December 16th, 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. 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 Salmonella?
- What is happening with current Salmonella outbreaks?
- What is the current risk for Canadians from Salmonella?
- What measures should be taken for a suspected Salmonella infection case or contact?
What are the important characteristics of Salmonella?
Cause
Salmonella is a common gastroenteric infection that affects millions of individuals worldwide. Each year in Canada, over 88,000 people are infected with Salmonella. It is one of the top four causes of diarrheal illnesses globally, with cases ranging from mild to severe. More severe infections of Salmonella are rare, but can have life-threatening consequences.
The illness is caused by the Salmonella bacteria, which is characterized as a negative rod bacterium from the Enterobacteriaceae family. The genus Salmonella is divided into two different species, Salmonella bongori and Salmonella enterica. Between the two, thereare over 2,500 identified serotypes of Salmonella. While most strains are only transmitted between animals, there are 100 known serotypes that serve as the predominant sources of human cases.
S. bongori only infects cold-blooded species, whereas S. enterica can infect a variety of warm-blooded animals, including humans. S. enterica is divided into 6 subspecies: enterica (I), salamae (II), arizona (IIIa), diarizonae (IIb), houtinae (IV), and indica (VI). The most prevalent serotypes of S. enterica include Typhi, Paratyphi, Enteriditis, Typhemurium, and Choleraesuis.
Salmonella is most commonly contracted through the consumption of contaminated foods and by cross-contamination from improper hygiene practices.
WHO – Salmonella (non-typhoidal)
CDC – About Salmonella Infection
Genome Canada – A SystOMICS Approach To Ensuring Food Safety And Reducing The Economic Burden of Salmonellosis
Science Direct – Salmonella bongori
Signs, Symptoms, and Severity
S. enterica is known to cause four different clinical manifestations – gastroenteritis, bacteremia, enteric fever, and an asymptomatic carrier state.
- Gastroenteritis is described as typical “food poisoning”. It is usually characterized by mild to severe symptoms that last from 4-7 days. The Typhimurium serotype is the most common cause of gastroenteritis and is estimated to globally cause 1.3 billion cases and 3 million deaths annually.
- Bacteremia occurs in 3 to 10 percent of infected individuals. It is more severe and is more likely to occur in those who are immunocompromised or who have comorbid health conditions.
- Bacteremia presents as a mild fever, but as it progresses can cause chills, tachycardia, low blood pressure, abdominal pain, nausea, vomiting, diarrhea, hyperventilation, and in serious cases sepsis.
- Enteric fever (or Typhoid fever) is caused by the serotypes Typhi and Paratyphi. It manifests as a fever, headache, brachycardia, chest rash, anorexia, abdominal pain, and a host of other less common symptoms.
- The asymptomatic carrier state occurs when individuals test positive for Salmonella but present without any symptoms.
The majority of Salmonella cases manifest as typical gastroenteritis. Symptoms range from mild to severe; some cases are asymptomatic and some symptomatic cases persist as asymptomatic carrier cases after initial symptoms resolve. Onset of symptoms typically occurs within 6-72 hours after exposure and can last for 4-7 days.
The most common symptoms include:
- Diarrhea
- Fever
- Stomach cramps
- Headaches
- Nausea
- Vomiting
- Loss of appetite
More severe cases that do not resolve themselves may require additional antibiotic treatment, hospitalization, and can potentially lead to long-lasting health conditions. In rare circumstances, infections can spread through the bloodstream (bacteremia) to other organs.
Anyone can contract Salmonella, but certain groups are more at risk than others. Populations most at risk include:
- Children under the age of 5
- Pregnant women
- Adults 50+ with underlying medical conditions
- Adults 65+
- Individuals with weakened immune systems
- International travellers
- Sexually active individuals with an emphasis on men who have sex with men.
Canada.ca – Pathogen Safety Data Sheets: Infectious Substances – Salmonella enterica spp.
Cleveland Clinic – Bacteremia
CDC – About Salmonella Infection
PHAC – Symptoms of salmonellosis (Salmonella)
Laboratory Diagnosis
Diagnosing Salmonella requires laboratory testing of either stool, tissue, or bloodsamples. This process may be necessary when determining treatment options as the symptoms of Salmonella can present similarly to other enteric infections. The testing involves isolating the bacteria within a culture to identify it.Positive diagnoses should then be further analyzed through culture-independent diagnostic testing (CIDT) to map the genetic profile and determine the isolate’s serotype, and to identify if the strain has antimicrobial resistance. Multiplex PCR testing is another method of testing for enteric infections that can prove effective and easy.
If a symptomatic patient reports anorectal sexual activities, anoscopic evaluation is advised during physical exams.
CDC –Diagnostic and Public Health Testing
Microbiology Spectrum, 2024 – “Risk factors and provider awareness of sexually transmitted enteric pathogens among men who have sex with men”
Treatment
Most cases of Salmonella resolve themselves within a few days without requiring treatment. Severe infections are sometimes treated with antibiotics; however most people recover without needing to take them, and antibiotic prescription is discouraged because of the risk of antimicrobial resistance. When determining whether treatment is necessary, it is important to consult local surveillance systems to see if resistant strains have been reported in the area.
