Shigella infection (shigellosis) is an intestinal infection caused by a family of bacteria known as shigella. The main sign of shigella infection is diarrhea, which often is bloody.

Shigella is very contagious. People get infected with shigella when they come in contact with and swallow small amounts of bacteria from the stool of a person who is infected with shigella. For example, this can happen in a child care setting when staff members don't wash their hands well enough after changing diapers or helping toddlers with toilet training. Shigella bacteria can also be passed in infected food or by drinking or swimming in unsafe water.

Children under age 5 are most likely to get shigella infection, but it can occur at any age. A mild case usually clears up on its own within a week. When treatment is needed, doctors generally prescribe antibiotics.

Signs and symptoms of shigella infection usually begin a day or two after contact with shigella. But it may take up to a week to develop. Signs and symptoms may include:

• Diarrhea (often containing blood or mucus)
• Stomach pain or cramps
• Fever
• Nausea or vomiting

Symptoms generally last for about five to seven days. In some cases, symptoms may last longer. Some people have no symptoms after they've been infected with shigella. However, their feces may still be contagious up to a few weeks.

When to see a doctor

Contact your doctor or seek urgent care if you or your child has bloody diarrhea or diarrhea severe enough to cause weight loss and dehydration. Also, contact your doctor if you or your child has diarrhea and a fever of 101 F (38 C) or higher.

Infection occurs when you accidentally swallow shigella bacteria. This can happen when you:

• Touch your mouth. Direct person-to-person contact is the most common way the disease is spread. For example, if you don't wash your hands well after changing the diaper of a child who has shigella infection, you may become infected yourself.
• Eat contaminated food. Infected people who handle food can spread the bacteria to people who eat the food. Food can also become infected with shigella bacteria if it grows in a field that contains sewage.
• Swallow contaminated water. Water may become infected with shigella bacteria either from sewage or from a person with shigella infection swimming in it.

• Being a child. Children under age 5 are most likely to get shigella infection. But shigella can infect people of any age.
• Living in group housing or participating in group activities. Close contact with other people spreads the bacteria from person to person. Shigella outbreaks are more common in child care centers, community wading pools, nursing homes, jails and military barracks.
• Living or traveling in areas that lack sanitation. People who live or travel in developing countries are more likely to get shigella infection.
• Being a man who has sex with men. Men who have sex with men are at higher risk of shigella infection because of direct or indirect oral-anal contact during sexual activity.

Shigella infection usually clears up without complications. But it may take weeks or months before your bowel habits return to normal.

Complications may include:

• Dehydration. Constant diarrhea can cause dehydration. Signs and symptoms include lightheadedness, dizziness, lack of tears in children, sunken eyes and dry diapers. Severe dehydration can lead to shock and death.
• Seizures. Some children with a shigella infection have seizures. Seizures are more common in children who run a high fever, but can occur in children who do not have a high fever. It's not known whether the seizures are a result of the fever or the shigella infection itself. If your child has a seizure, contact your doctor immediately.
• Rectal prolapse. In this condition, straining during bowel movements or inflammation of the large intestine may cause the mucous membrane or lining of the rectum to move out through the anus.
• Hemolytic uremic syndrome. This rare complication of shigella, more commonly caused by a type of E. coli bacteria than by shigella bacteria, can lead to a low red blood cell count (hemolytic anemia), low platelet count (thrombocytopenia) and acute kidney failure.
• Toxic megacolon. This rare complication occurs when your colon becomes paralyzed, preventing you from having a bowel movement or passing gas. Signs and symptoms include stomach pain and swelling, fever and weakness. If you don't receive treatment for toxic megacolon, your colon may break open (rupture), causing peritonitis, a life-threatening infection requiring emergency surgery.
• Reactive arthritis. Reactive arthritis develops in response to an infection. Signs and symptoms include joint pain and inflammation, usually in the ankles, knees, feet and hips; redness, itching and discharge in one or both eyes (conjunctivitis); and painful urination (urethritis).
• Bloodstream infections (bacteremia). Shigella infection can damage the lining of the intestines. In rare cases, shigella bacteria can enter the bloodstream through the damaged intestinal lining and cause a bloodstream infection.

Although researchers continue to work to develop a shigella vaccine, nothing is available yet. To prevent the spread of shigella:

• Wash hands with soap and water for at least 20 seconds frequently
• Watch small children when they wash their hands
• Throw away soiled diapers properly
• Disinfect diaper-changing areas after use
• Don't prepare food for others if you have diarrhea
• Keep children with diarrhea home from child care, play groups or school
• Avoid swallowing water from ponds, lakes or untreated pools
• Avoid sexual activity with anyone who has diarrhea or who recently recovered from diarrhea
• Don't go swimming until you have fully recovered.

Diarrhea and bloody diarrhea can result from a number of diseases. Confirming shigella infection involves taking a sample of your stool to be tested in a lab for the presence of shigella bacteria or their toxins.

Shigella infection usually runs its course in five to seven days. Replacing lost fluids from diarrhea may be all the treatment you need, particularly if your general health is good and your shigella infection is mild.

Over-the-counter drugs

Talk to your doctor before taking an over-the-counter (OTC) drug intended to treat diarrhea. Diarrhea can be caused by a number of conditions, and OTC drugs may make some conditions worse.

If a lab test has confirmed that you have shigella infection, an OTC drug containing bismuth subsalicylate (Pepto-Bismol, Kaopectate) may help decrease the frequency of your stools and shorten the length of your illness. However, it isn't recommended for children, pregnant women or people who are allergic to aspirin.

Avoid taking OTC anti-motility drugs, such as loperamide (Imodium) and drugs containing the combination of diphenoxylate and atropine (Lomotil). These aren't recommended for shigella infection because they can decrease your body's ability to clear the bacteria and make your condition worse.

Antibiotics

For severe shigella infection, antibiotics may shorten the length of the illness. However, some shigella bacteria have become drug resistant. So your doctor may not recommend antibiotics unless your shigella infection is severe.

Antibiotics may also be necessary for infants, older adults and people who have HIV infection, as well as in situations where there's a high risk of spreading the disease.

Fluid and salt replacement

For generally healthy adults, drinking water may be enough to counteract the dehydrating effects of diarrhea.

Children may benefit from an oral rehydration solution, such as Pedialyte, available in drugstores. Many pharmacies carry their own brands.

Children and adults who are severely dehydrated need treatment in a hospital emergency room, where they can receive salts and fluids through a vein (intravenously), rather than by mouth. Intravenous hydration provides the body with water and essential nutrients much more quickly than oral solutions do.

Most people who have shigella infection get better on their own and don't need to see a doctor. If you or your child has severe symptoms or a high fever, you may need treatment.

What you can do

Before talking with your doctor, you may want to write a list of answers to the following questions:

• What are the symptoms?
• When did the symptoms start?
• Have you or your child been exposed to a person who has or had shigella infection?
• Do you or your child have a fever? If so, how high is it?

What to expect from your doctor

During the physical exam, your doctor may press on various parts of your abdomen to check for pain or tenderness. He or she may also use a cotton swab to get a stool culture or send you home with instructions for collecting and transporting a sample of your stool so that it can be tested for evidence of infection.