November 22, 2022

NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. While not a formal literature review, information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and peer-reviewed literature.

This disease debrief was prepared by Shyama Nanayakkara. Questions, comments, and suggestions regarding this disease brief are most welcome and can be sent to

What are Disease Debriefs? To find out more about how information is collected, see our page dedicated to the Disease Debriefs.

Questions Addressed in this debrief:

  1. What are the important characteristics of Shigellosis?
  2. What is happening with current Shigellosis outbreaks?
  3. What is the current risk for Canadians from Shigellosis?
  4. What measures should be taken for a suspected Shigellosis infection case or contact?

What are the important characteristics of Shigellosis?


Shigellosis is an acute, invasive, enteric bacterial infection that affects the digestive system. It is caused by a group of bacteria called Shigella.

Shigella are Gram-negative, non-motile bacilli belonging to the family Enterobacteriaceae. The genus Shigella includes four species: S. dysenteries, S. flexneri, S. boydii, and S. sonnei (also designated as A, B, C and D groups, respectively). The first three species include multiple serotypes.

Both S. sonnei and S. boydii typically cause relatively minor illnesses.  S. flexneri is the chief cause of endemic shigellosis in developing countries. S. dysenteriae, also known as Shiga bacillus, produces a potent cytotoxin (Shiga toxin) that causes an illness that is more severe, more prolonged, and more frequently fatal than an illness caused by other Shigella.

Shigella is transmitted through the fecal-oral route. The bacteria pass through the gastrointestinal tract upon ingestion until they reach the small intestine. There they begin to multiply until they reach the large intestine (colon). Shigella causes acute bloody diarrhea by invading and causing patchy destruction of the colonic epithelium.

Humans and a few primates are the only reservoirs of Shigella. Shigella is easily transmitted and requires only a small number of bacteria to cause illness. It can be spread through direct contact with an infected person, consuming contaminated food, or consuming contaminated water. The organism can also be spread by flies.

PHAC – Shigellosis (Shigella)

PHAC – Cause of shigellosis

WHO – Immunization, Vaccines and Biologicals – Shigella

CDC – Shigella

Signs, Symptoms and Severity

Symptoms may appear within 1–2 days of encountering Shigella. In some circumstances, infection symptoms may start to show up as soon as 12 hours after contact. The duration of the symptoms can vary. Typically, symptoms last for 5 to 7 days. Some people who contract the infection show no signs of illness. However, their feces may continue to be infectious and contagious for up to 4 weeks after illness.

Signs and symptoms may include:

  • diarrhea (liquid stools that contain visible blood, with or without mucus)
  • abdominal cramps and tenesmus (unproductive, painful straining)
  • fever
  • nausea or vomiting
  • mild to moderate dehydration

The severity of illness and risk of death is the least with disease caused by S. sonnei and the greatest with infection by S. dysenteries, which produce a potent cytotoxin.

The disease is also most likely to be severe, and the risk of death greatest, among:

  • infants and elderly
  • children who are not breastfed
  • children recovering from measles
  • malnourished children and adults
  • any patient who develops dehydration, unconsciousness or hypo- or hyperthermia, or has a history of convulsions

Rare complications from shigellosis include:

  • Reiter’s syndrome: Reactive arthritis after infection, which can cause joint pain, eye irritation, and painful urination commonly with S. flexneri
  • septicemia (bloodstream infections) among patients with weakened immune systems, such as those with HIV, diabetes, cancer, or severe malnutrition
  • Hemolytic Uremic Syndrome (HUS), a condition that affects small blood vessels and that can cause anemia
  • convulsions, especially among young children
  • rectal prolapse
  • toxic megacolon, a rare complication that occurs when the colon becomes paralyzed, preventing a bowel movement or passing gas
  • intestinal perforation

PHAC – Symptoms of shigellosis,

PHAC – Clinical manifestations

CDC – Information for Healthcare Professionals

Laboratory Diagnosis

Bloody or mucoid stools are strong indicators of the disease, so shigellosis can be diagnosed clinically. However, differential diagnoses include enteritis caused by Campylobacter jejuni, Escherichia coli, Yersinia enterocolitica, Salmonella enteritidis and Entamoeba histolytica, which also cause bloody diarrhea and other symptoms similar to shigellosis. Amebiasis patients frequently have blood in their stools, but the blood is typically dark brown rather than bright red, as it is in Shigella infections.

