What is shigellosis?

Shigellosis is an infectious disease caused by a group of bacteria called Shigella, that causes bacterial dysentery. These bacterium cause disease by penetrating the lining of the large intestine, causing swelling and sores. This causes diarrhoea, fever, and stomach cramps 1-2 days after initial exposure.
The Shigella germ is actually a family of bacteria that can cause diarrhoea in humans. They are microscopic living creatures that pass from person to person. Shigella were discovered over 100 years ago by a Japanese scientist named Shiga, for whom they are named. There are several different kinds of Shigella bacteria: Shigella sonnei accounts for over two-thirds of the shigellosis in the United States. A second type, Shigella flexneri, accounts for almost all of the rest. Other types of Shigella (such as Shigella dysenteriae and Shigella boydii) are rare in developed countries, though they continue to be important causes of disease in the developing world.

Statistics on shigellosis

Every year in the United States, there are approximately 14 000 laboratory confirmed cases of shigellosis, and an estimated 448 240 total cases. Shigellosis occurs worldwide, and it tends to occur whenever war, natural calamities (e.g. earthquakes, floods), or unhygienic living conditions result in overcrowding and poor sanitation. Shigella boydii and Shigella dysenteriae occur more commonly in developing countries.

Risk factors for shigellosis

The Shigella bacteria pass from one infected person to the next. Shigella are present in the diarrheal stools of infected persons while they are sick and for a week or two afterwards. Most Shigella infections are the result of the bacterium passing from stools or soiled fingers of one person to the mouth of another person. This happens when basic hygiene and handwashing habits are inadequate. It is particularly likely to occur among toddlers who are not fully toilet-trained. Family members and playmates of such children are at high risk of becoming infected.
Shigella infections may be acquired from eating contaminated food. Contaminated food may look and smell normal. Food may become contaminated by infected food handlers who forget to wash their hands with soap after using the bathroom. Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected feces and then contaminate food. Shigella infections can also be acquired by drinking or swimming in contaminated water. Water may become contaminated if sewage runs into it, or if someone with shigellosis swims in it.
Therefore those at risk of the infection include children in child-care centres, persons in custodial institutions, long term care facilities, military camps, international travelers, and those who live in overcrowded populations with inadequate sanitation.

Progression of shigellosis

Children under five years are predominantly affected. The period between exposure to the bacterium and development of symptoms is short, usually of two days duration. The onset is acute, with fever, fatigue, abdominal pain and watery diarrhoea. As the disease increases in intensity, bloody diarrhoea with mucous, faecal urgency and severe cramping abdominal pain occur. Nausea and vomiting, headache and convulsions (in children) may occur.

How is shigellosis diagnosed?

Many different kinds of diseases can cause diarrhea and bloody diarrhoea, and the treatment depends on which germ is causing the diarrhoea. Determining that Shigella is the cause of the illness depends on laboratory tests that identify Shigella in the stools of an infected person. These tests are sometimes not performed unless the laboratory is instructed specifically to look for the organism. The laboratory can also do special tests to tell which type of Shigella the person has and which antibiotics, if any, would be best to treat it.

Prognosis of shigellosis

The disease is self-limiting, usually resolving within 5 to 7 days without antibiotics. In severe cases, the infection may last 3 to 6 weeks.
Persons with diarrhoea usually recover completely, although it may be several months before their bowel habits are entirely normal. About 3% of persons who are infected with one type of Shigella, Shigella flexneri, will later develop pains in their joints, irritation of the eyes, and painful urination. This is called reactive arthritis. It can last for months or years, and can lead to chronic arthritis which is difficult to treat. Reactive arthritis can be caused by a reaction to Shigella infection, but happens only in people who are genetically predisposed to it.
Once someone has had shigellosis, they are not likely to get infected with that specific type again for at least several years. However, they can still get infected with other types of Shigella.

How is shigellosis treated?

Treatment consists mainly or replacing fluids and salts lost due to the diarrhoea.
Normally, oral replacement is sufficient, however those with severe dehydration may need intravenous fluids. Antibiotics may be given if the person is very young, or very old, when the disease is severe, and when there is a high risk of spreading the disease to other persons. In those cases, antibiotics such as trimethoprim-sulfamethoxazole, norfloxacin, ampicillin, or cotrimoxazole may be given. Antidiarrhoeal drugs such as Immodium may prolong the infection and should not be used.


  1. Centre for Disease Control. Disease Information: Shigellosis. Available from: URL link
  2. Kumar, Parveen & Clark, Michael. 1999, Clinical Medicine, WB Saunders, London.
  3. The Merck Manual. Shigellosis in Chapter 190, Bacterial Infections. www.merck.com