April 20, 2005
Named after the Japanese scientist Shiga who discovered it in 1897, Shigella is a type of bacteria that infects the intestinal tract. Four different groups of Shigella can affect humans, with some causing a mild illness and others a more severe one.
About 18,000 cases of Shigella infection are diagnosed each year in the United States, but many more go unreported because they involve only mild symptoms and sometimes no symptoms at all. The infection is most common during the summer months. Shigella rarely infects infants younger than 6 months old, but it is common in children 2 to 4 years old, especially those in child care.
Signs and Symptoms
Shigella can cause a spectrum of illnesses. Some people with a mild case have only loose watery stools, and a few may not have any symptoms at all. Others go on to develop a more severe disease known as dysentery, with abdominal cramps, high fever, loss of appetite, nausea, vomiting, and diarrhea, which may contain mucus and blood. Some children with severe cases of Shigella infection may need to be hospitalized. The most common complication is dehydration (an abnormally low level of fluid in the body). Rarely, Shigella bacteria can affect other organs in the body aside from the digestive tract. This can lead to arthritis, skin rashes, kidney failure, or neurological problems such as seizures, stiff neck, headache, lethargy, confusion, and hallucinations.

Shigella infections are very contagious. People who are infected pass Shigella bacteria in their stool. Other people may become infected if they come in contact with anything contaminated by stool from an infected person. This includes toys, surfaces in restrooms, and even food prepared by someone who has the infection. For instance, if children touch a contaminated surface such as a toilet or toy and then put their fingers in their mouths, they can become infected. Shigella can even be carried and spread by flies that have touched contaminated stool.
Because it doesn’t take many Shigella bacteria to cause an infection, the illness spreads easily in families and child-care centers. The bacteria may also spread in water supplies where sanitation is poor. Shigella can be passed in the person’s stool for about 4 weeks even after the obvious symptoms of illness have resolved (although antibiotic treatment can reduce the excretion of Shigella bacteria in the stool).
The best way to prevent the spread of Shigella is by frequent and careful hand washing with soap. This is important for all age groups. Children should be reminded to wash their hands, especially after they use the toilet and before they eat. This is especially important in a child-care setting.
If you’re caring for a family member who has diarrhea, wash your hands before touching other people and before handling food. (People with a diarrheal illness should not prepare food for others.) After someone with a Shigella infection uses a toilet, clean and disinfect the toilet before it’s used by anyone else.
Diapers of a child infected with Shigella should be properly disposed of in a sealed garbage can, and the diaper area should be wiped with disinfectant after use. Young children (especially those still in diapers) with a Shigella infection, or with diarrhea of any cause, should not be in contact with uninfected children.
Proper handling, storage, and preparation of food is also important – cold foods should be kept cold and hot foods should be kept hot to prevent bacterial growth.
Symptoms may occur from 1 to 7 days after exposure, but usually occur within 2 or 3 days.
Although it sometimes goes away on its own after a few days, untreated diarrhea may last a week or 2. However, antibiotics can shorten the illness.
Professional Treatment
To confirm the diagnosis of a Shigella infection, your child’s doctor may send a sample of your child’s stool to the laboratory to be tested for Shigella bacteria. Blood tests and other tests may also be needed to rule out other possible causes of the symptoms, especially if your child has a large amount of blood in the stool.
Once the diagnosis is made, some cases require no special treatment, but often antibiotics will be given to shorten the duration of the illness and to prevent the spread of Shigella bacteria to other people.
Hospitalization might be needed for children who become moderately or severely dehydrated or for those with problems in organs other than the digestive tract. While in the hospital they can be monitored and can receive necessary treatment such as intravenous fluid therapy or antibiotics.