Each year it is estimated that as many as 5.5 million people in the UK may suffer

from foodborne illnesses – that’s 1 in 10 people. This section explains what food

poisoning is and describes some of the most common germs that cause it.

More information on this can be found from the Food Standards Agency website –

‘www.food.gov.uk’.

Germs are invisible except under a powerful microscope; hence the name microorganisms

or microbes. Microbes can be grouped according to their different

structures; two common groups of microbes are viruses and bacteria. Not all

bacteria are harmful – indeed many are essential for life. The bacteria, viruses and

other microbes that cause illness are commonly known as germs.

Germs found in food can lead to food poisoning which can be dangerous and can kill

– though this is rare. They are very hard to detect since they do not usually affect the

taste, appearance or smell of food.

The most serious types of food poisoning are due to bacteria. The more bacteria present,

the more likely you are to become ill. Bacteria multiply fast and to do so need moisture,

food, warmth and time. The presence or absence of oxygen, salt, sugar and the acidity of

the surroundings are also important factors. In the right conditions one bacterium can

multiply to more than 4 million in just 8 hours.

temperatures some bacteria will die, but many survive and can start to multiply again

if warm conditions return. That is why proper cooking and chilling of food can help

reduce the risk of food poisoning.

Germs can get into our food at any point in the food chain – from the time when an

animal or food is in the field to the moment food is put on to the table to eat.

If they are allowed to survive and multiply, they can cause illness when that food is

eaten.

Sometimes these germs are spread to other foods, for example via hands, or kitchen

utensils and cause illness when those foods are eaten. This is known as crosscontamination.

The symptoms of food poisoning can last for days and include abdominal pains,

diarrhoea, vomiting, nausea and fever. The symptoms usually come on suddenly, but

can occur several days after eating contaminated food. They will usually get better on

their own. Your pharmacist may be able to advise on suitable remedies or contact

NHS Direct. If symptoms persist contact your doctor. Symptoms such as diarrhoea

and vomiting are not always due to food poisoning but if you think you have food

poisoning contact your local Environmental Health Officer (see below).

Sometimes groups of people can be infected at the same time. They may have eaten

at a party, or restaurant or there may be a batch of contaminated food being sold in

different places. In such cases Environmental Health Officers (EHOs), who are

employed by Local Authorities, will usually investigate the matter to find out the

cause. EHOs will alert others to the dangers, offer advice, and where necessary

prosecute offenders for breaches of food safety laws. Whenever such outbreaks of

food poisoning occur or are suspected, it is important to contact an EHO; they can be

found in the local council section of the phone book.

EHOs are also happy to provide advice on food safety to local businesses. Another

source of advice is the Food Standards Agency, their website address is

‘www.food.gov.uk’.

Food poisoning is more likely to affect people with lowered resistance to disease

than healthy people who might show mild symptoms or none at all. Elderly or sick

people, babies, young children and pregnant women are particularly vulnerable to

food poisoning. Seek treatment if they have symptoms. Extra care should also be

taken when preparing food for, and looking after, these vulnerable groups to

minimise the risks of their coming into contact with food poisoning bacteria.

Most food poisoning is preventable although it isn’t possible to completely eliminate

the risk. For further advice see our other fact Files on Food Storage, Food Hygiene

and Food Preparation.

Here is some more information about the most common microbes that cause food

poisoning. More information on this can be found from the Food Standards Agency

website – ‘www.food.gov.uk’.

Source: Campylobacter can be found in raw poultry and meat, unpasteurised milk,

and untreated water. Pasteurised milk can be contaminated by birds pecking bottle

tops on the doorstep. Pets with diarrhoea can also be a source of infection.

Campylobacter is the most common identified cause of food poisoning.

Characteristics: Illness may be caused by a small number of bacteria. Crosscontamination

can lead to illness. Thorough cooking and pasteurisation of milk will

destroy Campylobacter.

Symptoms: Symptoms include fever, headache and a feeling of being unwell,

followed by severe abdominal pain and diarrhoea which may be bloody. Symptoms

normally take 2-5 days to appear but it can be as long as 10 days and return over a

number of weeks.

Source: Salmonella has been found in raw meat, poultry and eggs, raw unwashed

vegetables, unpasteurised milk and dairy products and many other types of food. It is

found in the gut and faeces of animals and humans. Salmonella is the second most

common cause of food poisoning.

Characteristics: Salmonella survives when refrigerated although it is unable to

multiply through cooking and pasteurisation. Usually large numbers of the bacteria

are needed to cause infection but outbreaks have been reported where infection has

been caused by a low number of bacteria.

Symptoms: It normally takes 12 to 48 hours for symptoms to develop. Symptoms may

include fever, diarrhoea, vomiting and abdominal pain. Infection may be very severe,

and in some cases may be fatal. It is particularly likely to cause severe illness in the

very young and very old. Symptoms may last up to three weeks and there may be

complications such as reactive arthritis.

Source: E. coli is a widespread organism that is normally found in the guts of animals

and humans. There are many different types, some of which are capable of causing

illness. One uncommon type which can cause serious illness is Verocytotoxin

producing E. coli O157 which has been found in raw and undercooked meats,

unpasteurised milk and dairy products, raw vegetables and unpasteurised apple

juice.

