L5: Foodborne Outbreak Pathogens

Gastroenteritis diseases in Australia burden

– 4.67 million cases of foodborne gastroenteritis due to all causes

– 47,900 hospitalisations & 38 deaths

– Costs of foodborne illness and its sequelae at AUD 2.44 billion/year

What percentage of people with gastroenteritis are diagnosed by laboratories

~5-10%

Epidemiology definition

The study of the complex relationships among hosts and infectious diseases to identify risk factors that can inform prevention strategies.

Risk factors for enteric diseases and outbreaks (4)

– Eating contaminated food.

– Handling raw meat

– Contact with farm animals

– Staying/visiting crowded venues (e.g. childcare)

Transmission of pathogen and disease severity is influenced by (5)

– Type of agent (e.g. bacteria, viruses, protozoa)

– Environment (e.g. live near wetland, refrigerators) and survival of agent in that environment

– R₀ : measure of how contagious the disease is

– Host (immune status, age, pregnancy)

– Transmission route (foodborne, waterborne, vector-borne, person-to-person)

Surveillance definition

the ongoing, systematic collection, recording, analysis, interpretation and dissemination of data for public health action.

How many enteric diseases/syndromes are notifiable in WA

16

Suspect most Gastroenteritis outbreaks in WA are which pathogen?

Is this pathogen notifiable?

Norovirus (not a notifiable disease)

Main transmission routes (2) of Gastroenteritis outbreaks in WA

Person-to-person transmission in residential care (41%) and childcare facilities (53%)

Most Foodborne gasto outbreaks in WA are which pathogen

Most (69%) are due non-typhoidal Salmonella

Which groups most susceptible to enteric diseases

Children, parents and immunocompromised people are most susceptible to illness

The most notified cause of gastroenteritis in WA

Campylobacter

Causes campylobacteriosis

4,506 notifications in 2025

4 most common notifiable enteric diseases in WA

1. Campylobacteriosis

2. Salmonellosis

3. Rotavirus

4. Cryptosporidiosis

The 2 main species of Campylobacter that cause human infection

~90% caused by Campylobacter jejuni

~ 10% Campylobacter coli and others

(~20 spp. most don’t cause human disease)

Campylobacter characteristics (gram, shape, atmosphere)

Gram negative, spiral rods, microaerophilic

Campylobacteriosis incubation period and symptoms

Incubation: 1 to 10 days (usually 2 to 5 days)

Moderate-severe illness:

- diarrhoea (sometimes blood in stool; average duration of 5 days)

- fever

- vomiting

- stomach cramps

- hospitalisation (<10%)

Campylobacteriosis transmission

faecal-oral, food-borne, animal-to-person

low risk of person-to-person transmission

Campylobacteriosis complications

Guillain-Barré syndrome, reactive arthritis, and post-infectious irritable bowel syndrome

Campylobacter ecology

• Colonises intestinal tract of many animals including chickens, other birds, pigs, cows, young dogs and cats

• Animal hosts are mostly asymptomatic.

• Meat from food production animals can be contaminated during slaughtering process

• Contaminated poultry accounts for 60-80% infections (~70-80% of poultry test positive)

• Beef/pork/lamb meat <5% – 20% of samples positive

Campylobacter does not survive well on (3) it is sensitive to __

Does not survive well on:

- chilled beef/ lamb/ pork carcasses

- surface of eggs

- does not grow in food

• Sensitive to drying and freezing

Does Campylobacter grow in food

No, just survives on some foods

Foodborne Campylobacteriosis outbreaks in Aus commonly are

2013 to 2019, 39 (4%) outbreaks associated with pate, chicken products in Australia

– 12 of those were linked chicken liver pate

– Campylobacter can penetrate poultry livers

Public health actions to reduce the number of campylobacteriosis notifications in WA

• Decrease colonisation via on-farm biosecurity measures

• Decrease contamination at slaughtering

• Decrease ingestion by freezing chicken meat prior to consumption

• Public education about handling and cooking chicken meat

• Avoid washing chicken meat

• Different chopping boards and knives for meat and vegetables

• Cooking and maintaining core temperature of ≥65°C

• Projects at OzFoodNet WA

• Risk factors for acquiring campylobacteriosis in the community

• Targeted surveys: Exposure to and consumption of chicken meat prior to illness and where the meat was purchased from to identify key ‘problem’ producers

Salmonella (non-typhoidal): gram stain, shape, atmosphere, spore forming or non spore forming?

• Gram negative rods, non-spore forming facultative anaerobe

Salmonella (non-typhoidal): two main species

Most infections caused by

• Two species: S. enterica (6 sub-species) and S. bongori

• 99% of human Salmonella spp. infections are caused by S. enterica subsp. enterica

Salmonella (non-typhoidal) growth conditions

• Non-fastidious; grow between 5 – 47°C (foodborne potential!)

