Salmonella is the second most common diarrheal pathogen in Austria and is mainly transmitted through food. Infection occurs through ingestion of food containing salmonella, primarily eggs and egg products, poultry, meat and dairy products, and ice cream (however, there is hardly any food in which salmonella has not been detected). Illness usually only occurs when relatively large amounts of bacteria (more than 100,000 germs) are ingested. This number of germs, known as the infectious dose, is easily reached if food is not stored properly, since Salmonella can multiply explosively in food at room temperature within a few hours (doubling the number of germs every 20 minutes). However, the infection dose may be significantly lower in infants, the elderly, persons with a compromised immune system or also in connection with fatty foods (e.g. chocolate).

Salmonellosis is a diarrheal disease (including vomiting and abdominal cramps) that is common worldwide and is caused by infection with bacteria of the genus Salmonella(S.). Throughout Europe, the two serovars S. Enteritidis and S. Typhimurium are the main causative agents of foodborne salmonellosis in humans. The pathogens of typhoid and paratyphoid fever(S. Typhi and S. Paratyphi) are to be distinguished from them: These do not occur in Austria, but only in tropical and subtropical countries with low hygiene standards; they cause systemic diseases with intestinal involvement.

The transmission routes of Salmonella are very diverse. Farm animals can become infected via Salmonella-contaminated feed. In chickens, Salmonella colonization often remains hidden because the animals do not become ill from it. Occasionally, entire flocks of laying hens become unrecognized permanent excretors. Transfer of the germs to the still unlaid egg in the hen leads to eggs containing Salmonella. If these are not sufficiently heated before consumption, they can pose a health risk to humans.

Salmonella generally grows in a temperature range of 10 to 47 °C and is not killed by freezing. Heating to above 70 °C is considered to kill germs. However, since this temperature must be reached throughout the food during cooking, a cooking time of 15 minutes above 70 °C should be observed.

Domestic and farm animals (especially poultry), wild animals (birds) and exotic reptiles

Salmonella is mainly transmitted by eating 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, may also be contaminated with Salmonella.

Unheated or insufficiently heated meat (such as poultry meat, kebabs, minced meat, raw sausages) can pose a risk during processing if they come into contact with products that are no longer heated (e.g. potato salad). This transmission to other foodstuffs (cross-contamination) can also occur through insufficiently cleaned utensils, such as cutting boards, knives and towels or failure to wash hands. In addition to kitchen hygiene, great attention must be paid to the continuous refrigeration of raw products during food preparation.

A small proportion of salmonelloses occur through smear infections, an 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 considered as reservoirs for such smear infections. Thorough cleaning of the hands with soap and warm water is recommended after each animal contact.

6-72 hours, usually 12-36 hours

Symptoms of the disease may include nausea, diarrhea, fever, vomiting, circulatory problems and abdominal cramps. The symptoms usually last only a few days. The course of the disease is often mild or asymptomatic, depending on the number of germs ingested and the immune status of the affected person. In elderly persons, salmonellosis can quickly lead to a life-threatening condition due to the high fluid loss and the associated circulatory stress.

Patients with gastrointestinal complaints without other risk factors should only be treated with antibiotics in special cases, as this can prolong bacterial excretion and develop resistance to antibiotics. In most cases, a therapy that balances the water and electrolyte balance is sufficient.

Food, especially meat, poultry, eggs or pasta with cream filling, should be well boiled and not kept at room temperature for several hours when cooked. After handling raw poultry meat, thorough hand washing is essential before starting other kitchen tasks. Defrosting water from frozen meat should be emptied into the sink and then rinsed hot. All work surfaces and utensils that have been in contact with raw poultry meat, other raw meat or raw eggs should be cleaned with detergent and hot water. Allow freshly prepared food to cool and then store in the refrigerator unless it is to be eaten immediately.

People with salmonellosis must not handle food professionally during the period of illness.

In 2023, 1,278 laboratory-confirmed cases of the disease were reported to the epidemiological reporting system (EMS) (EMS, as at 28/02/2024), which corresponds to an incidence of 14 cases per 100,000 inhabitants. Initial isolates from 1,218 sick/infected persons were sent to the NRZ Salmonella. Salmonella was therefore once again - behind Campylobacter - the second most frequently reported cause of bacterial food poisoning in Austria.

From 2002 to 2016, the number of salmonellosis cases fell by 83% (2002: 8,405 initial isolates; annual report of the Salmonella Centre 2002). This decline in salmonellosis in humans was almost exclusively due to the decline in S. Enteritidis infections(2002: 7,459 isolates; 2016: 671 isolates). The increase in salmonellosis in 2019 compared to 2018 can be attributed to an Austria-wide outbreak caused by S. Enteritidis. The infections mainly occurred in Asian restaurants through the use of eggs containing salmonella. In 2020 and 2021, due to the SARS-CoV-2 pandemic and the associated measures, the number of stool samples sent in and the resulting isolation of salmonella fell massively.

