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Salmonella (non-typhoidal)

Fact sheet N°139
Updated August 2013


Key facts

  • Salmonellosis, is one of the most common and widely distributed foodborne diseases, with tens of millions of human cases occurring worldwide every year.
  • Most cases of salmonellosis are mild, however, sometimes people die from salmonellosis. The severity of the disease may depend on host factors and the strain of salmonella.
  • Since the beginning of the 1990s, salmonella strains which are resistant to a range of antimicrobials have emerged and are now a serious public health concern.
  • Basic food hygiene practices, such as "cook thoroughly", is recommended as a preventive measure against salmonellosis.

Overview

Salmonellosis is one of the most common and widely distributed foodborne diseases and is caused by the bacteria salmonella. It is estimated that tens of millions of human cases occur worldwide every year and the disease results in more than hundred thousand deaths. For salmonella species, over 2 500 different strains (called "serotypes" or "serovars") have been identified to date. salmonella is a ubiquitous and hardy bacteria that can survive several weeks in a dry environment and several months in water.

While all serotypes can cause disease in humans, a few are host specific and can reside in only one or a few animal species, for example, Salmonella Dublin in cattle; and Salmonella Choleraesuis in pigs. When these particular serotypes cause disease in humans, it is often invasive and can be life-threatening. Most serotypes, however, are present in a wide range of hosts. Typically, such strains cause gastroenteritis, which is often uncomplicated and does not need treatment, but can be severe in the young, the elderly and patients with weakened immunity. This group features Salmonella Enteritidis and Salmonella Typhimurium, the two most important serotypes of salmonellosis transmitted from animals to humans in most parts of the world.

The disease

Salmonellosis is a disease caused by the bacteria salmonella. It is usually characterized by acute onset of fever, abdominal pain, diarrhoea, nausea and sometimes vomiting.  

The onset of disease symptoms occurs 6 - 72 hours (usually 12-36 hours) after ingestion of salmonella, and illness lasts 2-7 days.

Symptoms of salmonellosis are relatively mild and patients will make a recovery without specific treatment in most cases. However, in some cases, particularly in the very young and in the elderly patients, the associated dehydration can become severe and life-threatening.

Although large Salmonella outbreaks usually attract media attention, 60 to 80% of all salmonellosis cases are not recognized as part of a known outbreak and are classified as sporadic cases, or are not diagnosed as such at all.

Sources and transmission

  • Salmonella bacteria are widely distributed in domestic and wild animals. They are prevalent in food animals such as poultry, pigs, cattle; and in pets, including cats and dogs, birds and reptiles such as turtles.
  • Salmonella can pass through the entire food chain from animal feed, primary production, and all the way to households or food-service establishments and institutions.
  • Salmonellosis in humans is generally contracted through the consumption of contaminated food of animal origin (mainly eggs, meat, poultry and milk), although other foods, including green vegetables contaminated by manure, have been implicated in its transmission.
  • Person-to-person transmission through the faecal-oral route can also occur.
  • Human cases also occur where individuals have contact with infected animals, including pets. These infected animals often do not show signs of disease.

Treatment

Treatment in severe cases is symptomatic, electrolyte replacement (to provide electrolytes, such as sodium, potassium and chloride ions, lost through vomiting and diarrhoea) and rehydration.

Routine antimicrobial therapy is not recommended for mild or moderate cases in healthy individuals. This is because antimicrobials may not completely eliminate the bacteria and may select for resistant strains, which subsequently can lead to the drug becoming ineffective. However, health risk groups such as infants, the elderly and immunocompromised patients may need to receive antimicrobial therapy. Antimicrobials are also administered if the infection spreads from the intestine to other body parts. Because of the global increase of antimicrobial resistance, treatment guidelines should be reviewed on a regular basis taking into account the resistance pattern of the bacteria.

Prevention methods

Prevention requires control measures at all stages of the food chain, from agricultural production, to processing, manufacturing and preparation of foods in both commercial establishments and at home.

Preventive measures for Salmonella in the home are similar to those used against other foodborne bacterial diseases (see "Recommendations for food handlers" below).

Some animals can also pass the bacteria directly to people. The contact between infants/young children and pet animals (cats, dogs, turtles etc.) needs careful supervision.

National/regional surveillance systems are important means to detect and respond to salmonellosis and other enteric infections in early stages, and thus to prevent them from further spreading.

Recommendations for the public and travellers

  • Ensure food is properly cooked and still hot when served.
  • Avoid raw milk and products made from raw milk. Drink only pasteurized or boiled milk.
  • Avoid ice unless it is made from safe water.
  • When the safety of drinking water is questionable, boil it or if this is not possible, disinfect it with a reliable, slow-release disinfectant agent (usually available at pharmacies).
  • Wash hands thoroughly and frequently using soap, in particular after contact with pets or farm animals, or after having been to the toilet.
  • Wash fruits and vegetables carefully, particularly if they are eaten raw. If possible, vegetables and fruits should be peeled.
  • When travelling, refer to WHO's brochure A guide on safe food for travellers.

Recommendations for food handlers

  • Both professional and domestic food handlers should be vigilant while preparing food and should observe hygienic rules of food preparation.
  • Professional food handlers who suffer from fever, diarrhoea, vomiting or visible infected skin lesions should report to their employer immediately.
  • The WHO Five Keys to Safer Food serve as the basis for educational programmes to train food handlers and educate consumers. They are especially important in preventing food poisoning. The Five Keys are:
    • Keep clean.
    • Separate raw and cooked.
    • Cook thoroughly.
    • Keep food at safe temperatures.
    • Use safe water and raw materials.

Recommendations for producers of fruits and vegetables

The WHO "Five keys to growing safer fruits and vegetables" is an educational manual for rural workers, including small farmers who grow fresh fruits and vegetables for themselves, their families and for sale in local market. It provides them with key practices to prevent microbial contamination of fresh produces during planting, growing, harvesting and storing.

The five keys practices are:

  • Practice good personal hygiene.
  • Protect fields from animal faecal contamination.
  • Use treated faecal waste.
  • Evaluate and manage risks from irrigation water.
  • Keep harvest and storage equipment clean and dry.

WHO response

  • WHO promotes the strengthening of food safety systems, promoting good manufacturing practices and educating retailers and consumers about appropriate food handling and avoiding contamination. Education of consumers and training of food handlers in safe food handling is one of the most critical means to prevent foodborne illnesses including salmonellosis.
  • WHO strengthens and enhances the capacities of national and regional laboratories in the surveillance of Salmonella, the other major foodborne pathogens and antimicrobial resistance in Salmonella and campylobacter from humans, food and animals through the network called Global Foodborne Infections Network (GFN) .
  • WHO’s main tool to assist Member States in surveillance, coordination and response to outbreaks is the use of the International Network of Food Safety Authorities (INFOSAN) . which links national authorities in Member States in charge of managing food safety events. This network is managed jointly by FAO and WHO.
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For more information contact:

Food Safety Department
WHO/Geneva
Fax: +41 22 791 48 07
E-mail: foodsafety@who.int