The WHO has declared that over 600 million people each year fall ill due to bacteria or viruses.

Is it true that food can transmit illnesses?

Yes. Food and water can contain bacteria, pathogenic microorganisms which contaminate foods if added accidentally or deliberately, and which can cause disease if they succeed in breaking through the body’s defences, especially in children and the elderly, or individuals with immune system compromise due to stress or illness.

How does contamination occur?

Bacteria may be present in foods at source, such as in meat from infected animals, or in vegetables grown in contaminated terrain or irrigated with contaminated water. Alternatively, foods can become contaminated during the various stages of processing, due to handling with dirty hands, contact with aerial secretions, using water not fit for drinking, or due to contact with contaminated foods.

How does food cause infection (food poisoning)?

These microorganisms become harmful through ingestion of food contaminated by the infectious agents (for example salmonella), or due to poisoning from toxins produced by the food itself (as in the case of botulism).

There are more than 250 types of food poisoning known throughout the world, with different symptoms and caused by different pathogens, mainly bacteria, viruses and parasites. New pathogens (the “emerging pathogens”, such as campylobacter jejuni, Escherichia coli 157:H7, Listeria monocytogenes, Yersinia enterocolitica, etc.) are being identified all the time, some of which are also spread by the increase in trade; the increased use of canteens, restaurants and eating out; travel, and large-scale industrial farming operations.

What are the most frequent illnesses, and what are their symptoms?

  • Botulism

An extremely serious type of food poisoning which occurs between 12 and 36 hours after eating contaminated food

Symptoms include dry mouth, muscle weakness, blurred vision, and difficulty swallowing.

Nausea or diarrhoea may also be present, but not always.

The foods responsible are fruit and vegetables prepared at home, sausages, more rarely tinned food.

  • Salmonellosis

Onset occurs 6 – 72 hours after eating contaminated food, with nausea, vomiting, diarrhoea, and fever.

The foods responsible are milk, eggs, meat and derivatives, and poultry.

  • Staphylococcus aureus

Symptoms are the same as those of salmonellosis, but occur between 30 minutes and 7 hours after consuming contaminated foods.

The foods responsible are milk, cream, unpasteurised cheeses, raw eggs (ice-cream, sauces) and undercooked meat.

  • Clostridium perfigens poisoning

Onset occurs 6 – 24 hours after eating contaminated food, with abdominal cramps and diarrhoea.

The foods responsible are meat, poultry, and fish prepared and then left at room temperature for a long time (improperly stored).

  • Bacillus cereus poisoning (poorly virulent)

Widespread in the environment, especially in soil.

This type of food poisoning causes abdominal cramps, 10-15 hours after eating contaminated food.

Foods containing rice, starchy foods, and foods stored at room temperature for a long time after cooking are the main culprits.

With the exception of botulism, the symptoms of food poisoning are the same as those of common ailments affecting the stomach and intestines.

Do not treat your symptoms by yourself – consult your doctor who will be able to prescribe the correct medicine when necessary.

How can food poisoning be prevented?


  1. Buy quality foods from trusted suppliers whenever possible.
  2. Check that the facilities are clean, the packaging is not damaged, check the expiry dates and ingredients.
  3. Avoid buying meat and fish from unrefrigerated displays. Check that frozen food packages are not wet or covered with frost or ice: this means that the cold chain has been broken (that the food has been allowed to thaw during transport or storage).
  4. Milk should be pasteurised, and fresh cheeses should be displayed in a refrigerator.


  1. If the product is not used immediately, it is best stored in the fridge for 3 to 5 days at 4°C.
  2. Wrap foods separately in aluminium foil or freezer bags to prevent them from coming into contact with each other.
  3. Fish should be stored in the coldest part of the fridge.
  4. Clean fridges regularly.
  5. Eggs should be washed. Do not use if the shell is broken.
  6. Food not intended to be eaten within a few days should be frozen for up to 6 months.


  1. Frozen meat or fish should be thawed in the fridge or the microwave. Avoid thawing foods at room temperature.
  2. Chicken should be well cooked, and pieces of shellfish that do not open should be thrown away. Sauces containing raw eggs should be put in the refrigerator immediately in sealed containers, and used as soon as possible.
  3. Do not prepare meat, fish and vegetables on the same work surface.
  4. Utensils should be thoroughly washed with soap and hot water.

The introduction of foods such as sushi and sashimi into the Western diet, along with the many new restaurants that offer this type of cuisine, means that the consumption of raw fish has increased greatly. Although there is little difference between raw and cooked foods in nutritional terms, from a hygiene standpoint the likelihood of ingesting bacteria or pathogens is much lower when food is well-cooked. Observing hygiene standards is necessary for all foods, but greater caution is required when preparing seafood.

Fish can be hazardous when eaten raw, because its intestines contain an extremely dangerous intestinal parasite known as anisakis.

However, this parasite is killed when the fish is immediately gutted and blast chilled, meaning that we can safely enjoy a dish of marinated anchovies, tuna carpaccio, or sea bass tartare.

Bivalve molluscs such as oysters have no intestine and therefore do not contain anisakis. Crustaceans too should only be eaten if they have been blast chilled.

But what is “blast chilling”?

Blast chillers are devices similar to a freezer, which rapidly chill foods to temperatures of between -20 and -40°C. Fish must be kept at these temperatures for a period ranging from a few hours to several days, depending on the blast chiller used and the temperatures involved. This is the only way to destroy the larvae. 

The greatest risks come from restaurants which do not observe the 2004 European regulation which obliges the use of blast chilling for all businesses which sell or serve raw fish.