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

In 2023, 5,400 food samples were analysed for salmonella, mainly meat and meat preparations (approx. 1,300 samples), other and ready-to-eat foods (approx. 1,350 samples), milk, dairy products (approx. 670 samples), fruit, fruit juices, vegetables, salads, spices and mushrooms (approx. 450 samples), baked goods (approx. 300 samples), eggs and egg products (approx. 200 samples), fish and fish products (approx. 210 samples). Salmonella was detected in 62 samples, predominantly in meat and meat preparations from poultry (51 samples). S. Infantis was isolated most frequently (43 times), 28 of which were in fresh chicken meat and chicken meat products. S . Enteritidis was found in a bakery product, S. Typhimurium (monophasic) in a sample of poultry meat (without further specification of the poultry).

For humans, animal foods are the most important source of Salmonella infection. In order to determine the importance of different animal populations as reservoirs of Salmonella, uniform EU-wide baseline studies have been carried out in various farm animal species in recent years. These studies proved for Austria that poultry (laying hens, broilers and fattening turkeys) play the most important role for Salmonella illnesses 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 the serovars S. Enteritidis and S. Typhimurium, including its monophasic variant, which are most important in human medicine: This is 2% for laying hens, 1% for broilers and turkeys, and 1% for parent stock of chickens (in addition to S. Enteritidis and S. Typhimurium, S. Infantis, S. Virchow, and S. Hadar also fall within the target here). In 2022, the specified targets were achieved in Austria for all directions of poultry use.

S. Infantis represents an increasingly frequently detected serovar: since 2016 as the third most important serovar in human diseases, in 2022 as the fourth most important serovar and as the most frequent serovar in poultry meat and broiler flocks. This S. Infantis is mostly a multidrug-resistant variant that shows resistance to the three classes of antibiotics: quinolones, sulfonamides, and tetracyclines.

The Salmonella control program in the EU requires that the most significant Salmonella serovars for humans be controlled in animal populations. Since S. Infantis is not included among the serovars to be controlled in broiler chickens, no financial support is provided for control procedures, such as possible vaccination or culling of flocks, throughout the EU. 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 slaughterhouse operators refuse to slaughter Salmonella-positive herds at all. As a result, broiler herds are not slaughtered but culled. This S. Infantis strain has become established in domestic 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 3% since the control program began in 2010.

Animal feed is subject to a permanent monitoring programme in Austria. As part of the official controls, samples are taken both on farms and in warehouses, compound feed plants and trading companies. Both complete feed mixtures and individual components are officially analysed. In 2023, salmonella was detected in two of 212 analysed feed samples for livestock (0.9%) (once S. Brandenburg and once S. Rissen). Protein-rich extraction meals or cakes (by-products from the edible oil processing industry) are considered to be the most significant source of salmonella. These can introduce salmonella into the feed chain and contaminate the compound feed produced from them.

In 2023, 54 pet food and chew toy samples were officially analysed. Six different serovars were detected in four of these (7.4%), with three different serovars identified in one sample and two serovars each in two others: S. Infantis and S. Derby were identified twice in total and S. Anatum, S. Mbandaka, S. Bredeney and S. Typhimurium, monophasic, were identified once each. Handling pet food, especially chew toys, poses a demonstrable risk to humans. You should therefore wash your hands after feeding and playing with dogs or cats.

If Salmonella are isolated from human medical or animal test material or from foodstuffs, laboratories in Austria are obliged to send these isolates to the National Reference Center for Salmonella (NRZ S) in accordance with the Epidemic Act, the Poultry Hygiene Ordinance and the Food Safety and Consumer Protection Act. There, typing of the isolates is performed to elucidate possible links between the occurrence of the pathogens along the food chain.

In 2021, 1,048 initial human isolates were typed at the National Reference Center for Salmonella. The discrepancy in the number of reported cases to first isolates is due in part to the reference center's practice of counting multiple infections separately (e.g., detection of S. Enteritidis and S. Typhimurium in one submission are counted as two events/first isolates). In addition, isolates from persons infected with Salmonella but not ill, as well as from persons who did not become infected with Salmonella via food but, for example, through contact with reptiles, are also recorded.

The pathogen is usually detected by culturing from stool (feces), possibly also from blood or pus. Examination of blood for specific antibodies is not conclusive.

