What Is It?

Shigellosis is an infection of the colon (large intestine) caused by Shigella bacteria. Shigellosis sometimes is called bacillary dysentery because it can produce severe, even fatal, diarrhea. However, most cases of shigellosis are not life-threatening, and the infection often causes only mild symptoms.

Shigella bacteria are related to the E. coli bacteria that commonly live in the human digestive tract. They can be found in water that has been polluted with infected sewage, and they commonly enter the body through a contaminated drinking supply. Shigella bacteria also can be carried on food that has been rinsed with unclean water, grown in fields contaminated with sewage, or touched by flies that have touched feces. Especially among children, Shigella bacteria can be carried to the mouth on dirty fingers that have touched items soiled with feces, including dirty diapers, toilets and bathroom fixtures. Outbreaks of shigellosis are most common in areas where sanitation is poor, and in places where people live under confined or crowded conditions. This means Shigella is a common cause of outbreaks of diarrhea in day-care centers, military installations, institutions and cruise ships. Shigella also can be passed from person to person during anal-oral sex.

Worldwide, approximately 140 million people develop shigellosis each year, and about 600,000 die. Most of these deaths occur in developing countries among children under age 5. In the United States, only about 25,000 to 30,000 cases occur each year, primarily among children ages 1 to 4. Children of this age are especially at risk for shigellosis because they are starting to use the toilet and often forget the basics of good hygiene. Infants are also at the highest risk of becoming seriously ill from a Shigella infection.


Although health experts do not know why, some people are able to take in Shigella bacteria without becoming ill. Others develop only a brief fever, or a brief fever together with mild diarrhea that goes away on its own. About 25 percent of patients, however, develop high fever, abdominal cramping and severe, watery diarrhea that can contain blood, mucus and pus. These patients can have 10 to 30 bowel movements each day, together with a persistent urge to have a bowel movement that can lead to rectal prolapse (an abnormal protrusion of the rectum). Rarely, Shigella bacteria can affect other parts of the body that are far from the digestive tract. When this happens, there can be seizures, confusion or coma, kidney failure, arthritis, rashes or other symptoms.


Your doctor will ask you about your symptoms and about the appearance of your bowel movements. He or she also will ask you about recent travel to developing countries, contact with people who have severe diarrhea, and possible exposure to contaminated pools or lakes, or food.

Your doctor will diagnose shigellosis based on a physical examination and the results of laboratory tests. These tests include taking a swab of your rectum or a sample of your stool to be checked in the laboratory for Shigella bacteria. If you have signs of dehydration (excessive loss of body water) or significant blood loss, additional blood tests may be necessary.

Expected Duration

In most otherwise healthy people with mild shigellosis, diarrhea goes away on its own within five to seven days. However, in very young children, the elderly, or people with chronic illnesses, shigellosis can be severe and can lead to life-threatening dehydration and other complications within a few days.


There is no vaccine to protect against shigellosis. To prevent the spread of Shigella bacteria, you should:

  • Practice good hygiene, especially frequent handwashing.
  • Wash your hands immediately after changing a child’s diaper, especially if the child has diarrhea.
  • Dispose of soiled diapers in closed-lid garbage cans.
  • Swim only in lakes and pools whose water quality is monitored by local health officials.
  • Follow precautions when traveling to developing countries, such as drinking only treated or boiled water, and eating only foods that have been cooked thoroughly. Never eat unpeeled fruits, and always peel fruits yourself immediately before eating them.


If you have a mild case of shigellosis, your doctor probably will choose not to treat you with antibiotics since your symptoms probably will go away on their own even before the results of your stool cultures are available. Sometimes antibiotics are given anyway if there are very young or very old members in a household who could acquire the infection.

If you have a severe case of shigellosis, your doctor will prescribe fluids to treat dehydration and will choose an antibiotic based on the circumstances in which you acquired your infection. For example, if you acquired shigellosis in the United States, your infection probably will respond to common antibiotics such as ampicillin (Polycillin, Totacillin, Omnipen), trimethoprim-sulfamethoxazole (Bactrim, Septra and other brand names), tetracycline (sold under many brand names), or ciprofloxacin (Cipro). However, if you acquired your infection during travel to a developing country, the infecting strain of Shigella is more likely to be resistant to these common antibiotics, and a newer or less commonplace antibiotic may be needed.

Most experts recommend against using antidiarrheal medications that slow the bowel movements of shigellosis because of a concern that such medications can make the illness worse. However, a few medical studies have shown that these medications may be used safely to treat symptoms.

When To Call A Professional

Call your doctor if you develop severe diarrhea, especially if the bowel movements contain blood or mucus. Also, call your doctor whenever you have a fever and severe diarrhea and you have signs of dehydration, including very dry mouth and lips, dry skin, sunken eyes, severe thirst and a rapid pulse.


In industrialized countries, most people with shigellosis recover completely. However, in about 3 percent of people infected with a type of Shigella called Shigella flexneri, Reiter’s syndrome develops. This syndrome causes joint pain, eye irritation and urinary discomfort.

Johns Hopkins patient information

Last revised:

Diseases and Conditions Center

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.