Cause

Food-borne illnesses are caused by microorganisms found in primary food products (before processing) or present after environmental contamination (e.g. contact with contaminated surfaces, asymptomatic but contagious person handling food, etc.). 

A lack of hygiene and failure to respect the hot/cold chain favour the growth of the microorganisms present in the food and their transmission to humans.

DID YOU KNOW? Microorganisms can be found in food without necessarily causing food-borne illnesses. To fall ill, several conditions must be met: a harmful microorganism, in sufficient quantity, in the “right” food and must be ingested by a sensitive person.

The foods most commonly responsible for a food-borne illness are:

• mixed dishes (vol-au-vent, beef stew)
• raw or undercooked meat 
• dairy products and products made from raw eggs (chocolate mousse, tiramisu, mayonnaise, unpasteurised milk)
• fruit and vegetables 
• raw or undercooked fish, shellfish and bivalve molluscs (clams, oysters, mussels, scallops).

DID YOU KNOW? Histamine is found in fish, nuts, meat and other food obtained by microbial fermentation (wine, sausages, marinades), can cause allergic symptoms (redness, itching, migraine, dizziness) and gastrointestinal disorders. Histamine is not destroyed when cooking fish. It is therefore very important to keep the fresh fish in refrigerated form (0-4°C) in order to minimise the formation of histamine.

• Salmonella (poultry, raw eggs, pork meat, beef, milk products) 
• Campylobacter (poultry, unpasteurised milk)
• Escherichia coli pathogen (raw beef, unpasteurised milk, cheese made from unpasteurised milk, germinated seeds)
• Bacillus cereus (rice, cooked pasta)
• Staphylococcus aureus (milk products, meat, cured meat, fish, custard) 

Food can be contaminated during production and preparation. For example:

• during slaughter and cutting, bacteria naturally present in the intestines of animals can contaminate carcasses of meat intended for food
• fresh fruit and vegetables can be contaminated when they are sprayed with substances contaminated by animal manure (water, slurry) or because of poor personal hygiene during harvesting 
• oysters and other bivalve molluscs may be contaminated with the Vibrio bacteria naturally present in seawater and other microorganisms such as the Norovirus in sewage discharged into seawater
• in the kitchen, microorganisms can be transferred from contaminated food to uncontaminated food when the same knife, the same board or another utensil are used without being washed between uses (cross-contamination).

The way in which food is stored can also promote the development of microorganisms. 

• A slightly contaminated food, if not kept in a cool or sufficiently cooked condition, can become highly contaminated.
• Some bacteria develop even in refrigerated conditions (Listeria) and other bacteria or toxins are resistant to cooking heat (C. perfringens, Staphylococcal enterotoxin, B. cereus emetic toxin).

Please note! Hands are an important vector of microorganisms. Infected persons, who may be asymptomatic, can contaminate food by neglecting hygiene rules when preparing food: for example, when not washing their hands before starting to cook, during preparation, after handling raw produce (in particular meat and eggs) and after leaving the toilet.