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.
A total of 28 foodborne illness outbreaks were reported in 2022, eight more than in 2021. In total, 128 people were affected by the outbreaks, slightly more than in 2021 (92 people) and 2020 (67 people) but significantly fewer than in 2019 (793 people). Fifty-seven persons required hospitalization in connection with the outbreaks (2021: 27, 2020: 17, 2019: 159); there were four deaths (2021: 2 deaths, 2020: no deaths, 2019: one death). The average number of persons per outbreak was 4.6 and affected between two and 30 persons in each outbreak. For the first time, the number of general outbreaks was higher (n = 14) than household outbreaks, and there were also four outbreaks with unknown status.
Salmonella emerged as the most common outbreak agent (11 outbreaks, 80 affected persons). Campylobacter was second (8 outbreaks, 17 cases), followed by five outbreaks due to Listeria monocytogenes (17 persons, all hospitalized, 4 deaths), two outbreaks due to norovirus (10 persons), and one each due to STEC and Shigella sonnei (2 cases each).
A major foodborne outbreak in Europe in 2022 was caused by the monophasic variant of S. Typhimurium ST34, with 14 persons falling ill in Austria and 5 requiring hospitalization. Across Europe, a total of 324 people were affected. The contaminated food was chocolate from a Belgian factory. Production on site was stopped and a worldwide product recall was issued.
In the listeriosis outbreak caused by L. monocytogenes Sg IVb/ST1/CT6568, five people were affected, two of whom died. The outbreak started back in 2020 with three people (1 death), and 2 people were affected in 2021 (1 death). The infections were caused by consumption of contaminated dairy products of various types. An Austria-wide product recall was issued, and production at the milk processing plant was halted.
One outbreak with strong evidence - caused by L. monocytogenes Sg IIb/ST517/CT3971 - affected three people, all of whom required hospitalization. The food responsible was contaminated pork jausen bacon.
The largest outbreak with weak evidence was caused by Salmonella Typhimurium ST 19 and affected 30 persons in Austria. Ten of them had to be hospitalized; the contaminated food was chocolate.
Two outbreaks were acquired abroad, one by Campylobacter after a stay in Ecuador and once Shigella sonnei after a stay in India.
|- thereof due to salmonella||452||305||223||208||98||100||53||44||47||34||37||31||21||17||7||9||11|
|- thereof due to Campylobacter||137||108||118||120||82||116||61||58||40||32||40||24||24||22||10||6||8|
|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||128|
|- cases per 100,000 inhabitants in connection with outbreaks||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||1,4|
|- thereof treated in hospital||493||286||338||223||155||179||97||108||121||86||68||56||58||159||17||27||57|
|- Number of deaths||3||1||0||6||2||0||0||0||1||0||0||2||0||1||0||2||4|
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 individuals from multiple households are affected, this is counted as a general outbreak. Household outbreaks account for the majority (approximately 75%) each year because it is often not possible to epidemiologically link cases of illness from different household outbreaks by identifying a single causative food.
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.
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: 17.08.2023