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(Bacillary Dysentery; Shigella)


Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Feb 2020| Content last modified Feb 2020
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Shigellosis is infection by the gram-negative bacteria Shigella. It results in watery diarrhea or dysentery (the frequent and often painful passage of small amounts of stool that contains blood, pus, and mucus).

  • Shigella bacteria are excreted in stool and can be easily spread when hygiene or sanitation is inadequate.

  • People may have watery diarrhea, sometimes leading to severe dehydration.

  • Identifying the bacteria in a sample of stool can confirm the diagnosis.

  • For people with shigellosis and people who care for them, meticulous hygiene is necessary to avoid spreading the infection.

  • Fluids are given by mouth or, if the infection is severe, intravenously.

  • Antibiotics are used for people who have a severe infection or those who have a weakened immune system.

(See also Overview of Bacteria.)

Shigella bacteria are a common cause of dysentery in the United States and throughout the world.

Because stomach acid does not easily destroy these bacteria, ingesting even a small number of them causes infection. In the large intestine, the bacteria cause inflammation, and because they are then excreted in stool,

  • Infection spreads easily from person to person when hands are soiled.

Infection is also spread through the following:

  • Oral-anal sex

  • Food contaminated by infected food handlers who do not wash their hands with soap after using a toilet

  • Water contaminated with human waste

  • Swimming and wading pools that are inadequately chlorinated

Infection easily spreads among people who live together. Outbreaks also occur in places that are overcrowded and have inadequate sanitation, such as

  • Day-care centers for children

  • Long-term care facilities

  • Refugee camps

  • Institutions for the intellectually disabled

  • Cruise ships

  • Military camps

  • Developing countries

Children are more likely to become infected and to have severe symptoms, such as seizures.

There are four species of Shigella. All cause diarrhea. However, one—Shigella dysenteriae—is more likely to cause severe diarrhea, dysentery, and complications.


Mild infections cause low-grade fever (about 100.4 to 102° F [38 to 38.9° C]) and watery diarrhea 1 to 4 days after people ingest the bacteria. Some adults do not have a fever. Mild infections in adults usually resolve in 4 to 8 days.

In adults, the first symptoms may be painful abdominal cramps and a frequent urge to defecate. Passing stool may temporarily relieve the pain. These symptoms may become more severe and occur more frequently as the infection progresses.

Severe infections may cause low-grade or moderate fever and watery diarrhea that progresses to dysentery. In dysentery, bowel movements are frequent and contain blood, pus, and mucus. Severe infections usually resolve in 3 to 6 weeks.

In young children, symptoms begin suddenly. Symptoms include fever, irritability or drowsiness, loss of appetite, nausea or vomiting, diarrhea, and abdominal pain. Children may frequently feel an urgent need to defecate. Within 3 days, blood, pus, and mucus appear in stool. Unless complications develop, symptoms usually resolve by the second week.

Complications of shigellosis

Children, particularly young children, are most likely to have severe complications:

  • High fever (up to 106° F [41° C]), sometimes with delirium, seizures, or coma

  • Severe dehydration with weight loss

  • 20 or more bowel movements a day

  • With severe diarrhea, protrusion of part of the rectum out of the body (rectal prolapse)

  • Rarely, marked swelling of the intestine and tearing (perforation) of the large intestine

  • Hemolytic-uremic syndrome if the infection is due to Shigella dysenteriae type 1 (which is rare in the United States)

Severe dehydration can lead to shock and death, mainly in children under 2 years, in chronically ill, malnourished, or debilitated adults, and in older people.

In hemolytic-uremic syndrome, red blood cells are destroyed, causing anemia with fatigue, weakness, and light-headedness. Blood clots abnormally, causing the kidneys to stop functioning. Seizures or strokes can also occur.

Some adults develop reactive arthritis (inflammation of the joints). Inflammation of the eyes (uveitis) and urethra (causing painful urination) may occur weeks to months after the diarrhea.


  • Culture of a stool sample

A doctor suspects shigellosis based on the typical symptoms of pain, fever, and watery or bloody diarrhea in people who are likely to have been exposed to the bacteria.

To confirm the diagnosis of shigellosis, doctors take a sample of stool and send it to a laboratory to grow (culture) and identify the bacteria.

Bacteria are also tested to see which antibiotics are effective (a process called susceptibility testing).


Prevention includes the following:

  • Infected people should not prepare food for others.

  • After using the toilet, infected people should wash their hands, and someone should clean and disinfect the toilet before it is used again.

  • People caring for people with shigellosis should wash their hands with soap and water, particularly before they touch other people or handle food.

  • Infected children with symptoms should not have contact with uninfected children.

  • Diapers of infected children should be disposed of in a sealed garbage can, and the area used to change diapers should be wiped with disinfectant after each use.

  • Stool that contaminates clothing and bedclothes of infected people should be flushed away in running water, and the soiled clothing and bedclothes should be washed in a washing machine using the hot water cycle. When finished, surfaces of the sink, toilet, and washing machine should be wiped down with a disinfectant, such as diluted chlorine bleach.

Currently, no vaccine is available, but one is being studied.


  • Fluids containing salt

  • For severe infections, antibiotics

Water and salts lost because of diarrhea are replaced with fluids given by mouth or, if the infection is serious, by vein.

Mild infections typically resolve within 4 to 8 days. Antibiotics are not routinely required for healthy adults with mild infection.

However, doctors often give antibiotics to certain people, including those who

  • Are very young or very old

  • Have a weakened immune system

  • Have a moderate to severe infection

Severe infections may also require hospitalization so that fluids containing salts can be given intravenously and complications, such as hemolytic-uremic syndrome, can be treated. Antibiotics, such as azithromycin, ciprofloxacin (for adults), or ceftriaxone, are given.

Drugs to stop diarrhea (such as diphenoxylate or loperamide) may prolong the infection and should not be used.

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