Salmonella

Salmonella Enteritidis, Salmonella Typhimurium

Changed on: 31.08.2021
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Animal disease categories: D E

Profile

Salmonella is the second most common food-borne pathogen causing diarrhoea in Austria. Infection occurs through ingestion of salmonella with food, especially poultry, eggs and egg products, meat and meat products, dairy products and ice cream (however, there is hardly any food in which salmonella has not been detected). Symptoms usually occurs only if relatively large quantities of bacteria (more than 100,000) are ingested. This "starting number" is easily reached if food is stored improperly, as salmonella can multiply exponentially at ambient temperature within a few hours.

Occurrence

Salmonellosis is a common diarrheal disease (including vomiting and abdominal cramps) and is caused by infection with bacteria of the genus Salmonella (S.). Across Europe, the two serovars S. Enteritidis and S. Typhimurium are the main causes of food-borne salmonellosis in humans. The pathogens of typhoid fever and paratyphoid fever (S. Typhi and S. Paratyphi) do not occur in Austria. These serovars can be found in tropical and subtropical countries with low hygiene standards and cause systemic infections with intestinal involvement.

Salmonellosis is spread worldwide and the transmission pathways of Salmonella are very diverse. Livestock can be infected via contaminated feed. In chickens, colonisation with salmonella is often hidden because the animals do not show symptoms. Entire flocks of laying hens can be infected and shed bacteria. Transmission of salmonella to the unlaid egg results in eggs carrying bacteria. If these eggs are not boiled sufficiently before consumption, they can pose a health risk to humans.

Salmonella grow in a temperature range of 10 to 47°C and are not killed by freezing. Heating to over 70°C for at least 15 seconds is considered to kill the bacteria.

Reservoir

Pets and livestock (especially poultry), wild animals (birds) and exotic reptiles

Mode of transmission

Salmonella are transmitted mainly by consumption of raw or insufficiently heated food of animal origin (eggs, poultry meat, meat from other animal species and raw milk). Home-made products containing raw eggs, such as tiramisu, mayonnaise, creams and ice cream, can also be contaminated with salmonella.

During food prearation, unheated or insufficiently heated meat (e.g. poultry meat, kebabs, minced meat, raw sausages) may be a risk if they come into contact with products that are not heated (e.g. potato salad). This transfer of bacteria to other food (cross-contamination) can also occur through not sufficiently cleaned utensils such as chopping boards, knives and towels or unwashed hands. In addition to kitchen hygiene, raw products need to be continuously cooled to prevent bacterial growth.

A small proportion of salmonellosis is caused by smear infections: unintentional ingestion of salmonella through contact with infected humans and animals or with objects contaminated with faeces. Exotic small animals (mainly turtles and iguanas) can also be pathogen reservoirs and a risk for smear infections. It is recommended to clean the hands thoroughly with soap and warm water after each animal contact.

Incubation period

6-72 hours, usually 12-36 hours

Symptoms

Symptoms may include nausea, diarrhoea, fever, vomiting, circulatory problems and abdominal cramps. The symptoms usually last only a few days. Often a mild or asymptomatic course of the disease occurs, which depends, among other things, on the amount of bacteria ingested and the immune status of the person affected. In older people, salmonellosis can quickly lead to a life-threatening condition due to the high fluid loss and the associated circulatory stress.

Treatment

Patients with gastro-intestinal complaints without other risk factors should only be treated with antibiotics in special cases, as this can prolong shedding of bacteria and bacteria may develop resistance to antibiotics. In most cases, balancing the water and electrolyte levels is sufficient.

Preventive measures

Food, especially meat, poultry, eggs or cream-filled pasta, should be stored at cold temperatures and thoroughly cooked before consumtion. After handling raw poultry meat, it is essential to wash your hands thoroughly before starting any other kitchen work. The defrost water of frozen meat should be drained into the sink and the sink should be rinsed with hot water. All work surfaces and equipment that have been in contact with raw poultry meat, other raw meat or raw eggs should be cleaned with detergent and hot water. Freshly prepared food, if not consumed immediately, should be cooled and stored in the refrigerator.

Persons suffering from salmonella must not handle food on a professional basis during the period of illness.

