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What causes a food poisoning?

Food poisoning is caused by eating food or drinking something that has been contaminated with either bacteria, a virus or a parasite.

Bacteria that causes food poisoning

  • Salmonella

    Salmonella is probably the most well-known type of bacteria. There are over 2,500 strains of it and it is found in undercooked or raw meat, as well as in unpasteurised milk and dairy products and raw eggs. You can also get it by eating fruit or veg that have been in contact with manure from an animal that is carrying the bacteria.

    The incubation period, which is how long it takes between you eating the contaminated food and becoming ill, is 12 to 72 hours and symptoms can last from four to seven days.

    Usually, it is not too severe, but it can cause serious illness in older people, babies and people with long-term conditions, and you are more likely to need hospital care if this is the case.

  • Campylobacter

    Campylobacter bacteria causes most food poisoning cases in the UK – according to the Food Standards Agency, there are around 280,000 cases of this type of food poisoning every year.

    The bacteria can be found in under-cooked or raw meat - poultry in particular, like chicken or turkey. It is killed by heat, so it is important that you thoroughly cook these types of food.

    It can also be found in untreated water or in unpasteurised milk. It is commonly picked up in this way abroad, so make sure any ice cubes you have in your drinks are made from treated water, and use bottled water to clean your teeth, wash fruit, etc.

    The incubation period is usually two to five days and symptoms last under seven days.

  • Escherichia coli (E. coli)

    Most strains of E. coli will not do you any harm, but some, including the E.coli O157 strain, can make you very poorly. The bacteria is found in undercooked beef, particularly in meatballs and burgers, as well as in raw leafy veg and unpasteurised milk.

    The incubation period is one to eight days and symptoms last between a few days and a week.

  • Listeria

    This is rare but can be very dangerous if you are in an at-risk group, such as the elderly, if you have a weakened immune system, are pregnant, or the very young, including babies.

    The bacteria are found in chilled (it can survive very cold temperatures), pre-packed foods, such as soft cheeses, sandwiches, pate and cooked sliced meats, particularly when past their ‘use by’ date.

    The incubation period is between a few days to a few weeks and symptoms last for around three days.

  • Botulism

    This is very rare but very serious, and is found in food that has not been properly canned, preserved or cooked.

    The incubation period ranges from 12 – 72 hours in adults, and 3 – 30 days in children. It affects your nerves, so it is very important you seek medical treatment as soon as possible.

  • Shigella

    Shigella bacteria can be passed in contaminated food, can affect any food that is washed in contaminated water or it can even be picked up by swimming in contaminated water.

    The incubation period is within seven days and symptoms can last up to week.

Viruses that cause food poisoning

Viruses are types of germs that are smaller than bacteria. The viruses that may cause food poisoning include:

  • Norovirus

    Norovirus, also known as the winter vomiting disease, can spread easily from one person to another, and through contaminated food and water. Any food that’s handled by someone carrying the virus can be contaminated.

    The incubation period of the Norovirus is one to two days and symptoms last for a couple of days. However, it can be dangerous for the very young and elderly

  • Rotavirus

    Rotavirus is a common cause of food poisoning in babies and children, and it can quickly lead to dehydration, which may cause hospitalisation. Adults can also be affected, but the symptoms will not usually be as severe.

    It is often passed from touching something that has been contaminated but can also be caught from contaminated food.

    The incubation period is within one week and symptoms may last for five to eight days.

Parasites and food poisoning

If you have recently returned from a developing country and have food poisoning, it may be because you have picked up a parasite, although this is rare.

The contamination period can be up to 10 days, although it can sometimes take weeks for symptoms to appear. It will need treatment, so see a GP if you believe this could be the cause of your illness.