Foodborne disease outbreaks

Consumers expect hygienically safe food and the food industry attaches great importance to the quality of its products. If people nevertheless fall ill as a result of eating food contaminated with pathogens, an attempt should be made to find out the causes.

In individual cases, it is usually not possible to find the cause of the disease in the variety of foods consumed. However, in group illnesses, known as foodborne outbreaks, there is a better chance of finding the food that served as the transmission vehicle for the pathogen by working out characteristic similarities between cases.

Definition: a foodborne outbreak is defined in the Zoonoses Act 2005 as follows: The occurrence, under given circumstances, of a disease and/or infection associated or likely to be associated with the same food or food business in at least two cases in humans, or a situation in which the cases detected are more prevalent than expected.

Situation 2021

In 2021, a total of 20 foodborne illness outbreaks were reported, one fewer than in 2020. In total, 92 people were affected by the outbreaks, slightly more than in 2020 (67 people) but significantly fewer than in 2019 (793 people). Twenty-seven people required hospitalization in connection with the outbreaks (2020: 17, 2019: 159), and there were two deaths (2020: no deaths, 2019: one death). Five outbreaks were general outbreaks as opposed to 15 household outbreaks. Salmonella emerged as the most common outbreak agent (nine outbreaks, 61 affected). Campylobacter was second (six outbreaks, 12 cases), followed by four outbreaks due to STEC (14 cases) and one due to Listeria monocytogenes (five persons sickened, two deaths).

The largest foodborne outbreak in Austria in 2021 was caused by the monophasic variant of S. Typhimurium (MLVA profile 3-10-7-18-0311), sickening 31 persons and requiring hospitalization of ten. A link could be established to various dishes served at a restaurant and the animals in the adjacent petting zoo. One outbreak was part of an international outbreak with 348 cases of illness caused by S. Braenderup in association with consumption of imported Galia melons from Honduras. In Austria, 11 people were affected, seven of whom had to be hospitalized.

In the listeriosis outbreak caused by L. monocytogenes IIa ST511 CT4383, five persons became infected during consumption of meat products from a slaughterhouse, two of whom died. One outbreak involving two persons was caused by Campylobacter jejuni. The contaminated food was uncooked chicken meat originating in the European Union. Three outbreaks were foreign-acquired, two by S. Enteritidis, one after stay in Romania and once unknown, and one by STEC (stay Turkey).

Year 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
Foodborne outbreaks 609 438 368 351 193 232 122 133 96 78 80 69 52 48 21 20
- thereof due to salmonella 452 305 223 208 98 100 53 44 47 34 37 31 21 17 7 9
- thereof due to Campylobacter 137 108 118 120 82 116 61 58 40 32 40 24 24 22 10 6
Number of people sickened (in connection with foodborne outbreaks) 2.530 1.715 1.376 1.330 838 789 561 568 790 333 436 227 222 793 67 92
- Persons ill in connection with outbreaks per 100,000 inhabitants 30,7 20,7 16,5 15,9 10,0 9,4 6,7 6,7 9,3 3,9 5,0 2,6 2,5 9,0 0,7 1,0
- thereof treated in hospital 493 286 338 223 155 179 97 108 121 86 68 56 58 159 17 27
- Number of deaths 3 1 0 6 2 0 0 0 1 0 0 2 0 1 0 2


Types outbreaks

Based on the Austrian Zoonoses Act, we collect outbreak data annually and forward it to the EU. Certain classifications result for this reporting: Outbreaks in which only members of a single household are affected are categorized as a household outbreak. If people from multiple households are affected, it is counted as a general outbreak. Household outbreaks account for the majority each year because it is often not possible to link cases of illness from different household outbreaks epidemiologically by identifying a single causative food. In 2021, 75 % of all outbreaks were classified as household outbreaks.

Outbreak clarification

The aim of the outbreak survey is not only to stop the outbreak that is currently taking place, but above all to prevent such diseases in general in the future.