Situation in Austria

Human

In 2020, 721 laboratory-confirmed cases of illness were registered in the epidemiological reporting system (EMS, as of 28.01.2021), corresponding to an incidence of 8.1 cases per 100,000 inhabitants. Thus, Salmonella was again - after Campylobacter - the second most frequent reported cause of bacterial food poisoning in Austria.

From 2002 to 2016, the number of salmonelloses decreased by 83 % (2002: 8,405 first isolates; annual report of the Salmonella Centre 2002). This decrease in human salmonelloses was almost entirely due to a decrease in S. Enteritidis infections(2002: 7,459 isolates; 2016: 671 isolates). The increase in salmonelloses in 2019 compared to 2018 can be attributed to an Austria-wide outbreak caused by S. Enteritidis. The infections occurred mainly in Asian restaurants through the use of eggs containing Salmonella. In 2020, due to the SARS-CoV-2 pandemic and the associated measures, there was a massive decrease in the number of stool sample submissions and, as a result, in the isolation of Salmonella.

The spectrum of the most common Salmonella serovars in human cases has changed slightly in recent years. S. Infantis, which is the most common serovar in broilers, and the monophasic variant of S. Typhimurium (probable reservoir: pigs) and S. Coeln are becoming increasingly important alongside S. Enteritidis and S. Typhimurium.

Figure 1: Number of salmonelloses in Austria 2000-2020 (total, S. Enteritidis, other serovars)

Figure 2: Comparison of incidences of campylobacteriosis/salmonellosis

Food

In 2020, 5,306 samples were tested for Salmonella as part of the audit and sampling plan and in priority actions. They were detected mainly in meat and meat preparations from poultry (90 Salmonella isolates out of 516 poultry meat samples), including Salmonella Enteritidis 5 times and Salmonella Typhimurium 3 times.

Salmonella Infantis was isolated most frequently (69 times), 47 of which were in fresh chicken meat. In raw turkey meat, Salmonella was detected 6 times in 89 samples. Poultry meat samples accounted for 9.7 % of the total sample material tested for Salmonella, but 97.8 % of all Salmonella-positive samples were in this food category. Because of Salmonella, one ready-to-eat food and one precooked seafood product were harmful to human health. 36 samples were assessed as unfit for human consumption (1 time minced meat, 35 times raw poultry meat or raw poultry meat preparation). In addition to the audit and plan samples, 1,010 broiler carcasses were tested for Salmonella as part of the process hygiene inspections at slaughterhouses (self-monitoring). Thereby 269 positive were detected (60 S. Agona, 204 S. Infantis and 5 S. Thompson). On 140 turkey carcasses, one positive sample with 2 different serovars was identified(S. Typhimurium and S. Coeln).

Table 3: Foodstuffs tested in 2020

SamplesNumber of examinationspositive
Chicken carcasses1.010269
Chicken meat fresh22359
Turkey fresh896
Turkey carcasses1401
Meat and meat products (excluding poultry)9001
Table eggs1810
Fruit, vegetables, salads3180

Animal

For humans, animal foodstuffs represent the most important source of Salmonella infection. In order to record the significance of the reservoir of salmonellae, EU-wide uniform baseline studies have been carried out in various animal populations in recent years. These studies proved for Austria that poultry (eggs and poultry meat) play the most important role for Salmonella infections in humans and that all other tested animal species (except reptiles) are only rarely carriers of Salmonella.

Based on these studies, the EU has set maximum levels per year at which flocks of poultry may be contaminated with S. Enteritidis and S. Typhimurium, including the monophasic variant: This is 2 % for laying hens, 1 % for broilers and turkeys, and 1 % for parent flocks of chickens (in addition to S. Enteritidis and S. Typhimurium, S. Infantis, S. Virchow and S. Hadar also fall within the target here). In 2020, the specified targets were achieved in Austria for all other directions of poultry use, with the exception of turkeys.

An increasingly frequently detected serovar is S. Infantis: since 2016 as the third most important serovar in human diseases and as the most frequent serovar in poultry meat and broilers. This S. Infantis is mostly a multidrug-resistant variant, showing resistance to three classes of antibiotics: quinolones, sulfonamides and tetracyclines.

