Food can become contaminated at any stage during its production, processing or cooking.
For example, food poisoning can be caused by:
- not cooking food thoroughly (especially poultry, pork, burgers, sausages and kebabs)
- not storing food that needs to be chilled at below 5°C
- someone who is ill or who has unclean hands touching the food
- eating the food after it has passed its ‘use by’ date
- cross-contamination (the spread of germs such as E. coli from contaminated foods)
Cross-contamination
Cross-contamination is a cause of food poisoning that is often overlooked. It occurs when harmful bacteria are spread between food, surfaces and equipment.
For example, if you prepare raw chicken on a chopping board and do not wash the board before preparing food that won't be cooked or a ready-to-eat meal such as a salad, harmful bacteria can be spread from the chopping board to the food.
Cross-contamination can also occur if you store raw meat above ready-to-eat meals. The meat juices can drip on to the meals and contaminate them.
Sources of contamination
Food contamination is usually caused by bacteria. Some common types and their sources are described below.
Campylobacter
Campylobacter is the most common bacterial cause of food poisoning in England. Campylobacter bacteria are usually found on raw or undercooked meat (especially poultry), unpasteurised milk and untreated water.
Salmonella
Salmonella bacteria are often found in raw meat and poultry. They can also be passed into dairy products such as eggs and unpasteurised milk.
Listeria
Listeria bacteria may be found in a range of chilled ready-to-eat food including:
- pre-packed sandwiches
- pâté
- butter
- soft cheeses, such as brie, camembert or others with a similar rind
- soft blue cheese
- cooked sliced meats
- smoked salmon
Escherichia coli (E. coli)
Escherichia coli, known as E. coli, are bacteria found in the digestive system of many animals, including humans. Most strains are harmless but some strains can cause serious illness.
Most cases of E. coli food poisoning occur after eating undercooked beef (especially mince, burgers and meatballs) or drinking unpasteurised milk.
Viruses
The virus that most commonly causes gastrointestinal illness is the norovirus. This virus is easily transmitted from person to person, from contaminated food or water.
Infected people can contaminate food if they do not wash their hands properly after going to the toilet and then handle food.
Parasites
In England, food poisoning from parasites is rare. It is much more common in the developing world.
Toxoplasmosis is the most likely cause of parasitical food poisoning in England. It is caused by a parasite that is found in the digestive systems of many animals, particularly cats.
People can develop toxoplasmosis by consuming undercooked contaminated meat, or food or water contaminated with the faeces of infected cats.
