Shigella Infection

Reviewed on 10/13/2021

Shigella Infection Facts

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Picture of Gram-negative rod-shaped Shigella bacteria in a stool sample, CDC slide #6659
  • Shigellosis is an infectious disease characterized by diarrhea, fever, and stomach cramps.
  • The different species that can cause shigellosis are Shigella sonnei, Shigella flexneri, Shigella boydii, and Shigella dysenteriae.
  • Shigellosis is caused by Shigella species that multiply within and destroy gastrointestinal epithelial cells.
  • Shigellosis is highly contagious from person to person.
  • The incubation period for shigellosis is about one to three days.
  • Shigellosis patients are contagious until the person no longer sheds Shigella bacteria in feces.
  • Young children, small social groups, individuals with weakened immune systems, and men who have sex with other men are at increased risk for shigellosis.
  • Symptoms and signs of shigellosis include diarrhea, fever, stomach pains, and tenesmus.
  • Medical caregivers diagnose shigellosis by the patient's history, physical exam, and microbiological tests.
  • Most individuals resolve infection without treatment, but severe infections may require antibiotics.
  • Although most individuals will not have complications, severe infections can lead to dysentery, dehydration, hemorrhagic colitis, seizures, and death.
  • The prognosis for most individuals with shigellosis is excellent except in severe cases.
  • Although there is no vaccine available to prevent shigellosis, good hand-washing techniques, avoiding contaminated water and foods, and avoiding sexual activity with a person who has recently recovered are ways to reduce the risk of infection.

What Is Shigella Infection?

Shigellosis is an infectious disease caused by a group of bacteria called Shigella. Diarrhea, fever, and stomach cramps characterize the disease. About 500,000 people in the U.S. develop infections with Shigella bacteria, resulting in shigellosis.

What Are the Different Species of Shigella?

There are four different species of Shigella:

  • Shigella sonnei,
  • Shigella flexneri,
  • Shigella boydii, and
  • Shigella dysenteriae.

Shigella sonnei is predominant in the United States, while S. dysenteriae and S. boydii are rare in United States. Shigella dysenteriae, type I, can be lethal. Shigella species are gram-negative, nonmotile rod-shaped bacteria closely related to E. coli.

What Causes Shigellosis?

The cause of shigellosis is an infection of the gastrointestinal tract by Shigella bacteria.

  • The bacterial cells invade gastrointestinal epithelial cells and multiply within them.
  • As the bacteria multiply, they destroy epithelial cells and then spread to other epithelial cells.
  • This progression of the disease may result in severe dysentery in some patients.

Is Shigellosis Contagious?

The bacteria that cause shigellosis easily infect humans so that the disease is considered a highly contagious disease.

What Is the Incubation Period for Shigellosis?

  • The incubation period for shigellosis usually is about one to threes days, but the incubation period depends on the serotype and can vary from 12 hours to seven days.
  • Usually, the person is contagious during the incubation period and for about 10-14 days.
  • However, a person with a severe infection can be contagious for over six weeks.
  • However, the contagious period ends when the infected person no longer sheds Shigella bacteria in his or her feces.

What Are Shigellosis Symptoms and Signs?

Symptoms and signs of shigellosis include

  • diarrhea (sometimes there may be blood in the diarrhea),
  • fever,
  • stomach pains and stomach cramps, and
  • tenesmus (continual or recurrent feeling the need to evacuate the bowels).

How Do Medical Professionals Diagnose Shigellosis?

Medical caregivers preliminarily diagnose shigellosis based on the typical symptoms and signs of

  • pain,
  • fever, and
  • watery and/or bloody diarrhea and
  • the likelihood they have been exposed to sources of contamination.

To confirm the diagnosis, medical professionals can send stool samples to a laboratory to culture and identify the Shigella bacteria and to rule out other causes such as Campylobacter, Salmonella, Yersinia, and others that may share similar disease characteristics.

What Are Risk Factors for Shigellosis?

Risk factors for shigellosis include

  • young children, especially those in daycare centers,
  • travelers to developing countries, and
  • men who have sex with other men.
  • People with weakened immune systems (for example, cancer patients and HIV-positive individuals) and individuals within small social groups are at higher risk because it can spread easily from one person to another.

Transmission of the disease is usually by fecal/oral route, but ingestion of the bacteria associated with contaminated food (food poisoning) is also a risk factor.

What Is the Treatment for Shigellosis?

In most individuals who develop shigellosis, the patient's symptoms resolve without antibiotic treatment in about five to seven days.

  • Treatment at home can consist of fluids and rest.
  • Some physicians suggest that bismuth subsalicylate (Pepto-Bismol) may be helpful.
  • However, medications (for example, Imodium) that slow down the gastrointestinal tract's normal actions are contraindicated.
  • Severe shigellosis may require prescribed antibiotics. Your health care provider can help choose the best antibiotic for you after they have ordered laboratory tests to determine if the bacteria are resistant to certain types of antibiotics.

What Are Complications of Shigellosis?

Most patients will not experience complications, but severe infections can lead to

What Is the Prognosis for Shigellosis?

Because the disease is self-limiting, the prognosis for most individuals with shigellosis is excellent.

  • However, severe cases may last three to six weeks and develop complications, so the prognosis ranges from good to fair for most of these individuals.
  • However, in a few untreated children, the outcome is poor as they can die from the complications.

Is It Possible to Prevent Shigellosis?

  • Currently, there is no vaccine available to prevent shigellosis or Shigella infection.
  • You can reduce the risk of infection by good hand-washing techniques, avoiding swallowing water from ponds, lakes, and other untreated sources, and avoiding sexual activity with a person who has recently recovered from the disease for a few weeks.
  • Travelers should take precautions to avoid eating raw food items, drink only bottled water, and avoid ice in drinks when in areas where a recent outbreak has occurred.
Watery diarrhea is a symptom of shigellosis.

Shigellosis Symptom


  • Diarrhea is the frequent passage of loose, watery, soft stools with or without abdominal bloating, pressure, and cramps commonly referred to as gas or flatulence.
  • Causes of diarrhea include viral and bacterial infections, as well as parasites, intestinal disorders or diseases, reactions to medications, and food intolerance.
  • The main symptom of diarrhea is watery, liquid stools.
Reviewed on 10/13/2021
United States. Centers for Disease Control and Prevention. "Shigella: Shigellosis." Jan. 17, 2018. <>.