Diagnosing food poisoning

Confirming a diagnosis of food poisoning is not always as straightforward as it seems. Many of the symptoms of food poisoning are similar to those for other illnesses, for example ‘gastric flu’.

Another problem is if someone with food poisoning delays in seeking help or decides not to bother. This is often the case when someone has a mild form of food poisoning and decides to let it to resolve itself.

However, it is not easy to decide between seeking help for food poisoning or leaving it in the hope that it will get better on its own.

If you find that your symptoms are not easing, or have worsened in a short space of time; or you are the parent of a child with food poisoning who has become dehydrated then see your GP.

Questions your GP may ask you

Your GP will first of all, ask you about your symptoms. He or she will ask you a series of questions which may be similar to these:

• When did your symptoms first appear?
• How severe are they?
• Are they constant or do they come and go?
• Have they worsened?
• What types of foods have you eaten in the last 24 hours?
• Has anyone else in your family experienced the same symptoms? If so, did they eat the same foods as you?
• Are you passing blood?
• Do you have a temperature?
• Have you travelled to countries where there are poor standards of food safety? Have you drunk untreated water or been to places where water supplies are of dubious quality?
• Do you work in an environment where you may be contact with people who are already infected? This applies if you work in a care home, nursery or school.

Your GP will have your medical notes in front of him/herself so will be able to see if you have any current medical conditions which cause symptoms that are very similar to food poisoning.

If you have a weakened immune system due to cancer treatment, a transplant, HIV/AIDS or an autoimmune disease then he/she will have information about that.

Your GP will also examine you and if he/she feels that it is necessary, will refer you for tests.

Tests to diagnose food poisoning

These will include:

• Blood test
• Lumbar puncture
• MRI/CT scan
• Stool sample

A lumbar puncture is a procedure in which a small sample of fluid is removed from your spinal cord for further analysis. This fluid is known as ‘cerebrospinal fluid’which acts as a form of protection for your brain and spinal cord.

Some types of food poisoning result in the infection spreading beyond the gastrointestinal tract and into the bloodstream. If these bacteria or toxins get into the bloodstream then they can affect any part of the body, for example the brain or nervous system.

So, a lumbar puncture will be able to show if this has occurred. A small sample of cerebrospinal fluid is drawn off from the spinal cord via a hollow needle before being sent for analysis.

MRI/CT scans are only performed if doctors suspect that your food poisoning has spread to other parts of your body.

A stool sample is a procedure whereby you are asked to provide a small sample of your faeces for laboratory analysis. This analysis is conducted under a microscope and is designed to check for the presence of bacteria, viruses, parasites or toxins which are the cause of your food poisoning.

Specific tests to diagnose food poisoning

There are tests which are highly specific and are only performed if your GP suspects that you have a serious form of food poisoning, e.g. botulism.

They include:

• Sigmoidoscopy
• Electromyography

Sigmoidscopy is a type of endoscopy (slim tube) which is inserted into the anus to determine the cause of bleeding or infection. This is useful in cases where someone is experiencing bloody diarrhoea or rectal problems caused by their food poisoning.

Electromyography is a test in which electrical impulses within the muscles are measured to see if there is damage caused by food poisoning. This is useful if a particular species of bacteria has caused food poisoning, for example clostridium botulinum.

Your GP will be able to confirm a diagnosis of food poisoning, and the type, which is then used to devise a treatment plan.