei bacteria.
Credit: CDC, Dr.Todd Parker

Shigellosis is an intestinal infectious disease that is spread primarily through consumption of contaminated food and water. Transmission also can occur via person-to-person contact or by handling contaminated surfaces. Estimates on the number of shigellosis cases vary, as many mild cases often are not diagnosed or reported. A study of major pathogens that caused foodborne disease in the United States, mostly from 2000-2008, estimated that approximately 131,000 episodes of acquired foodborne infection with Shigella occurred each year, with 20 percent of these patients requiring hospitalization.


Shigellosis is caused by Shigella bacteria. There are four groups of Shigella that cause infection in humans: Shigella sonnei, S. dysenteriae, S. flexneri, and S. boydii. S. sonnei is the most common type of Shigella in developed countries, including the United States. Outbreaks of shigellosis frequently occur in tropical or temperate climates, especially in areas with severe crowding or poor hygiene. Outbreaks sometimes occur in daycare and institutional settings.


You can be infected with Shigella by

  • Eating food or drinking beverages contaminated by food handlers infected with Shigella who did not wash their hands properly after using the bathroom
  • Eating vegetables grown in fields containing contaminated sewage
  • Eating food contaminated by flies that bred in or contacted infected feces
  • Drinking or swimming in contaminated water

Ingestion of an extremely low number of bacteria, 10 to 100, can cause infection. If you are infected with Shigella, you can still pass the bacteria to others even if you have no symptoms of shigellosis. Toddlers and small children under the age of five are at highest risk for infection with shigellosis; many cases are spread in child daycare settings or among families with small children.

If you know you have shigellosis, you should not prepare food or beverages for others until laboratory tests show that you no longer carry Shigella bacteria.


Symptoms of shigellosis include

  • Fever
  • Tiredness
  • Watery or bloody diarrhea
  • Nausea and vomiting
  • Abdominal pain

Symptoms usually begin within 2 days after you come in contact with Shigella. You usually get better within 5 to 7 days.


Laboratory tests can identify the presence of Shigella in your stool if you are infected. The laboratory can also do special tests to tell which type of Shigella you have and which antibiotics, if any, would be best to treat it.

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If you have a mild infection, you should get better quickly without taking medicine. If you need to be treated, your healthcare provider usually will prescribe an antibiotic such as ampicillin or ciprofloxacin. Antidiarrheal medicines may make the illness worse because they do stop the diarrhea, but do not kill the bacteria in your intestine.


To prevent getting shigellosis you should

  • Wash your hands with soap and water before preparing foods and beverages
  • Wash your hands after using the bathroom or changing infant diapers
  • Disinfect diaper-changing areas after use
  • Help young children wash their hands carefully after they use the bathroom
  • Avoid swallowing swimming pool water


People who have symptoms of diarrhea usually recover completely, although their bowel habits may not return to normal until several months later.

Hemolytic Uremic Syndrome

S. dysenteriae type 1 bacteria produce Shiga toxin (poison), which can severely damage the lining of your intestines and kidneys. This toxin can cause life-threatening hemolytic uremic syndrome (HUS), which can lead to kidney failure. In North America, HUS is the most common cause of acute kidney failure in children, who are particularly prone to this complication. This condition is usually treated in an intensive care unit of a hospital, sometimes with blood transfusions and kidney dialysis.

About 8 percent of people with HUS have other lifelong complications, such as high blood pressure, seizures, blindness, paralysis, and the effects of having part of their intestines removed due to the disease.

Reiter's Syndrome

S. flexneri infection can progress to Reiter’s syndrome, which can last for months or years and can lead to chronic arthritis. Its symptoms are painful joints, irritated eyes, and painful urination.

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Basic research helps scientists better understand how food- and water-borne microbes cause disease in humans.

NIAID supports research to study how bacterial pathogens (germs) cause disease when they infect, colonize, and then interact with the human host's body. For example, scientists have discovered that some bacteria can recognize that they are inside the intestinal tract and then activate an important set of their genes that enable them to live in the body and cause disease. Other NIAID-sponsored research focuses on how the organism grows and interacts inside the human cell. Scientists have identified genes that permit Shigella to obtain iron, an essential nutrient, from the human body. In addition, scientists have identified genes that appear to be involved in signaling certain immune system cells to cause inflammation, which may contribute to the development of diarrhea. Investigators are further defining the ways by which the toxins produced by Shigella result in the kidney damage leading to hemolytic uremic syndrome (HUS), a life-threatening condition. The primary goal of this research is to better understand how this kidney disease progresses. Future studies like these might define new ways to intervene, whether by prevention or treatment, in the disease process.

Recently, scientists have determined the complete genome sequences (genetic blueprint) for Shigella flexneri, as well as other major enteric bacteria. Scientists hope that sequencing information will speed the discovery of new targets for treatments and vaccines against foodborne pathogens.

NIAID-supported researchers are investigating small molecules that inhibit bacterial components that are critical for the development of shigellosis; these small molecules act through novel mechanisms that hopefully will not lead to the emergence of drug resistance that can occur with the use of antibiotics. Small molecules currently under study act to limit damage to the intestine, to prevent bacteria from obtaining essential nutrients, and to prevent the transport of bacterial proteins to the bacterial cell surface where they interact with the host cell in a variety of ways to cause disease.

Researchers are developing vaccines to prevent Shigella infections in humans. Scientists also are developing and testing monoclonal antibodies to combat the effects of Shiga toxin. These and other clinical studies are geared towards protecting the public from this diarrheal disease and towards improving the general public health.

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Last Updated September 15, 2015