Common Causes of Foodborne Illness and Food Poisoning

Bacteria are a major cause of food poisoning, but they are not the only food safety hazard. Foodborne illness can also result from viruses, parasites and harmful toxins.

Moulds can spoil food, and some types may produce dangerous substances called mycotoxins. Understanding these hazards helps food handlers recognise risks and apply the correct food safety controls.

What Causes Foodborne Illness?

Foodborne illness may be caused by:

• Harmful bacteria
• Viruses
• Parasites and protozoa
• Toxins produced by bacteria
• Mycotoxins produced by certain moulds
• Other biological or chemical contaminants

Food contaminated with harmful microorganisms may look, smell and taste completely normal.

Campylobacter Food Poisoning

Campylobacter is one of the most common causes of foodborne illness in the UK. It is strongly associated with raw or undercooked poultry, particularly chicken.

Sources of Campylobacter

Possible sources include:

• Raw or undercooked poultry
• Other raw or undercooked meat
• Unpasteurised milk
• Untreated water
• Contact with infected animals
• Cross-contamination from raw food

Bacteria from raw chicken can spread easily to:

• Hands
• Chopping boards
• Knives and utensils
• Work surfaces
• Refrigerator handles
• Cooked and ready-to-eat food

Campylobacter Symptoms and Incubation Period

Symptoms usually begin between two and five days after infection, although the incubation period can be longer.

Symptoms may include:

• Diarrhoea, which may sometimes contain blood
• Stomach pain and cramps
• Fever
• Headache
• Nausea
• Vomiting in some cases

Most people recover within approximately one week. However, the bacteria may continue to be passed in faeces for two or three weeks after the illness.

Rare complications can include reactive arthritis and Guillain-Barré syndrome.

How to Prevent Campylobacter

• Cook poultry thoroughly
• Keep raw poultry separate from ready-to-eat food
• Wash hands after handling raw meat
• Clean and disinfect contaminated surfaces
• Use separate equipment where required
• Do not wash raw chicken
• Use pasteurised milk

Washing raw chicken can spread contaminated droplets to hands, clothing, equipment and surrounding surfaces.

Salmonella Food Poisoning

Salmonella bacteria can live in the digestive systems of humans and animals. Food may become contaminated during production, processing or preparation.

Sources of Salmonella

Salmonella may be associated with:

• Raw or undercooked poultry
• Raw or undercooked meat
• Raw or lightly cooked eggs that are not covered by recognised UK safety schemes
• Unpasteurised milk and dairy products
• Contaminated fruit and vegetables
• Contaminated hands, equipment and surfaces
• Contact with infected animals

Salmonella Symptoms and Incubation Period

Symptoms commonly begin between six and 72 hours after infection.

They may include:

• Diarrhoea
• Abdominal pain
• Nausea
• Vomiting
• Fever
• Headache

Most people recover within several days. However, the illness can be more serious for:

• Babies and young children
• Older people
• People who are pregnant
• People with weakened immune systems
• People with certain underlying health conditions

How to Prevent Salmonella

• Cook meat and poultry thoroughly
• Use eggs appropriate for the intended cooking method
• Avoid unpasteurised dairy products where they present a risk
• Prevent cross-contamination
• Wash hands thoroughly
• Store food at safe temperatures
• Clean and disinfect food-contact surfaces

Clostridium perfringens Food Poisoning

Clostridium perfringens is a spore-forming bacterium commonly associated with food prepared in large quantities.

Foods linked to this type of food poisoning may include:

• Stews
• Casseroles
• Curries
• Gravy
• Roasted meat
• Meat dishes
• Foods prepared in large batches

How Clostridium perfringens Survives Cooking

The bacterium can produce spores capable of surviving normal cooking. If cooked food is cooled too slowly or held at an unsafe temperature, the spores may develop into active bacteria and multiply rapidly.

Problems commonly arise when:

• Large quantities of food are cooled too slowly
• Food is left at room temperature
• Hot food is held below 63°C for too long
• Cooked food is reheated inadequately
• Food is prepared too far in advance

Clostridium perfringens Symptoms

Symptoms normally begin approximately eight to 24 hours after eating contaminated food.

Common symptoms include:

• Abdominal pain
• Stomach cramps
• Diarrhoea

Vomiting and fever are less common. The illness is usually short-lived, but vulnerable people may be affected more seriously.

How to Prevent Clostridium perfringens

• Cook food thoroughly
• Keep hot food at 63°C or above
• Cool cooked food as quickly as possible
• Divide large batches into smaller portions
• Use shallow containers or suitable rapid-cooling equipment
• Refrigerate food without unnecessary delay
• Reheat food until steaming hot throughout

E. coli O157 Food Poisoning

E. coli O157 is a particularly dangerous type of Shiga toxin-producing E. coli, commonly abbreviated to STEC.

Only a very small number of bacteria may be needed to cause serious illness.

Sources of E. coli O157

Possible sources include:

• Undercooked minced beef and burgers
• Contaminated cooked meat
• Unpasteurised milk
• Contaminated fruit and vegetables
• Untreated water
• Contact with farm animals or their environment
• Contaminated hands, surfaces and equipment
• Person-to-person transmission

E. coli O157 Symptoms

Symptoms commonly develop within a few days but may begin sooner or later.

They can include:

• Severe stomach cramps
• Diarrhoea
• Bloody diarrhoea
• Nausea
• Vomiting
• Fever in some cases

A serious complication called haemolytic uraemic syndrome, or HUS, may develop. HUS can damage the kidneys and is particularly dangerous for children, older people and other vulnerable individuals.