The salmonella control programme in the EU provides for the control of the most important salmonella serovars for humans in animal populations. This currently includes only the serovars S. Enteritidis and S. Typhimurium (including monophasic variant) in broilers, turkeys for fattening and laying hens, and S. Infantis, S. Virchow and S. Hadar in parent stock of chickens. As S. Infantis in chickens for fattening is not included in the serovars to be controlled, no financial support is foreseen throughout the EU for control measures such as possible vaccination or culling of flocks. Although all flocks are tested for salmonella before slaughter, if serovars other than the target serovars are detected, there are no legal consequences. However, more and more slaughterhouses are refusing to slaughter Salmonella-positive flocks at all. As a result, fattening herds are not slaughtered but culled. This S. Infantis strain has taken root in broiler flocks and is very difficult to eliminate from the houses despite thorough cleaning and disinfection measures.

In turkeys, the prevalence of Salmonella spp. has been reduced from over 10% to 2% since the control programme began in 2010. In 2020, Salmonella was found in only 10 flocks, six of which were target serovars (4 times S . Typhimurium, 2 times monophasic variant of S. Typhimurium), which is why the target set by the EU was missed.

Feed

Feed is subject to a permanent monitoring programme in Austria. In the course of the official controls, samples are taken both on farms and in warehouses, compound feed plants and trading companies. Both finished feed mixtures and individual components are officially examined. In 2020, Salmonella was detected in one out of 352 tested feed samples for farm animals (0.3%)(S. Senftenberg). Protein-rich extraction meals or cakes (by-products from the oil processing industry) are considered the most significant source of Salmonella. Through these, Salmonella can be introduced into the feed chain and contaminate the compound feed produced from them.In 2020, 42 pet food and dog chew samples were officially tested. In 7 of them(17%) 11 serovars were detected, in one sample four different serovars, in another sample two different serovars. Handling pet food, especially chew toys, poses a demonstrable risk to humans. It is therefore recommended to wash hands after feeding and playing with dogs or cats.

Figure 3: Number of pet food samples 2009-2020 and number of samples with Salmonella detection

Figure 4: Number of feed samples 2009-2020 and number of samples with Salmonella detection

Professional information

Human Medicine

Diagnostics

The pathogen is usually detected by culture from stool (faeces), but also from blood or pus. Testing for specific antibodies from blood is not conclusive.

The National Reference Centre for Salmonella at AGES in Graz does serotyping according to the White-Kauffmann-Le Minor Scheme for all salmonella detected in human and non-human samples in Austria. In addition, the most important serotypes for human infections S. Enteritidis and S. Typhimurium are differentiated by means of MLVA (Multi Locus Variable Number Tandem Repeats Analysis).

    Leitlinie personenbezogene Kontrollmaßnahmen bei lebensmittelbedingten Krankheiten (2.07 M)
    Teil1: Salmonellose (Salmonella non-typhi), Campylobacteriose
    download file  | open PDF

Veterinary Medicine

Salmonella infections can be detected in almost all animal species. Reptiles are particularly susceptible to latent infections with a broad spectrum of serovars.

Salmonellosis in cattle: S. Dublin is adapted to cattle, but other serovars can also cause infections with severe clinical pictures. Calves from the 2nd week of life are most susceptible. The predominant symptoms are diarrhoea, disorder of the general condition or pneumonia, which become milder with increasing age. However, cows can suffer from serious illness with diarrhoea, loss of milk and abortions.

Salmonellosis in pigs: adapted species are S. Choleraesuis and S. Typhisuis. Non-adapted serovars cause disease less frequently, especially when it comes to diarrhoea. Weaning pigs and young pigs up to 60 kg are affected, the infection usually progresses as a general disease with fever and lung symptoms, less frequently with diarrhoea. Abortions are possible.

Salmonellosis in sheep: S. Abortusovis is strictly adapted to sheep and is one of the most important abortion pathogens. An oral infection or an infection via the mating act is followed by a general septicaemia. A typical symptom is abortion in the 4th or 5th month of pregnancy, in addition there are puerperal complications and general diseases of all age groups. Non-adapted serovars cause latent infections and diarrhoea as well as abortions in sheep.