When shigellosis is suspected, a stool sample must be tested using either a rapid diagnostic test that detects the genetic makeup of the bacteria or a culture that isolates the bacteria.

Antimicrobial susceptibility testing is required to treat shigellosis with an antibiotic because shigella is resistant to many common antibiotics. 

PHAC – For health professionals

CDC – diagnosis and treatment


To avoid dehydration, those who have a Shigella infection should consume lots of fluids. Imodium (loperamide) or diphenoxylate with atropine should not be used by people with bloody diarrhea (Lomotil). Symptoms could get worse if you take these drugs.

Preventing dehydration is part of the treatment for shigellosis. A patient with severe dehydration needs to be admitted to the hospital and given intravenous fluids. Recommended antibiotics for shigellosis are fluoroquinolones (such as ciprofloxacin), azithromycin, and third-generation cephalosporins (such as ceftriaxone).

Some Shigella strains are resistant to antibiotics. Multidrug-resistant Shigella infections have been reported in high-resource countries. The National Antimicrobial Resistance Monitoring System (NARMS) of the CDC has discovered an increase in the number of Shigella isolates with decreased azithromycin susceptibility and resistance to ciprofloxacin. Prior to the administration of any antibiotics, antimicrobial susceptibility testing is recommended due to the rise in drug-resistant Shigellosis.

PHAC – How shigellosis is treated

CDC – Information for Healthcare Professionals


Shigellosis is endemic in most developing countries and is the most important cause of bloody diarrhea worldwide. The majority of deaths occur among children younger than five years of age. Shigellosis outbreaks are most frequent in overpopulated, underdeveloped areas with poor sanitation, insufficient hygiene standards, and contaminated water sources. Internally displaced individuals and refugees are particularly vulnerable. Shigella germs are easily transmitted from person to person, so outbreaks can happen among any race, ethnicity, or social circle.

In the Canadian province of Alberta, there is a shigellosis outbreak with S. flexneri among Edmonton’s inner-city residents. A total of 115 patients with the 173-person Shigella infection needed hospitalization over the course of three months, beginning in mid-August 2022.

The most typical categories of people who are most susceptible to illness are;

  • Among young children – germs can spread easily among children, family members and others in the community. Schools and childcare facilities are common locations for outbreaks.
  • Travelers – visit to nations with untreated tap water, inadequate sanitation for food, drinking and recreational water, and Shigella-contaminated surfaces
  • Gay or bisexual men – men who have sex with men are more likely to get Shigella infection than other adults.
  • People whose immune systems are weakened (such as HIV) or are on medical treatment (such as chemotherapy for cancer)

Mode of transmission

  • Touching surfaces, such as toys, bathroom fixtures, changing tables, and diaper pails, contaminated with Shigella
  • Changing the diaper of a child with an infection
  • Taking care of a person with an infection, including cleaning up after the person uses the toilet
  • Eating food prepared by someone with a Shigella infection
  • Swallowing recreational water, such as lake water or improperly treated swimming pool water
  • Swallowing contaminated drinking water, such as water from a well that’s been contaminated with sewage or flood water
  • Exposure to stool  during sexual contact with someone with a Shigella infection

PHAC – How shigellosis is spread, Cause of shigellosis

WHO – Immunization, Vaccines and Biologicals – Shigella

CDC – Shigella

AHS – Response to Shigella outbreak ongoing in Edmonton Zone


Prompt detection and reporting of cases of bloody diarrhea is essential to monitoring and controlling the epidemic of shigellosis.

Shigellosis is a nationally notifiable disease in all provinces and territories of Canada.