Characteristics: Illness may be caused by a small number of bacteria, so crosscontamination

can lead to illness. The bacteria can survive refrigeration and freezer

storage, but thorough cooking of food and pasteurisation of milk will kill them.

Symptoms: Symptoms normally take about 2 days to develop but may start within a

day, or take up to 5 days to come on. The main symptom is diarrhoea. In some cases,

particularly in children under the age of 6 and in the elderly, infection can lead to

diarrhoea which may be bloody and severe, kidney failure, and sometimes death.

Source: Clostridium perfringens is excreted by a wide range of animals. It can be

found in soil, animal manure, and sewage, and also in raw meat and poultry.

Characteristics: Clostridium perfringens produces spores which may not be killed

during cooking. If foods are allowed to cool slowly, the spores germinate and

produce bacteria which grow rapidly. These bacteria may not be killed if the food is

not reheated until it is piping hot. It is particularly associated with gravies, cooked

meat dishes, stews and pies and very large joints of meat and poultry.

Symptoms: Symptoms are mainly abdominal pain, diarrhoea and sometimes nausea

starting usually 8-18 hours after eating the food. It may be fatal in the elderly and

debilitated.

Source: Listeria is widely present in the environment. It is found in soil, vegetation,

raw milk, meat, poultry, cheeses (particularly soft mould-ripened varieties) and salad

vegetables. It is also found in the guts of animals and humans. One type, Listeria

monocytogenes, can cause illness in humans.

Characteristics: Listeria monocytogenes, unlike most other food poisoning bacteria,

can grow at low temperatures, even in the fridge. Thorough cooking of food and

pasteurisation of milk will destroy Listeria.

Symptoms: It can take days or weeks for symptoms to develop. Symptoms can range

from mild flu-like illness to meningitis and septicaemia; and in pregnant women,

abortion, miscarriage or birth of an infected child. Other susceptible groups are

those whose immune systems are compromised, the very young and the very old.

People in these groups are advised to avoid certain foods, such as soft mouldripened

cheeses and pâtés, because of the risk of severe infection.

Source: Bacillus cereus is found in soil and dust. It is frequently found in rice dishes,

occasionally pasta, meat or vegetable dishes, dairy products, soups, sauces and

sweet pastry products where these have not been cooled quickly and effectively after

cooking and during storage.

Characteristics: Illness may be caused by a small number of bacteria, so crosscontamination

can lead to illness. The bacteria can form spores; they are not easily

destroyed by heat and will survive cooking of food. If food is cooled slowly or kept

warm for some time before serving, the spores will germinate and produce bacteria.

Bacteria can multiply rapidly at these temperatures and produce a very heat

resistant toxin which will not be destroyed by subsequent reheating.

Symptoms: Bacillus cereus can cause two distinct types of illness - a diarrhoeal form

(diarrhoea and abdominal pain) with an incubation period of 8 to 16 hours and an

emetic form (primarily vomiting, possibly with diarrhoea) with an incubation period of

1 to 5 hours. In both types the illness usually lasts less than 24 hours after onset.

Source: Staphylococcus aureus may be found on the skin, in infected cuts and boils

and in the nose. It may also be found in unpasteurised milk. It can be transferred to

food from the hands or from droplets from the nose or mouth.

Characteristics: Food poisoning from Staphylococcus aureus follows the

consumption of heavily contaminated food, where bacteria have multiplied and

produced a toxin which causes illness when the food is consumed. Staphylococcus

aureus survives when refrigerated although it does not multiply. The bacteria is

destroyed by pasteurisation of milk and cooking of food, but the toxin may survive

these processes. The main foods associated with illness are cooked meats, poultry

and foods which are handled during preparation without subsequent cooking.

Symptoms: Onset of symptoms varies between 2 and 6 hours. Symptoms are severe

vomiting, abdominal pains and diarrhoea. They generally last no longer than 2 days.

(Previously know as Small Round Structured Viruses or SRSVs)

Source: Norwalk-like viruses are the commonest foodborne viral infection and are

usually spread from person to person.

Characteristics: Norwalk-like viruses are transmitted from person to person (eg by

projectile vomiting), environmental contamination and contaminated water.

Foodborne infection may be associated with sewage contamination of shellfish or

fresh produce, or contamination by an infected food handler. Outbreaks occur most

frequently in nursing homes and hospitals due to person to person spread.

Symptoms: Norwalk-like viruses cause an acute gastro-enteritis and are the

commonest cause of viral gastro-enteritis epidemics. Symptoms include vomiting

and diarrhoea. The symptoms take 12-48 hours to develop, and last for about 2 days.

Here is some more information about the incidence of food poisoning in the UK

Source: Health Protection Agency Centre for Infections/Communicable Disease

Surveillance Centre, Health Protection Scotland and Communicable Disease

Surveillance Centre Northern Ireland

* denotes provisional figures.

Source: Health Protection Agency Centre for Infections/Communicable Disease

Surveillance Centre

* denotes provisional figures

Source: Health Protection Scotland

* denotes provisional figures.

Since 1995 figures include reported cases of Campylobacter.

Source: Communicable Disease Surveillance Centre Northern Ireland

* denotes provisional figures