Salmonellosis in horses: S. Abortusequi is the adapted type; after oral infection or infection via mating, a general infection develops which can lead to abortion in the 4th month of pregnancy. Weak foals are also possible. Mares develop a resilient immunity after abortion. Not adapted serovars can lead to asymptomatic diseases with excretion of the pathogen or mild to severe diseases up to septicaemia.

Salmonellosis in dogs and cats: These animal species have a higher resistance to salmonella, there are no adapted serovars. Latent infections are usually observed, and if other favourable factors for diarrhoea are present, vomiting and fever can also develop.

Salmonellosis in chicken: S. Gallinarum is adapted to chickens, but can also occur in turkeys and some other bird species. Mammals are not susceptible. This serovar occurs in 2 biovars: Biovar Pullorum is the causative agent for pullorum disease and causes acute septicaemia in chicks up to the 3rd to 6th week of life. The biovar S. Gallinarum is the cause of the so-called fowl typhoid fever, which occurs mainly in older chickens. Infections with non-adapted types usually do not cause disease in chickens, but cause latent infections. However, these are an important source of food-borne infections and get a lot of attention. The most important serovar in this context in Austria is S. Enteritidis, followed by S. Typhimurium.

Salmonellosis in water fowl:  Water fowl are monitored as a potential source of infection for humans longer than chickens, therefore special rules for the consumption of duck eggs have long been in place. Living in stagnant water means that these animals have an increased risk of infection. Disease with diarrhoea and septicaemia are mainly found in young animals (keel disease: backstroke swimming of sick animals).

Feed producers

Salmonella in dust

Feed materials containing protein, such as soya, rapeseed or sunflower extraction meal, are considered a significant source of contamination for compound feed and compound feed plants. Salmonella is often found in feed in very low concentrations. However, low germ contents make the analytical detection of positive samples difficult.

Project SINS: Overview of the contamination rate in Austrian animal feed companies (single or compound feed)

Decontamination with organic acids

Salmonella in feed can cause enormous economic damage to the compound feed and agricultural businesses and the products are not marketable. The decontamination of salmonella in feed is permitted under feed law.

DEKONTAM study on optimal decontamination processes

    Empfehlungen Futtermittel (663 K)
    Empfehlungen zur Beherrschung von Salmonellen in der Futtermittelproduktion
    download file  | open PDF

    Heimtierfutterherstellung_pdf (145 K)
    Infoblatt zur Heimtierfutterherstellung
    download file  | open PDF

    Zusammenfassung SINS Studie (47 K)
    Staub als Indikator zum Nachweis von Salmonellen
    download file  | open PDF

Contact, forms

National Reference Centre for Salmonella

Beethovenstraße 6
8010 Graz

Dr. Christian Kornschober
Telephone: +43 50 555-61201
christian.kornschober@ages.at

Downloads

    Reptilienfolder (341 K)
    Reptilien als Quelle von Salmonelleninfektionen
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    Nationale Referenzzentrale für Salmonellen - Jahresbericht 2018 (253 K)
    download file  | open PDF

    Salmonellen Jahresbericht 2017 (1.00 M)
    Bericht der Nationalen Referenzzentrale für Salmonellen
    download file  | open PDF

    Salmonellen Jahresbericht 2016 (716 K)
    Bericht der Nationalen Referenzzentrale für Salmonellen
    download file  | open PDF

    Leitlinie personenbezogene Kontrollmaßnahmen bei lebensmittelbedingten Krankheiten (2.07 M)
    Teil1: Salmonellose (Salmonella non-typhi), Campylobacteriose
    download file  | open PDF

    Salmonellenbekämpfung 2016 (0.92 M)
    Ergebnisse des Salmonella-Bekämpfungsprogramms 2016
    download file  | open PDF

    Empfehlungen Futtermittel (663 K)
    Empfehlungen zur Beherrschung von Salmonellen in der Futtermittelproduktion
    download file  | open PDF

    Heimtierfutterherstellung_pdf (145 K)
    Infoblatt zur Heimtierfutterherstellung
    download file  | open PDF

    Zusammenfassung SINS Studie (47 K)
    Staub als Indikator zum Nachweis von Salmonellen
    download file  | open PDF

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