What is foodborne illness?
Foodborne illness (or food poisoning) is any illness caused by or thought to be caused by consumption of contaminated food (or water). The food may be contaminated with bacteria, viruses, parasites or toxins.

A.    Bacteria causes:

B.    Viral  Causes:

C.    Parasitic  Causes:

D.    Intoxications:

  • Bacillus Cereus intoxication
  • Staphylococcus aureus intoxication
  • Clostridium botulinum intoxication (botulism)
  • Marine biotoxins Including shellfish toxins (Paralytic shellfish poisoning [PSP], Neurotoxic shellfish poisoning [NSP], Diarrheal shellfish poisoning [DSP], Amnesic shellfish poisoning [ASP],
  • Mycotoxins (aflatoxin and ochratoxin)

How does foodborne illness come about?
Foodborne illness comes about when a series of conditions are favourable to allow spread and multiplication of pathogens, especially bacteria. When someone eats a piece of contaminated food, the larger the dose of bacteria the more likely they are to become ill and if the dose is very large or they are a vulnerable person and inadequately equipped to fight off infections (such as a small child, a debilitated elderly adult, someone who has recently had extensive surgery or someone living with cancer), then the large dose of bacteria can overcome the person's natural defences and produce illness, frequently severe and occasionally fatal.  

Dose: Salmonella, under optimal conditions replicates every 20 minutes. Over 24 hours a single cell of salmonella can multiply and produce 2 x 1021 descendants (that is 2 thousand billion, trillion descendants in one day)
Temperature: bacteria thrive in warm conditions (the ideal for most is 38-450C). Many can replicate (albeit more slowly) at lower temperatures - listeria can replicate at temperatures down to 30C.
Nutrition: bacteria drive nutrition for the environment and foods eaten by man often provide them with high quality nutrition especially meat and dairy produce.

Viruses behave slightly differently. They do not replicate on food so they do not increase in number sitting on a piece of ham the way a bacterium can. Instead they replicate within the living cells of the person who has eaten the food contaminated with the viruses. Many foodborne illnesses are notifiable diseases in Ireland. 

What are the symptoms of foodborne illness?
The symptoms of foodborne illness vary depending on the pathogen. The commonest syndrome (collection of clinical features) seen with bacteria is gastroenteritis which is characterised by nausea, vomiting, diarrhoea. Occasionally abdominal cramps, fever and headaches can occur. Typhoid and paratyphoid tend to produce fever, aches, constipation, and flu like symptoms. Diarrhoea is much less common. Viruses tend to produce vomiting rather than diarrhoea and protozoa tend to produce diarrhoea with heavy watery diarrhoea, but symptoms can vary widely. Intoxication can produce a wide range of symptoms from flu like illness to muscle weakness and paralysis, depending on the toxin.

Fortunately, most forms of food poisoning last only a short time - between one and three days. However you may feel sick for as long as seven or more days. In extreme cases food poisoning can be fatal.

How is food poisoning managed?
Most cases of food poisoning are simple short-lived illnesses and do not require any treatment. Antibiotics and anti-diarrhoeal medication are not necessary for cases of food poisoning. Very rarely a severe case of bacterial infection (e.g. typhoid) will require antibiotics but this is the exception. Drinking plenty of fluids, rest and small bland meals are the best approach. Some episodes of illness can last a number of days. Salmonellosis, cryptosporidiosis, VTEC and campylobacterosis generally last for a week, so do not expect it to resolve in a day or two; it is uncommon that bacterial food poisoning would resolve quite that quickly. The following are worrying features - if you notice any of these you should discuss with your GP:

  • If the patient cannot keep any food or fluids down
  • If their diarrhoea is very heavy
  • If they have blood in their stool
  • If small children become floppy or unresponsive
  • If adults become poorly responsive
  • If the patient begins to stop passing water

How can food poisoning be prevented?
The following are the best methods to prevent food poisoning: 

  • Handwashing: always wash your hands with soap and running water and especially:
    • After using or cleaning the toilet
    • After attending to anyone with diarrhoea or vomiting
    • After touching anything contaminated by diarrhoea or vomiting
    • After handling contaminated clothing or bedding (including nappies)
    • After handling household and garden waste or rubbish
    • After touching or handling pets or other animals
    • On returning to the house having been working in the garden or on the farm
    • Before handling, preparing, serving, or consuming food or drink

Here is a simple poster showing handwashing technique.

  • Cleaning: utensils and surfaces should be kept clean at all times especially if before being used to prepare food and if anyone in the house is sick
  • Cooking: food should be cooked properly and according to the manufacturer's instructions
  • Prevent cross contamination: raw and cooked (ready to eat) food must be kept separate - juices from raw food should not be allowed to drip on cooked food in a fridge
  • Refrigeration: cooked and raw food must be kept in the fridge - this is especially true for meat and dairy produce. Ensure your fridge is working properly. Five degrees Centigrade is the temperature that food should be stored at in the fridge.

Further information on storing and preparing food can be found on the website of safefood.

Updated 6th July 2010