Dehydration is a common side effect of Salmonella infection, and patients should be advised to drink plenty of fluids and water while experiencing symptoms. Rehydration products such as Paedialyte and oral rehydration salts can be given to children who have severe diarrhea or vomiting. Do not give children under 12 years medication containing bismuth subsalicylate (Pepto-Bismol). Talk to patients before advising them to take anti-diarrheal medication such as Imodium, as it can make the infection last longer. Anti-diarrheal medications should not be taken if a patient is experiencing bloody diarrhea, fever, or diarrhea lasting more than two days.
CDC – About Salmonella Infection
WHO – Salmonella (non-typhoidal)
Epidemiology
In Canada, over 88,000 people are infected with Salmonella each year, although rates are probably much higher than reported. It is thought that only one in every thirty infections is reported, since the majority of people who contract Salmonella don’t get tested for food poisoning.
Rates of Salmonella tend to increase in the summer as warmer weather and unrefrigerated food creates favourable conditions for the bacteria.
CDC – About Salmonella Infection
Genome Canada – A SystOMICS Approach To Ensuring Food Safety And Reducing The Economic Burden of Salmonellosis
Mode of transmission
Salmonella is transmitted through the fecal-oral route. Humans can contract Salmonella through contamination of food, fomites, and through contact with human or animal fecal matter.
Salmonella is typically contracted by eating or drinking contaminated food or beverages. Common sources include:
- Raw or undercooked poultry, pork, and ground beef
- Raw or undercooked eggs and egg products
- Unpasteurized dairy products
Contamination commonly occurs in the kitchen due to unwashed hands, cutting boards, and dirty knives. The CDC reports that cases can also be linked to nuts, fruit, seeded vegetables, and other produce. Vegetables and produce can become contaminated by the manure in the soil in which they are grown.
Salmonella can also contaminate water, whether for drinking, irrigation, or recreational use. Infections arise when people drink unclean water, especially drinking water from streams, ponds, and lakes while swimming or camping.
Salmonella can also be transmitted by infected wild and domestic animals. Birds, livestock, amphibians, reptiles, dogs, cats, as well as other small pets including gerbils, hamsters, hedgehogs, and other small rodents can be carriers, even while appearing otherwise healthy. The bacteria is spread through animal feces, toys, bowls, and habitats. Flies can also contaminate food with Salmonella which can put humans at greater risk of infection.
Direct fecal-oral transmission is another way to contract Salmonella. Infected individuals can spread Salmonella to others by cross-contamination through unwashed hands or sexual contact. Is it not uncommon for infections to be spread throughout hospitals due to inadequate sanitization of hands and scopes. Hand washing is crucial to prevent infection.
CDC – About Salmonella Infection
PHAC – Causes of salmonellosis (Salmonella)
Canada.ca – Pathogen Safety Data Sheets: Infectious Substances – Salmonella enterica spp.
Surveillance
Confirmed and probable cases of Salmonella should be reported to the appropriate Provincial or Territorial Health Authority. Only confirmed cases are reported to the federal level on a case-by-case basis.
Infections and outbreaks of Salmonella and other gastroenteric illnesses in Canada are monitored by:
- The National Enteric Surveillance Program (NESP)
- FoodNet Canada
- The Canadian Notifiable Disease Surveillance System
The Salmonella Syst-OMICS Program is a pan-Canadian and international syndicate initiated in 2014. They are currently working on various initiatives surrounding Salmonella with the hopes of reducing the incidence and severity of Salmonella outbreaks globally and in Canada.
Their current projects include:
- Sequencing the genome of Salmonella isolates to advance research in the bacteria’s evolution
- Identification of virulence factors
- Developing methods to control contamination in foods
- Studying antimicrobial resistance in the bacteria
- Developing new surveillance techniques for early detection and monitoring of outbreaks to predict and prevent outbreaks.
PHAC – Surveillance of salmonellosis (Salmonella)
Salmonella Syst-OMICS – Salmonella Syst-Omics Overview
Prevention and Control
Adopting good hand washing practices is the best way to prevent the transmission of Salmonella. Individuals should wash their hands thoroughly with soap and water for at least 20+ seconds after using the washroom, before preparing food, after preparing food, and before eating.
Contracting Salmonella and other bacterial infections can also be prevented with sterile cooking practices and by following the steps “clean, separate, cook, and chill” while preparing food:
- Wash hands often and frequently wipe down surfaces between handling of raw meat.
- Separate raw meat, seafood, and eggs from other ingredients and use different cutting boards and cooking utensils.
- Ensure that food is cooked all the way through to kill off any harmful bacteria and be sure to use a meat thermometer.
- After preparing and eating, food must be refrigerated ideally within two hours to reduce the risk of bacterial growth.
Everyone should avoid consuming unpasteurized drinks, including milk and juices.
Patients should be reminded to follow travel health recommendations from the WHO, and tpractice safe eating anddrinking habits to lower the risk of contracting Salmonella while away. It is also important to be mindful about not swallowing pool or lake water when swimming.