How to Prevent E. coli O157

• Cook minced meat and burgers thoroughly unless a validated safe process is used
• Separate raw and ready-to-eat food
• Use separate equipment where required
• Wash hands thoroughly
• Clean and disinfect surfaces effectively
• Use pasteurised milk
• Wash fresh produce where appropriate
• Follow the Food Standards Agency’s cross-contamination guidance

Listeria Food Poisoning

Listeria monocytogenes is unusual because it can continue to grow slowly at refrigeration temperatures.

The illness it causes, known as listeriosis, is uncommon but can be extremely serious for vulnerable people.

Foods Associated with Listeria

Listeria is particularly associated with chilled ready-to-eat foods, including:

• Cold-smoked and cured fish
• Pâté
• Soft mould-ripened cheeses
• Soft blue cheeses
• Cooked sliced meats
• Pre-packed sandwiches
• Prepared salads
• Some chilled ready meals
• Unpasteurised dairy products

Who Is Most at Risk from Listeria?

People at increased risk include:

• People who are pregnant
• Unborn and newborn babies
• Older people
• People with weakened immune systems
• People receiving immunosuppressive treatment
• People with certain long-term health conditions

Severe listeriosis may cause sepsis, meningitis, miscarriage, stillbirth or serious illness in a newborn baby.

How to Prevent Listeria

• Keep chilled ready-to-eat food at 5°C or below as good practice
• Follow use-by dates
• Follow storage instructions after opening
• Maintain the cold chain
• Prevent cross-contamination
• Clean and disinfect equipment thoroughly
• Pay particular attention to food served to vulnerable people

Norovirus and Food Handling

Norovirus, sometimes called the winter vomiting bug, is a highly infectious virus that can occur at any time of year.

Unlike bacteria, norovirus does not multiply in food. However, food can carry the virus and pass it to somebody who eats it.

How Norovirus Spreads

Norovirus can spread through:

• Contaminated hands
• Food handled by an infected person
• Contaminated water
• Contaminated surfaces and equipment
• Direct contact with an infected person
• Droplets released during vomiting

Norovirus Symptoms

Symptoms normally begin between 12 and 48 hours after infection and may include:

• Sudden vomiting
• Watery diarrhoea
• Stomach cramps
• Nausea
• Headache
• A high temperature
• Aching limbs

Most people begin to feel better within two or three days, although they can continue spreading the virus after symptoms stop.

How to Prevent Norovirus

• Wash hands thoroughly with soap and water
• Exclude affected food handlers from work with or around open food
• Apply the 48-hour symptom-free rule
• Clean and disinfect contaminated areas correctly
• Dispose of contaminated food safely
• Wash contaminated clothing and linen appropriately

Alcohol hand gel should not be relied upon as a substitute for washing hands properly with soap and water.

Hepatitis A and Food Contamination

Hepatitis A is a viral infection that affects the liver. It can spread through food or water contaminated with infected faecal matter.

Possible sources include:

• Food handled by an infected person
• Contaminated water
• Raw or undercooked shellfish from contaminated water
• Contaminated fruit and vegetables
• Poor hand hygiene

Symptoms of Hepatitis A

Symptoms may include:

• A high temperature
• Fatigue
• Headache and muscle pain
• Nausea or vomiting
• Abdominal pain
• Diarrhoea or constipation
• Dark urine
• Pale faeces
• Yellowing of the skin or eyes, known as jaundice

How to Prevent Hepatitis A

• Maintain effective hand hygiene
• Use safe drinking water
• Purchase shellfish from approved suppliers
• Wash produce where appropriate
• Exclude infected food handlers in accordance with medical and public-health advice
• Follow travel-health vaccination advice where relevant

Moulds and Mycotoxins in Food

Moulds are fungi that can grow on food. Some are intentionally used in food production, including the production of certain cheeses.

Other moulds can spoil food or produce harmful substances called mycotoxins.

Mould growth may be encouraged by:

• Warm or humid conditions
• Damp storage areas
• Damaged packaging
• Food being stored for too long
• Incorrect temperature control
• Poor stock rotation

Can Mouldy Food Be Made Safe?

Removing the visible mould does not always make food safe. Mould can spread below the surface, and toxins may remain even when the affected section has been removed.

Food handlers should follow workplace procedures and manufacturer guidance. Mouldy food should not be served unless the mould is an intended and controlled part of the product.

Bacterial Toxins in Food

Some bacteria can produce toxins in food. Certain toxins may survive cooking or reheating, which means that heating contaminated food may not make it safe.

Toxin production can be encouraged when food is:

• Stored at an unsafe temperature
• Cooled too slowly
• Left at room temperature for too long
• Handled after cooking
• Stored beyond its safe shelf life

This is why safe food handling must begin before cooking and continue throughout storage, preparation and service.

Why Food May Appear Safe When It Is Not

Harmful microorganisms are microscopic and cannot normally be seen with the naked eye.

Food may look, smell and taste normal while still containing enough harmful bacteria, viruses or toxins to cause illness.

Food should never be tasted to determine whether it is safe. Instead, food handlers must rely on:

• Use-by dates
• Storage instructions
• Temperature records
• Food safety procedures
• Supplier information
• Effective stock rotation

Preventing Foodborne Illness

The main food safety controls include:

• Cooking food thoroughly
• Maintaining safe chilled and hot-holding temperatures
• Cooling food rapidly
• Preventing cross-contamination
• Cleaning and disinfecting effectively
• Washing hands correctly
• Excluding ill food handlers
• Following use-by dates
• Using approved suppliers
• Maintaining effective pest control

Protecting Customers from Foodborne Disease

Understanding the common causes of foodborne illness helps food handlers recognise hazards, apply effective controls and protect the people they serve.

Good hygiene, safe storage, temperature control and the prevention of cross-contamination remain essential because dangerous microorganisms may be present even when food appears completely normal.