Food Poisoning Symptoms

Food Poisoning Symptoms, Causes, Diagnosis And Treatment

Food poisoning is a common problem that can make sufferers very ill, and while most cases generally resolve themselves, some can be so serious that they are ultimately fatal. Food poisoning symptoms usually involve vomiting and diarrhoea, and in many cases medical intervention is required. In general, the cause of food poisoning is food contaminated by bacteria or other toxins, and cases are mild and short-lived. We will have a look at the various bacteria concerned, as well as how to recognise food poisoning and what to do to treat and prevent it, during the course of this article.


The symptoms of food poisoning, as we have already mentioned, involve vomiting and diarrhoea, and this is because the condition affects the digestive system. There are other symptoms that may also occur, including:

The problems that occur come largely from dehydration, as the above symptoms – if suffered repeatedly – will result in significant fluid loss. This is why medical treatment may be required, especially in more severe cases.


A few facts about food poisoning before we go into more detail about the causes and treatment:

  • Food poisoning affects millions of people each year
  • Most cases are short-lived and quickly resolved without intervention
  • Poorly cooked or infected food can be the cause
  • Prevention is the key, with attention to hygiene and sensible cooking needed

The problems with food poisoning are many, but if you follow the guidelines offered in recipe books and such on how to cook different food you will find that you can steer clear of any problems. Now, let’s have a look at the causes of food poisoning.


It is important to understand that food poisoning can be caused by many different bacteria and conditions, and also that different types have different levels of severity. One important factor in diagnosing food poisoning is knowing the bacteria involved, as some have longer incubation periods than others. Let’s have a look, first, at those that incubate quickly, within less than 24 hours:

  • Staphylococcus Aureusthis common bacteria causes many cases of food poisoning every year, and those who eat food contaminated with it can become ill as little as one hour afterwards.
  • Bacillus cereusthis unusual bacteria is confined to cases of poorly cooked rice
  • Clostridium Perfringensnot a bacterium but a spore, it occurs where food has been stored in warm conditions, and causes serious diarrhoea within a few hours.

There are also a couple  of chemical forms of food poisoning – Scombroid and Ciguatera poisoning which are both associated with poorly cooked or stored fish – that manifest their symptoms very quickly, and we must not forget mushrooms, some of which can be fatal.

The following are types of food poisoning that may take up to three days to occur:

  • Campylobacterthe most common type of food poisoning, this bacterium causes millions of cases each year
  • Shigella responsible for cases of very serious dysentery
  • Salmonella a well known bacterial form of food poisoning associated with undercooked food such as chicken and eggs, it can be fatal in severe cases
  • Vibrio parahaemolyticusfound in shellfish but not common
  • E.colioften found in people who eat food abroad
  • Botulism – a severe case of botulism can be very dangerous indeed

These are just a few of the more well known causes of food poisoning. Now we move on to the longer incubation forms – these take anywhere between a week to a month – and we begin to find some of the more serious cases. We have split these into different sections so that you can see how food poisoning can differ in its cause:


  • Listeriafound in unpasteurised milk and dairy products, this can remain unnoticed for several weeks
  • Brucellosisanother bacterium associated with milk and dairy products, particularly goats milk


  • Trichinosisa worm found in undercooked pork and some game meat
  • Giardiasis contracted from water that has been contaminated by sheep and other animals
  • Cysticercosis found in overseas countries in contaminated water.

Viruses and other causes:

  • BSE – a prion that causes what we know commonly as Mad Cow Disease, which can manifest as vCJD in humans who eat contaminated meat
  • Hepatitis A – a virus spread by the poor handling of meat

There are numerous other less common causes of food poisoning, but what is important to remember is that all (with the possible exception of vCJD) are treatable.


Diagnosis of food poisoning is part physical and part questionnaire; if a patient complains of feeling unwell and admits to having eaten raw or undercooked food recently, or has travelled to places where hygiene is suspect then they will immediately point the doctor in the right direction. Certain symptoms are clear signs of food poisoning and make diagnosis even easier. Blood pressure tests and checks on the other vital signs may be carried out, and where bacterial infection is suspected stool samples may be required in order to determine which is involved.


While most cases of food poisoning will resolve themselves in no time at all, more serious cases many need further treatment. If a patient has suffered dehydration – and many do – they may need to be admitted to hospital to have fluids administered and be kept under observation. They may also be prescribed medication for nausea, vomiting and diarrhoea. Antibiotics will sometimes be prescribed, but in most cases are unnecessary as the illness will pass in due time.

How Long Does Food Poisoning Last?

You should be concerned if your suspected food poisoning symptoms last longer than two days, for this is the general period for the majority of cases. If symptoms persist, it is important that you contact your doctor right away for a full diagnosis as described above.

Can You Catch Food poisoning From An Infected Person?

The answer is no, you cannot; this is because the bacteria that cause food poisoning are not air-borne, and cannot be passed from person to person. You can only suffer from food poisoning thanks to ingesting contaminated food.

We hope that this article has helped you understand more about the many types and causes of food poisoning, and that you now know what to do should you suspect you are suffering from the symptoms that we have described.

Written By Jack Johnston

Jack Johnston, M.D., is board-certified by the American Board of Family Medicine. Dr. Johnston received his undergraduate degree from the University of Illinois at Champaign. In 1995 he graduated with a Medical Degree from the Stritch School of Medicine at Loyola University of Chicago. Dr. Johnston’s residency in Family Medicine was completed at Northwestern Memorial Hospital. After completing an Integrative Medicine Fellowship, Dr. Johnston served as Chief Resident in 2001.


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