Detailed and systematic searches can succeed in locating both the infectious vehicle, that is, the food that transmitted the infectious agent to humans, and the reservoir, which is the habitat in which an infectious agent normally lives. Only then is it possible to set targeted and meaningful interventions. These measures should result in the elimination of the outbreak cause, namely the infectious agent, from the food chain and consumers are no longer exposed to this agent.

The following historical example illustrates the preventive medical potential of an outbreak investigation: In July 2004, it was possible to clarify a foodborne outbreak caused by Salmonella Enteritidis phage type 36, a very rare Salmonella type in Austria, which affected 38 people in four provinces, and trace it back to a flock of laying hens. The flock was eradicated, the farm thoroughly cleaned and disinfected; subsequently, new laying hens were housed. As a result of these measures, not a single further case of illness caused by Salmonella Enteritidis phage type 36 has been reported in Austria since then.

Since 2009, bacterial and viral foodborne infections and poisonings have been reported via the EMS, an area-wide surveillance system. However, these reporting figures must be viewed in a nuanced manner: Numerous factors can lead to an underestimation of the actual illness figures ("underdetection/underreporting"). Depending on the pathogen, the data situation often varies: for salmonella, for example, data are available from Europe-wide baseline studies, surveillance and control programs. The decrease in salmonellosis cases is an effect of measures implemented on the basis of these data. Toxoplasmosis, on the other hand, is not reportable, although new scientific evidence suggests a link with food. All of these factors must be considered when assessing the true public health significance of a disease.


In accordance with the provisions of the Epidemic Diseases Act, the locally competent district administrative authorities must, through the public health officers at their disposal, immediately initiate the surveys and investigations required to identify the disease and the source of infection in the event of any report or suspicion of the occurrence of a notifiable disease - and thus also in the case of foodborne outbreaks. In addition, the Zoonoses Act 2005 obliges the respective competent authorities to investigate foodborne disease outbreaks and, as far as possible, to conduct appropriate epidemiological and microbiological investigations in the process.

In doing so, the authorities have the option to call in experts. Simply stepping up untargeted food sampling has repeatedly proven to be ineffective in the past. In many outbreaks, the causal food (or the affected contaminated batch of the causal product) is no longer available for microbiological investigations at the time of the surveys.

In these cases, an epidemiological study can provide insights that enable preventive measures to be taken to avoid similar incidents in the future. The lessons learned from successfully cleared national and international outbreaks in recent years have put the necessity and usefulness of epidemiological clarifications beyond question.

Theme Report

Many authorities and institutions from different disciplines are involved in the monitoring of the food chain. Due to the complexity and the partly different objectives, a comprehensive, joint consideration is absolutely necessary. The 4th report in the AGES Wissen Aktuell series, "Foodborne Infectious Diseases", provides this overview. It also describes the causes that can lead to contamination of animal foodstuffs with certain pathogens and the measures that can be taken to reduce them by both producers and consumers.

In Austria, around 8,000 foodborne illnesses are recorded in the national epidemiological reporting system (EMS) every year. According to the WHO definition, foodborne infectious diseases are "diseases of an infectious or toxic nature that are actually or probably attributable to the consumption of food or water." In total, more than 250 pathogens and toxins are known to cause such diseases. This report is limited to 20 pathogens that are of concern in Austria (Campylobacter, Clostridium difficile, EHEC/VTEC, Listeria, Salmonella, Shigella, Vibriones, Yersinia, Noroviruses, rotaviruses, sapoviruses, hepatitis viruses, Cryptosporidium parvum, Toxoplasma gondii, Cyclospora cayetanensis, Giardia and the toxin producers Staphyloccus aureus, Bacillus cereus, Clostridium botulinum, Clostridium perfringens). Pathogens that are virtually absent in Austria or only occur as travel diseases were not taken into account.

Last updated: 10.10.2022

automatically translated