The National Reference Center for Salmonella at the AGES in Graz performs serotyping according to the White-Kauffmann-Le Minor scheme for all human and non-human salmonellae detected in Austria. In addition, the most important serotypes for human medicine, S. Enteritidis and S. Typhimurium, are further differentiated using MLVA (Multi Locus Variable Number Tandem Repeats Analysis). For isolates suspected of being part of a (food-borne) outbreak, typing by means of sequencing (NGS, next generation sequencing) is performed.

Salmonella infections can be detected in almost all animal species. Reptiles are particularly affected by latent infections with a broad spectrum of serovars. Salmonellosis in cattle: S. Dublin is adapted to cattle, but other serovars can also cause general infections with severe clinical pictures. Calves from the 2nd week of life are most susceptible. The predominant symptoms are diarrhoea, disturbances of the general condition or pneumonia, which become milder with increasing age. In cows, however, severe diseases with diarrhoea, milk loss and abortions may occur. Salmonellosis in pigs: Adapted species are S. Choleraesuis and S. Typhisuis. Non-adapted serovars cause disease much less frequently, especially with diarrhea. Affected are weanling pigs and young pigs up to 60 kg, the infection usually progresses as a febrile general disease with pulmonary symptoms, more rarely with diarrhoea. Abortions are possible in sows. Salmonellosis in sheep: S. Abortusovis is strictly adapted to sheep and is one of the most important abortive pathogens. Oral or mating infection is followed by a general septicaemic infection. Typical symptom is lambing in the 4th or 5th month of gestation, besides puerperal complications and general diseases of all ages. Non-adapted serovars cause latent infections and diarrhea as well as abortions in sheep. Salmonelloses in horses: S. abortusequi is the adapted type; after oral infection or infection via the mating act, a general infection develops that can lead to foaling in the 4th month of gestation. Life-weak foals are also possible. Mares develop resilient immunity after abortion. Unadapted serovars can lead to asymptomatic disease with shedding of pathogen or mild to severe disease up to septicemia. Salmonellosis in dogs and cats: These species have a higher resistance to Salmonella, there are no adapted serovars. Most often latent infections are observed, under the influence of favoring factors, diarrhea, vomiting and fever may also develop. Salmonellosis in chickens: 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 responsible for white chick dysentery or pullorum disease and causes acute septicemic infections in chicks up to 3 to 6 weeks of age. Biovar gallinarum is the causative agent of so-called chicken typhus, which occurs primarily in older chickens. Infections with non-adapted types usually do not cause disease in the chicken, but latent infections. However, these are an important source of foodborne infections and therefore receive considerable attention. The most important serovar in this context in Austria is S. Enteritidis, followed by S. Typhimurium. Salmonellosis in waterfowl: has received increased attention as a potential source of infection for humans long before chickens, therefore special rules for the consumption of duck eggs have been in place for a long time. Living in standing water, these animals have increased infection pressure. Diseases with diarrhoea and septicaemia occur mainly in young animals (keel disease: back swimming of diseased animals).

Salmonella in dust: Protein-containing straight feedstuffs such as soybean, rapeseed or sunflower extraction meal are considered a significant source of contamination for compound feed and compound feed operations. In this context, Salmonella is present in feeds in uneven distribution and often in very low concentrations. These factors make sampling and analytical detection of positive batches difficult.

However, even if feedstuffs contain very few Salmonella, optimal multiplication conditions, for example in the poultry intestine, can infect the entire livestock within a few days without clinical symptoms appearing in the animals. The infection of a flock is then only manifested by positive boot swab samples.

For routine controls in a compound feed mill, dust samples from the process environment are particularly suitable in addition to the regular incoming inspection of feed materials. Due to their large surface area, dust particles are an ideal medium for pathogens, thus even low levels of Salmonella contamination can be found. Dust, which is drawn along the entire production chain of a feed, is thus a very sensitive matrix for the detection of Salmonella and reflects, as it were, the hygiene status of a compound feed plant.

Decontamination with organic acids: Salmonella in feed can cause enormous economic damage in the affected compound feed plants and farms, and affected feed is therefore not marketable. As a matter of principle, the greatest possible hygiene must be ensured in all work steps at the compound feed plant and, accordingly, the avoidance of contamination or recontamination with Salmonella after thermal treatment of the feed.

Decontamination of Salmonella in feed is permitted by feed law. There are few options available to a compound feed manufacturer for decontamination. With appropriate effort, hygienization of the feed can be achieved primarily by thermal processes. If heat treatment is not possible or not desirable (e.g. in the case of laying meal), the feed can be treated with organic acids.

Hygienization of feed containing Salmonella by means of organic acids is only recommended for the treatment of single feeds due to the high acid additions required. Decontamination of compound feeds is not recommended due to the high acid additions required, for example because of resulting feed refusal or interactions with other feed components.

Recommendations for the control of salmonella in feed production