Second most notified cause of gastroenteritis in WA

Salmonella (non-typhoidal)

99% of human Salmonella spp. infections are caused by S. enterica subsp. enterica

1,454 notifications in 2025

Salmonella (non-typhoidal) serotyping is based on

How many serovars/serotypes

Serotyping based on O, H, K antigens: >2600 serovars/serotypes

Salmonellosis incubation and disease characteristics

• Incubation: 8–72 hours

• Illness duration: 2–7 days

• Wide spectrum of disease from asymptomatic colonisation to acute gastroenteritis:

• diarrhoea (sometimes blood in stool; average duration of 5 days)

• fever

• vomiting

• stomach cramps

• hospitalisation (<10%)

Salmonellosis transmission

Faecal-oral, food-borne, water-borne, animal-person

Infectious period: most infectious while symptomatic and low risk post-recovery

Salmonellosis complications

Septicaemia, arthritis, appendicitis, meningitis or pneumonia

Salmonella ecology

• Salmonella bacteria isolated from a wide range of animal hosts and their food products: chicken, cow, sheep, pigs, fish, seafood and cold-blooded animals such as, lizards, snakes and frogs

• Can cause disease in animals, whilst some remain asymptomatic

• Contamination occur during slaughtering process, egg laying

• In an AUS survey, 43.3% of chicken meat at retail (n=859) was positive for Salmonella spp. The most prevalent serovar was S. Sofia at 30.5%

• In WA, Salmonella spp. were recovered from dust, feed, water, pooled faeces of chicken egg farms, 65% positive for S. Typhimurium

Salmonella Microbiological testing

1) Detection of the pathogen in stool specimens or suspect contaminated food samples.

2) Molecular typing (e.g. MLVA, WGS) allow us to identify specific strains of microorganisms by looking at their genetic material.

3) Finding a match between human and human and food samples can accurately identify food responsible for the outbreak

2 Important Salmonella enterica subs. enteric serovars/serotypes (word used interchangeably)

S. Typhimurium (STM): Salmonella enterica serovar Typhimurium

S. Enteritidis: Salmonella enterica serovar Enteritidis

Why are eggs associated with Salmonella outbreaks?

• Salmonella is commonly found in chickens and their surrounding

• Eggs can easily be contaminated with chicken faeces

• Eggs not always washed by egg producers

• Eggs can have cracks/pores that can lead to Salmonella contamination

• Poor temperature control can lead to rapid growth of Salmonella

• Raw egg contents often run over the eggshell

• Cooking/baking utensils not cleaned thoroughly between use

• Modern cooking includes many raw/potentially undercooked egg foods: poached eggs, scrambled eggs, chocolate mousse, meringue, tiramisu, homemade mayonnaise and aioli

Public health actions to reduce the number of Salmonella notifications in WA

On farm

• Biosecurity at the farm-vermin and fly control

• Flock vaccination

• Preventing transmission between breeder flocks and egg layers/chicken meat poultry

• Salmonella free meat-meal that is fed to chickens

Production

• Improving the slaughtering process to reduce contamination of chicken meat

• Egg grading

Education (Professional food handlers and general public)

• Safe handling and cooking of eggs and egg dishes

• Encourage testing

• Exclusion of cases, limit person-to-person transmission

Main salmonella serovar to cause outbreak in WA

S. Typhimurium (STM)

S. Enteritidis outbreaks

• In 2025, of WA cases, 91% of cases reported overseas travel, 7% WA acquired.

• Generally, no large outbreaks in Australia.

• Major cause of illness in overseas countries.

• Major outbreak associated with eggs and egg farm in NSW and VIC

Norovirus previously known as

Commonly referred to as

Previously known as: Norwalk virus

Commonly referred to as “winter stomach bug” or “winter vomiting disease”

Norovirus: virus characteristics

• Non-enveloped, positive-stranded RNA virus

• Highly diverse, genotype type vary temporally and geographically

• Human norovirus infections caused by genogroups GII, GI and GIV and >40 genotypes

• Cannot be cultured in vitro

Norovirus infection characteristics

• Incubation: 15–50 hours (average 30 hours)

• Illness duration: 1–2 days

• Mild to moderate illness:

• Diarrhoea (rarely blood in stool)

• Vomiting (more common in children)

• Lethargy

• Fever

• Abdominal pain

• Nausea

Norovirus transmission

• Transmission: primarily person-to-person

• Infectious period: most infectious while symptomatic (airborne, faecal/oral) and prolong shedding can occur

Norovirus: Complications and sequalae

Re-infection with a different strain, can cause severe disease in young and older people

Norovirus public health significance

• Foodborne transmission may occur via infected food handler preparing foods that will not undergo cooking (e.g. salads, garnishes) and contaminated shellfish

• Outbreaks most common in child care, health/aged care settings, schools, cruise ships and resorts.

