Most food-related illness has a simple cause: germs get onto food and multiply there. You often cannot see, smell or taste them. Food can be dangerous and look completely normal.
What hazards are there?
- Biological hazards: bacteria, viruses, parasites and moulds. They are the most common cause of foodborne illness.
- Chemical hazards: for example cleaning and disinfecting products, pesticides or residues.
- Physical hazards (foreign bodies): for example splinters of glass, pieces of metal, bones, splinters of wood, jewellery or plasters.
- Allergens: substances that cause severe reactions in sensitive people. They have a lesson of their own, lesson 8.
How do bacteria multiply?
Bacteria need four things: warmth, moisture, nutrients and time. They multiply especially well in moist foods rich in protein, such as meat, poultry, fish, eggs, dairy products, rice and pasta.
- In a fridge, most bacteria multiply only slowly.
- Between chilled and hot-holding temperatures, roughly between 7 °C and 60 °C, they multiply quickly.
- Heat kills most bacteria. Cold does not kill them. It only slows them down.
- Some bacteria form spores. These are tough resting forms that can survive cooking.
- Some bacteria form toxins (poisons). Some of these are heat-stable: the poison remains even after the bacteria have been killed by heating.
- Viruses do not multiply in food, only in cells. But food can carry them, and a few viruses are enough to cause illness.
Important germs at a glance
- Salmonella: mainly in raw poultry, meat, raw eggs and dishes made from them. The effects are diarrhoea, vomiting and fever.
- Campylobacter: mainly in raw poultry meat. Campylobacter is one of the most common bacterial causes of diarrhoea. Even a few germs can make you ill.
- EHEC (enterohaemorrhagic E. coli): in raw beef and minced meat, raw milk and unwashed vegetables. In children it can cause severe kidney damage.
- Listeria: it multiplies even at fridge temperature. It occurs, for example, in smoked fish, raw-milk cheese and sliced cold meats. It is especially dangerous for pregnant women, older people and people with a weakened immune system.
- Noroviruses: viruses that are very infectious. They cause severe diarrhoea and vomiting. They spread through hands, vomit, surfaces and sometimes through raw shellfish, salad or frozen berries.
- Hepatitis A virus: spreads through hands and food and is a reason for an activity ban under the IfSG.
- Staphylococcus aureus: lives on skin, in the nose and in wounds. In food, the bacterium forms a heat-stable toxin. If you put it on food after cooking, you can make the food dangerous.
- Bacillus cereus: forms spores and is often found in rice, pasta and sauces that stand for a long time warm or at room temperature.
- Clostridium perfringens: multiplies in large portions of meat dishes that cool slowly or stand lukewarm for a long time.
Who is at particular risk?
Infants and small children, pregnant women, older people and people with existing illnesses or a weakened immune system are at particular risk. This is why especially strict rules apply in nurseries, schools, hospitals, care homes and catering for parties.
Perishable food
Perishable foods spoil quickly or become dangerous if they are not chilled or handled correctly. Examples: meat, poultry, fish, eggs and egg products, milk and dairy products, salads, delicatessen products, sauces, cooked rice, filled rolls and cakes with cream or custard.
How germs get onto food
- through unwashed hands,
- through raw food that touches other food,
- through equipment, boards and cloths,
- through ill staff,
- through pests such as flies, cockroaches and mice,
- through contaminated water or unwashed fruit and vegetables.
Key points
- Dangerous food often looks normal.
- Bacteria need warmth, moisture, nutrients and time. Cold slows them down, heat kills them.
- Some toxins survive cooking.
- Listeria grows even in the fridge.
- Handwashing, keeping raw and ready-to-eat food apart, and healthy staff are the best protection.