Infections with bacteria in the genus Salmonella are the second most common cause of foodborne illness in Europe. They cause gastroenteritis that can sometimes be acute, but in some susceptible populations they may have more serious effects. This article presents salmonellosis and ways of preventing the disease.
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Updated on 18/12/2017
Disease, causative agent and role of ANSES
Salmonellosis: facts and figures
In Europe, bacteria of the genus Salmonella represent the most common cause of foodborne illness outbreaks (FIOs) and the second cause of foodborne illness. In France, Salmonella is the leading pathogen confirmed in foodborne illness outbreaks. In 2015, it accounted for 48% of outbreaks in which a pathogen was confirmed.
However, the number of outbreaks in which these bacteria are isolated has decreased constantly in the European Union since 2001. This improvement demonstrates the effectiveness of European policy in the areas of health and safety on livestock farms and in slaughterhouses, i.e. systematic slaughter of all laying hens on contaminated farms, and hygiene measures throughout the production chain.
Infection with these bacteria results in gastroenteritis that can sometimes be acute, which generally resolves spontaneously within a few days. However, the consequences can be serious in certain people with particular susceptibility, specifically:
- malnourished individuals
- people with certain diseases, such as achlorhydria, hypochlorhydria or neoplastic disease, or those taking antacid treatments
- patients taking broad-spectrum antibiotics.
Lastly, in infants and individuals with weakened immune systems (autoimmune disease, immunosuppressive disease, medical immunosuppressant treatment, etc.), an infection with Salmonella can become very serious, or even fatal.
The causative bacterium
Animals are the main reservoir for Salmonella. These bacteria can be found in the digestive tract of mammals (swine, cattle) and birds (domestic poultry) without causing symptoms in these animals. Some strains are also found in cold-blooded animals like reptiles and tortoises, or in aquatic species like molluscs and fish.
Salmonella present in the faeces of animals may contaminate grazing land, soil and water, and remain in these environments for several months. The environment and untreated water may therefore also be a source of contamination.
Contamination in humans usually takes place through contaminated food (95% of cases, mainly raw food), but also by contact with infected people or animals (including pets) or healthy human carriers (people who are contaminated but who show no symptoms). The foodstuffs most commonly implicated are eggs and raw-egg-based products or food that has not undergone sufficient heat treatment, such as dairy products (raw milk, mildly heat-treated milk, or milk that has become recontaminated during the manufacture of powdered milk), as well as undercooked meats (beef, pork, and poultry). However, cases described in the literature also point to a number of other foods (raw fruit and vegetables, shellfish, etc.).
A few simple hygiene measures in the home can reduce the risk of microbial contamination. It is essential to:
- wash hands well after contact with living animals and, for susceptible individuals such as immunodepressed subjects, infants and pregnant women, avoid contact with pet reptiles.
- wash hands well after handling raw foods (eggs, meat, vegetables, for example), and carefully clean work surfaces used to prepare these raw foods.
- cook food thoroughly, especially pork and poultry, as well as minced meat.
- store eggs at a stable temperature, avoid warm/cold fluctuations that facilitate condensation and penetration of pathogens (including Salmonella) through the shell to the inside of the egg.
- avoid washing eggs before storing them since this weakens the eggshell and may promote penetration of microorganisms (the same phenomenon as condensation).
- consume dishes using raw eggs such as mayonnaise, pastry cream or custard, chocolate mousse, pastries, etc. as close as possible to the time of preparation. If these items are stored, they need to be kept refrigerated, and then consumed within 24 hours.
Lastly, it is recommended that the elderly, people who are ill or immunodepressed, young children, and pregnant women avoid consuming raw or undercooked eggs, raw or undercooked meat, and raw milk.
Role of ANSES
As part of the national surveillance system, the ANSES Ploufragan-Plouzané Laboratory, which acts as National Reference Laboratory (NRL), is tasked with collecting data on contamination with Salmonella spp. isolated in France from infected or healthy carrier animals, their farming environment, the slaughterhouse environment, processing facilities for food of animal origin, and from food and feed.
In addition, the ANSES Laboratory for Food Safety in Maisons-Alfort organises and coordinates an epidemiological surveillance network known as the Salmonella Network. Made up of public and private volunteer laboratories, the network maintains a database on Salmonella of animal, food and environmental origin. Each year, this surveillance tool is used to collect biological and epidemiological data on nearly 15,000 strains. These data are used primarily to investigate foodborne illness outbreaks in order to identify the food source causing human contamination as quickly as possible.
Furthermore, concerning assessment of the risks related to bacteria in the genus Salmonella, the Agency, via its Risk Assessment Department and Expert Committee (CES) on Assessment of the biological risks in foods, has published many opinions and reports, including some on assessment of the health risks associated with Salmonella in food, surveillance methods for these pathogens in the food chain, and control measures on farms (chickens, hens, turkeys, etc.).