Guide Infectious disease and food poisoning

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1. Food poisoning

Food poisoning is a term used to cover an unpleasant range of illnesses which can be caused by bacteria, viruses, protozoa, chemicals, metals and poisonous plants.

To investigate potential food poisoning, we need to know what people are suffering from. We usually need a faecal sample to be provided and analysed to identify the cause.  

Viral food poisoning

Some viruses can cause vomiting and/or diarrhoea which can appear to be food poisoning - although the virus is actually caught from infected people in the same way a cold can be passed from person to person. This, strictly speaking, is not food poisoning. These are usually quite severe bouts of illness but recovery is normally within 48 hours, after which a person may still be a little weak for a day or so.

Bacterial food poisoning

Bacterial contamination can cause food poisoning. Illness usually starts between 12 and 36 hours after eating affected food. Symptoms can include headache, diarrhoea, nausea and vomiting and usually persist for between one and seven days - and rarely for much longer.

Protozoan food poisoning

Some infections can be caused by tiny free living animals called protozoa, such as Cryptosporidia or Giardia. These tiny animals are often found in untreated water supplies and raw milk. They live and multiply in the digestive system, irritating the lining and causing pain, fever and diarrhoea. Symptoms may appear and disappear for several weeks.  

Chemical food poisoning

Some foods may have high levels of chemicals or metals which could be naturally occurring from the growth of the organism or from contamination during transport or preparation. Some foods such as oily fish can develop high levels of histamine if not stored properly. These forms of poisoning tend to cause rapid vomiting, fever, tingling and can cause swelling of tissues. Severe symptoms require immediate medical attention. 

How to control bacterial causes of food poisoning

Food poisoning is caused by bacteria entering the body through the mouth on unwashed hands, infected food or drink. Most food poisoning bacteria multiply in food, some can multiply in the body, causing illness.

A person with diarrhoea can quite easily spread germs if they do not take particular care with their personal hygiene.

People with diarrhoea and vomiting symptoms are the greatest risk. Once the symptoms have gone for more than 48 hours, the chances of spreading the infection are greatly reduced. Anyone who has diarrhoea should avoid contact with others for this time.

If you have bloody diarrhoea you should tell your doctor as soon as possible. If the ill person is very young, very elderly, ill for more than two days or develops a fever, you should telephone your surgery for more advice.  

If you handle food or drink or are in contact with young children or elderly people in the course of your daily work, you should tell your employer or supervisor that you are, or have been, ill.

If you are ill, you should not prepare foods, or enter a food preparation area.

Thorough hand washing is vital:

  • after using or cleaning the toilet
  • after dealing with anyone with diarrhoea
  • after changing the baby’s nappy
  • after handling soiled clothing or bed linen
  • after handling raw meat

Regularly disinfect toilets, flush handles, taps and door handles in the immediate vicinity of the toilet.

Other precautions you should take

Cover open wounds or sores with a waterproof plaster.

Keep all perishable foods in a fridge separating raw meat from other foods.

Only take food out of the fridge just before use.

Keep fridge temperature below 5°C.

Ensure frozen foods are properly thawed before cooking.

Ensure foods are cooked thoroughly.

Keep kitchen surfaces and utensils perfectly clean. Wash them between preparing different foods.

Don't let pets or other animals in the kitchen when preparing food.

Don't wash pets food bowls with the family dishes.

Do not buy or eat food past its use by date.

Do not reheat food more than once.

Always follow the instructions on cooking/reheating microwave and ready meals carefully to ensure that the food is evenly heated throughout.

Discovering the cause of your illness

The only way to be sure what has caused a case of food poisoning is to take a faecal sample and detect the presence of the bacteria or virus responsible for the illness.

An Environmental Health Officer may visit and help you decide who needs to supply specimens. You will be given special bottles and packaging and asked to post them to the laboratory as soon as practical.

The results will be relayed to you as soon as they are available but in the meantime the Environmental Health Officer will be pleased to advise you further. Your help will reduce the risk of spreading the illness to others.

Treatment is not usually given for most types of food poisoning. It is simply a case of letting the body’s natural defences deal with the infection. In some cases antibiotics may be prescribed but such treatments can have the disadvantage of extending the time during which the patient carries the germs.