• Self-limiting gastroenteritis, limited testing and under-reported

• Costs/case = AUD 390, Cost/all cases/year = AUD 128 million

Norovirus: Major control measures

– Encourage reporting to PHU (case management, infection control)

– Fact sheets with targeted audiences

– Hand hygiene

– Exclusion

– Media alerts

Norovirus outbreaks most commonly occur in

child care, health/aged care settings, schools, cruise ships and resorts.

Listeria monocytogenes characteristics

• Gram positive rod, facultative anaerobic intracellular bacteria

• Opportunistic pathogen that is widely distributed in the environment

• Historically recognised as a foodborne pathogen – Listeriosis

• 13 different serotypes based on flagellar and surface antigens

• Only three serotypes (1/2a, 1/2b, 4b) inflict disease in humans

• High infectious dose required for disease (host-factor dependent)

Listeriosis disease characteristics

Symptoms usually start within 2 weeks after eating food contaminated with Listeria. Can be up to 3 months

• Relatively rare, severe disease with high case fatality rate in high risk groups (immunocompromised, pregnant women).

• Can cause just diarrhoea/vomiting in low risk cases

Listeriosis disease characteristics

Pregnant women

Fever

Flu-like symptoms (muscle aches and fatigue)

Severity:

– Range from asymptomatic to mild

– Miscarriage, stillbirth, premature delivery, or life- threatening infection of the newborn.

Listeriosis disease characteristics

Non-pregnant people

Fever

Flu-like symptoms (muscle aches and fatigue)

Headache

Stiff neck

Confusion

Loss of balance

Seizures

 Symptoms in non-pregnant people can be severe

 Almost 1 in 20 non-pregnant people with invasive listeriosis die.

Listeriosis Public Health significance

• Costs/case = AUD 776,000, Cost/all cases/year = AUD 156.8 million

• National genomic surveillance to detect listeriosis outbreaks

• Education of high-risk groups (pregnant, elderly, immunocompromised) about foods they should avoid eating:

– Raw sprouts

– Unpasteurised milk/diary products

– Soft cheeses

– Cold deli meats

– Smoked/raw seafood

• National food recalls and pulled from shelves

• Food manufacturers having food safety plans

• National Food Safety policies on allowable limits of L. monocytogenes in food

Shiga toxin-producing E. coli (STEC)

• Gram negative rods that produce shiga toxin responsible for diarrhoea

• Lives in guts of domestic and pet animals → contaminated meat and vegetables (manure)

• Serotypes based on O and H antigens; O157:H7 leading cause of human infection

• PathWest perform whole genome sequencing on isolates to help detect outbreaks

Shiga toxin-producing E. coli (STEC)

Characteristics and management

– Transmission mode: Faecal-oral route via Animal-person or contaminated food/water

– Asymptomatic to severe diarrhoea with blood, abdominal pain, vomiting and fever

– Incubation: 1–10 days

– Duration: 5–7 days

– Complications: 5 to 10% develop haemolytic uraemic syndrome that leads to kidney failure and death

Vibrio parahaemolyticus

• Gram negative motile bacterium

• Naturally inhabits in marine and estuarine waters

• Transmission: Faecal-oral route, foodborne and waterborne

• Risk factors: wound exposure to seawater, consumption of raw/undercooked seafood

Vibrio parahaemolyticus

Recent outbreak in WA in 2024 - which food

Oysters

Clostridium perfringens

• Anaerobe

• Produces heat-stable toxin

• Food outbreaks, stews, gravies

• 2021 outbreak

Other gastroenteritis outbreak pathogens

Hepatitis A (outbreak from frozen berries in 2015)

Cryptosporidiosis

S. aureus

B. cereus

Ciguatera fish poisoning

Staphylococcus aureus

– Heat stable toxin

– Contamination from food handler with S. aureus sores or nasal colonisation

Bacillus cereus

– Toxin mediated vomiting/diarrhoea

– Rice dishes often implicated

Ciguatera fish poisoning

– Eating fish contaminated with toxins

– Ciguatoxic symptoms: diarrhoea, vomiting, numbness, itchiness and sensitivity to hot and cold

– 3 outbreaks in 2020 in QLD

The two the main notifiable pathogens that cause foodborne gastroenteritis in WA

1) Campylobacter

2) Salmonella (non typhoidal)

Outbreaks of STM are mostly attributed to

egg-based dishes