Individuals should also take precautions when in contact with animals and should wash hands immediately after touching farm or wild animals and any animal feces. Hand washing is also suggested after touching pet food, treats, toys, and when cleaning up after pets.
If experiencing symptoms of food poisoning, health professionals should tell patients to stay home from work and keep their children home from school to lower the risk of contamination and spread. Individuals should also refrain from partaking in any sexual activities with partners to reduce the risk of transmission. Good hygiene practices must continue for at least two weeks after diarrhea ends, as the Salmonella bacteria can still be expelled through feces even if symptoms no longer persist.
CDC – About Salmonella Infection
PHAC – Causes of salmonellosis (Salmonella)
WHO – Salmonella (non-typhoidal)
Vaccine
In Canada, the Typhoid vaccine provides immunity against Typhoid Fever caused by S. enterica typhimurium. There are two versions of this vaccine, Parenteral (Typh-I) which lasts for up to three years, and oral (Typh-O) which lasts for up to seven years. While not 100% effective, these vaccines provide up to 50% protection against the typhimurium strain.
The Typhoid vaccine is recommended for:
- Individuals aged two and older travelling to endemic areas for extended periods of time.
- Employees working in laboratory settings who may be exposed to the typhimurium strain.
There is no vaccine for non-typhoidal salmonellosis currently available. Health professionals are advised to consult with patients who meet the above criteria to discuss whether the Typhoid vaccine is right for them.
Canadian Immunization Guide – Typhoid vaccines: Canadian Immunization Guide
Canada.ca – Pathogen Safety Data Sheets: Infectious Substances – Salmonella enterica spp.
What is happening with current Salmonella outbreaks?
At least 25 people in Canada have been infected with Salmonella across seven provinces due to direct and indirect contact with domesticated geckos and their habitats. The outbreak comprises individual unrelated cases spanning from August 2020 to September 2024, and has resulted in one death and three hospitalizations.
The Public Health Agency of Canada confirmed an outbreak of over 70 confirmed cases of Salmonella I and Salmonella typhimurium linked to snakes and rodent feed. Reported cases spanned from 2022 to 2024, with one death and 10 hospitalizations from the infection. Those who contracted the infection were either in direct or indirect contact with snakes and feeder rodents, or lived in the same residence that they were being kept in.
An outbreak of Salmonella occurred in late 2023: therewere 153 infections and 7 hospitalizations across Canada as a result of contaminated cantaloupes. The majority of the cases were children under the age of 5 and individuals 65 and older.
A 2020 multi-provincial outbreak of Salmonella was reported to be one of the largest in decades, with over 515 cases and almost 100 hospitalizations linked to contaminated red onions imported from California. The outbreak occurred between June and August 2020 and affected Canadians across seven provinces although predominately in B.C. and Alberta. A report published by the FDA found that a nearby sheep farm was most likely the source of contamination of the onions.
Public Health Ontario reported 1,711 cases of Salmonella and 231 hospitalizations in Ontario in 2022.
Food Safety News, October 8th, 2024 – New report looks back on Salmonella outbreak tied to red onions in Canada
Global News, October 1st, 2024 – Salmonella outbreak linked to geckos kills 1, infects 25 in Canada
CBC News, March 19th, 2024 – Salmonella infections across Canada linked to snakes and their rodent feed
CTV News, December 22nd, 2023 – Canadian death toll in cantaloupe salmonella outbreak rises to seven
PHO – Salmonellosis
What is the current risk for Canadians from Salmonella?
Anyone can contract Salmonella, but certain groups are more at risk than others. Populations most at risk include:
- Children under the age of 5
- Pregnant women
- Adults 50+ with underlying medical conditions
- Adults 65+
- Individuals with weakened immune systems
- International travellers
- Sexually active individuals
Research suggests that many clinicians are unaware that diarrheal pathogens such as Salmonella can be transmitted sexually. Men who engage in sexual activities with other men are at greater risk of contracting infections, as they can be asymptomatic carriers of the bacteria. Case reports have described acute Typhoid fever occurring in men who were in sexual contact with other men who were carriers of the S. typhi strain and in whom no other risk factors of transmission were found. Heterosexual men and women can also be at risk of transmitting enteric infections through anal sex and oral-anal sexual activities.
CDC – About Salmonella Infection
PHAC – Risks of salmonellosis (Salmonella)
Microbiology Spectrum, 2024 – “Risk factors and provider awareness of sexually transmitted enteric pathogens among men who have sex with men”
PHAC – Canadian Guidelines on Sexually Transmitted Infections
What measure should be taken for a suspected Salmonella infection case or contact?
Patients who believe that they have Salmonella should be advised to reach out to their primary health care providers. Patients should avoid preparing food for other people if they believe they are sick with Salmonella or other contagious enteric infections causing diarrhea.
Individuals should reach out to their physician when:
- Diarrhea or vomiting lasts more than two days
- Bloody urine or feces
- Fever higher than 38°C
- Symptoms of dehydration (little to no urine, dark urine, extreme thirst, dry mouth and throat, dizziness or lightheadedness, crying without tears)
- Long-term complications (diarrhea for months, infection that spreads elsewhere, reactive arthritis)