October 28, 2024
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 Natalie Maruna and Shyama Nanayakkara. Questions, comments, and suggestions regarding this disease brief are most welcome and can be sent to nccid@manitoba.ca.
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:
- What are the important characteristics of Shigellosis?
- What is happening with current Shigellosis outbreaks?
- What is the current risk for Canadians from Shigellosis?
- What measures should be taken for a suspected Shigellosis infection case or contact?
What are the important characteristics of Shigellosis?
Cause
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 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.
The disease is 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 prior to treatment, as some Shigella strains are resistant to antibiotics.
PHAC – for health professionals
CDC – diagnosis and treatment
Treatment
Preventing dehydration is part of the treatment for shigellosis. Those who have a Shigella infection should drink fluids frequently; patients with severe dehydration should be given intravenous fluids. Imodium (loperamide) or diphenoxylate with atropine (Lomotil) are contraindicated for those who have bloody diarrhea.
Recommended antibiotics for shigellosis are fluoroquinolones (such as ciprofloxacin), azithromycin, and third-generation cephalosporins (such as ceftriaxone). TMP-SMX and ampicillin can also be prescribed.
Multidrug-resistant (MDR) and extensively resistant (XDR) Shigella infections have been reported in high-resource countries, including Canada. MDR Shigella refers to strains resistant to at least three of the five main antibiotics that are typically used to treat Shigella. XDR Shigella strains are resistant to all five of the antibiotics used to treat Shigella infections. Cases of multidrug resistant strains of Shigella have been stable from 2018 to 2022; however, extensively resistant cases have risen from 1.0% to 6.6%. This increase in XDR cases is driven by the S. sonnei strain. Prior to the administration of any antibiotics, antimicrobial susceptibility testing is necessary due to the rise in drug-resistant Shigellosis.
PHAC – How shigellosis is treated
CDC – Information for Healthcare Professionals
PHO – Shigella Antimicrobial Resistance
Epidemiology
Shigellosis is endemic in most developing countries and is the most common cause of bloody diarrhea worldwide. The majority of deaths due to shigellosis occur among children younger than five years of age. Shigellosis is highly contagious and 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.
Those most susceptible to illness are:
- Young children – schools and childcare facilities are common locations for outbreaks.
- Travellers – particularly those who travel to areas with untreated tap water and/or inadequate sanitation
- Men who have sex with men
- People whose immune systems are weakened by disease or medical treatment
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
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
- Handwashing with soap and water, before and after eating, after using the bathroom and changing diapers, before preparing food, and after encountering an infected person.
- Washing raw fruits and vegetables thoroughly.
- Cooking food until the internal temperature reaches a safe level.
- Avoiding swallowing water in pools, lakes, or ponds.
- Throwing 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.
- Using a protective barrier such as a condom or gloves during sexual activity, and washing hands, genitals, anus, and any toys used.
- Follow safe food and water instructions when travelling.
PHAC – Prevention
CDC – Help prevent the spread of disease
Vaccine
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.
WHO – Immunization, Vaccines and Biologicals – Shigella
What is happening with current Shigellosis outbreaks?
In Canada, there are about 880 cases of shigellosis reported each year.
Alberta
A shigellosis outbreak was declared on June 5th, 2024 in Calgary, with 63 people testing positive for the S. sonnei strain. This outbreak resulted in 28 hospitalizations: 16 as a direct result of shigellosis, and 12 who tested positive after being admitted for different complications. An unrelated outbreak was reported in June of 2024 in the Maskwacis region of Alberta. The Maskwacis Health Services have not yet reported case numbers. Edmonton has been experiencing an ongoing shigellosis outbreak of the S. flexneri strain since August 17th, 2022: there have been 432 confirmed cases and 298 hospitalizations.
Quebec
On September 10th, 2022, Montreal confirmed an outbreak of 56 infections, primarily among men who have sex with men. 25 of the cases were multi-drug resistant (MDR) S. Sonnei infections.
British Columbia
In 2021, there was an outbreak of S. flexneri in the Downtown Eastside, Vancouver.
CBC News, July 24 2024 – Shigella outbreak hits Calgary shelters and encampments, sending 16 to hospital
AHS 2024 – Shigella Information
MHS – Ermineskin Cree Nation
AHS – Response to Shigella outbreak ongoing in Edmonton Zone
What is the current risk for Canadians from Shigellosis?
The risk to the general population is low. However, cases may be more prevalent in certain demographics, particularly children in childcare centres and schools and their families; travellers to locations with poor sanitation; men who have sex with men, and people experiencing homelessness. Many of the outbreaks occurring within the past five years in Canada have occurred among unsheltered populations in urban settings. In Ontario, males aged 30–39 are the demographic most at-risk for contracting shigellosis.
PHO – Infectious Disease Trends in Ontario
CDC – Shigella Infection Among Gay, Bisexual, and Other Men Who Have Sex with Men
PHAC – Shigellosis (Shigella)
What measures should be taken for a suspected Shigellosis infection case or contact?
Shigellosis is a nationally notifiable disease in all provinces and territories of Canada. Antimicrobial susceptibility testing should be conducted to ensure that the correct antibiotics are prescribed.
Cases of Shigellosis are recorded by the surveillance system that monitors cases of foodborne illness in Canada:
- FoodNet Canada
- PulseNet Canada
- the National Enteric Surveillance Program (NESP)
- the Canadian Notifiable Disease Surveillance System
PHAC – Surveillance