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Food poisoning

What to do and how to prevent it

Food poisoning is an acute illness, which usually occurs within 1 to 36 hours of consuming contaminated or poisonous food. The symptoms can include vomiting, diarrhoea, abdominal pain, nausea and fever, which normally last between 1 to 7 days.

This page describes the causes of food poisoning, the symptoms to look out for and how to prevent it.

Causes of food poisoning

Each type of food poisoning has a characteristic incubation period (the time it takes from consumption to symptoms) and predominant symptoms depending on the cause.

Food poisoning may be caused by:-

• bacteria and their toxins
• viruses
• chemicals (e.g. insecticides and cleaning agents)
• metals (e.g. lead and mercury)
• poisonous plants and animals (e.g. deadly nightshade, toadstools, Japanese puffer fish)

Bacteria are the most common causes of food poisoning and usually an extremely large number of the bacteria are required to make people ill.

Viruses also cause cases of vomiting and diarrhoea. They do not multiply in food but a much smaller number is required to make people ill. Air-borne infection is common and can spread easily from person to person.

Food poisoning from chemicals is rare and usually results from accidental ingestion when poisonous chemicals are stored in unlabelled bottles or food is contaminated with chemicals or additives.

Metallic poisoning causes vomiting and abdominal pains and results from the contamination of food and drink by contact with metals.

Poisonous plants/animals are again a rare form of food poisoning, particularly in commercial premises.

The following table includes of the causes and symptoms:

Bacteria	Source	Incubation period	Symptoms and usual duration
Salmonella	Raw meat, poultry, eggs, unpasteurised milk, pets, terrapins, infected food handlers.	6-72 hours; usually 12-36 hours	Diarrhoea, vomiting, fever, abdominal pain 1-5 days
Campylobacter	Raw meat, poultry, raw/bird pecked milk, untreated water, pets.	1-11 days; usually 2-5 days	Abdominal pain, diarrhoea 2-5 days
Listeria mononctogenes	Found in environment, cattle, sheep, silage, unpasteurised milk products including soft cheeses, pates.	Variable; usually 4-21 days	Fever, affects central nervous system Variable
Staphylococcus aureus	Human nose, mouth, cuts and wounds.	1-7 hours; usually 2-4 hours	Vomiting, abdominal pain, diarrhoea, fainting 6-24 hours
Clostridium perfringens	Faeces of animal and man, soil (on vegetables), dust, sewage	8-22 hours; usually 12-18 hours	Diarrhoea, abdominal pain 12-48 hours
Bacillus cereus (toxin in food)	Cereal products, especially rice, spices, dust, soil.	1-5 hours	Vomiting, abdominal pain, some diarrhoea 1-2 days
Bacillus cereus (toxin in gut)	Cereal products, especially rice, spices, dust, soil.	8-16 hours	Diarrhoea, abdominal pain, some vomiting 1-2 days
Vibrio parahaemolyticus	Sea water, shellfish.	2-48 hours; usually 10-18 hours	Diarrhoea, abdominal pain, vomiting, fever 2-5 days
Escherichia coli (infective)	Animal origins – cattle, sheep, humans, sewage, meat & raw milk.	12-72 hours: usually 12-24 hours	Diarrhoea, abdominal pain, fever 2-3 days
Clostridium botulinum	Soil, meat, fish and vegetables	8 hours to 8 days; usually 12-36 hours	Central nervous system (difficulty breathing, double vision, nerve paralysis), diarrhoea, vomiting Variable can be fatal
Chemicals (e.g. metallic poisons, pesticides, etc)		Less than 1 hours	Vomiting, abdominal pain Possibly CNS depending on agent involved
Poisonous plants/animals		Less than 15 hours	Vomiting, abdominal pain Possibly CNS depending on agent involved
Norwalk / Noro Virus		24-48 hours	Vomiting, diarrhoea, abdominal pain 24-48 hours

Preventing food poisoning

Food poisoning can be prevented, but it rarely occurs because of a single mistake. It can occur if:

• high-risk food is contaminated
• bacteria multiply in the food
• bacteria survive within the food

Therefore to control these hazards and prevent food poisoning we must prevent contamination by:

• purchasing from reputable suppliers
• good hygiene standards (of rooms, equipment, people)
• minimise handling
• separation of raw and cooked food, including surfaces and utensils
• covering food
• well designed and constructed food rooms
• good pest control
• effective storage and disposal of waste
• effective cleaning and disinfection

Prevent multiplication by:

• keeping food cold below 5ºC or hot above 63ºC
• reducing the amount of time at ambient temperature (when bacteria like to multiply)
• cooling food quickly
• storing under the correct conditions (read the label)

Destroy by:

• thorough cooking (to at least 75ºC at the centre of the food)
• heat processing (pasteurisation, sterilisation or canning)

The Royal College of Physicians have produced guidance for infected food handlers that covers the occupational aspects of managment. The national guideline is accompanied by summary leaflets for employers, employees and healthcare professionals

The following guidance may advise you if you think you are suffering from food poisoning symptoms:

This page was last updated on 06 October 2008

• Ill health
• Food poisoning
• Notifiable infectious diseases
• Staying in hospital

See also

• Notifiable Infectious Diseases