In addition, there is a surveillance system to monitor cases of foodborne illness in Canada. These include:

  • FoodNet Canada
  • PulseNet Canada
  • the National Enteric Surveillance Program (NESP)
  • the Canadian Notifiable Disease Surveillance System

PHAC – Surveillance

CDC – National Shigella Surveillance Overview

Prevention and Control

Shigella-caused dysentery can be avoided in large part by taking precautions against the organism’s transmission to others and within the community. These comprise

  • Wash your hands with soap and water thoroughly and often, especially before and after eating, after using the bathroom and changing diapers, before preparing food, and after encountering an infected person.
  • Before eating, wash raw fruits and vegetables thoroughly.
  • Cook food until the internal temperature reaches a safe level.
  • Avoid swallowing water in pools, lakes, or ponds.
  • Throw away soiled diapers in a lined garbage can with a lid.
  • Avoiding sexual activity with someone who has diarrhea or has recently recovered from diarrhea
  • Follow safe food and water instructions when travelling to other countries.

PHAC – Prevention

CDC – Help prevent the spread of disease


Although several Shigella vaccines are being evaluated at different preclinical and clinical development stages, there are currently no widely available licensed vaccines against Shigella, including in Canada. In addition to the potential direct effects on morbidity and mortality, the rise of antimicrobial resistance to Shigella means that a Shigella vaccine might also have indirect effects on lowering the use of antibiotics and the subsequent emergence of antimicrobial resistance (AMR). A crucial goal for public health is the development of a Shigella vaccine because it may result in herd immunity and offer defence against all types of diarrheas

WHO – Immunization, Vaccines and Biologicals – Shigella

What is happening with current Shigellosis outbreaks?

Every year in Canada, there are about 880 cases of shigellosis cases that are reported.

According to Alberta Health Services (AHS), Edmonton is experiencing a shigellosis outbreak. Since the first case of shigellosis caused by S. flexneri was reported on August 17th, 2022, there have been 173 confirmed cases in Edmonton, and 115 people have needed hospitalization (by November 17, 2022). The Radius Community Health Clinic in Edmonton’s inner city screens every patient for signs of a Shigellosis infection. Authorities fear that as the weather gets colder, the outbreak will worsen as people huddle together for warmth in tents or other shelters.

In 2021, there was an outbreak of S. flexneri in Downtown Eastside, Vancouver.

CBC News, November 17 2022 –

 AHS – Response to Shigella outbreak ongoing in Edmonton Zone

What is the current risk for Canadians from Shigellosis?

Shigella infection outbreaks are common in childcare centres and schools. Being so contagious, these bacteria frequently cause infections in young children, who then spread them to their families and neighbors.

Travelers who visit locations with poor sanitation and hygiene standards are more likely to contract Shigella and bacterial strains that are resistant to the antibiotics used to treat them. Through contaminated food, water (drinking and recreational water), or surfaces, travellers may encounter bacteria. By strictly adhering to food and water safety precautions and frequently washing their hands with soap, travellers can protect themselves.

PHAC – Shigellosis (Shigella)

What measures should be taken for a suspected Shigellosis infection case or contact?

If you or a member of your family has bloody diarrhea, intense stomach pain, or tenderness, especially if you also have a fever or feel extremely ill, contact your healthcare provider immediately. If you have any other medical conditions or a compromised immune system, such as from HIV infection or chemotherapy treatment, let your healthcare provider know as you may be more susceptible to developing severe illness.

If a healthcare provider prescribes an antibiotic, take it exactly as directed and finish taking all the pills even if you feel better. Appropriate use of antibiotics can help prevent antibiotic resistance and the spread of resistant bacteria.

Do not prepare food or pour water on other people if you think you are sick with shigellosis.

Stay home while you are sick. Children with shigellosis should not attend childcare, school, or group activities while they have diarrhea.

Talk to your healthcare provider or visit a travel health clinic 6 weeks before you travel.

PHAC – Shigella What to do if you become ill

CDC – Information for Healthcare Professionals