Yersiniosis is a foodborne infectious disease caused primarily by bacteria of the species Yersinia (Y.) enterocolitica and, less commonly, Y. pseudotuberculosis.

Enteric yersiniosis occurs worldwide and is the third most common bacterial zoonosis in the EU. Y. enterocolitica is prevalent in the environment and in the animal population, primarily in pigs, less frequently in dairy cows. Y. enterocolitica can also be found in wild animals. Y. pseudotuberculosis can be found primarily in the environment. Similar to Listeria, Y. enterocolitica can also multiply on contaminated food in the refrigerator.

animals, mainly pigs and to a lesser extent dairy cows

Yersiniosis is usually caused faecal-orally by consumption of contaminated food and water, especially raw or medium-cooked pork and raw or inappropriately heated dairy products. The bacteria can also multiply at 4 °C (e.g. refrigerator). In major foodborne Y. pseudotuberculosis outbreaks in the EU, contaminated vegetables (bean sprouts, tofu), water and milk have been confirmed as vehicles of infection. Transmission can also occur through contaminated blood supplies. Direct transmission from infectious animals and humans is rare.

3 to 7 days

In children, the disease usually manifests itself with gastrointestinal symptoms, whereas adults may show signs of appendicitis (pseudo-appendicitis). The classic symptoms are diarrhea, fever, and severe abdominal pain (untreated for a duration of 1-3 weeks). The diarrhea may be watery but also bloody; after a few days, joint pain, joint inflammation and skin changes may also occur. In rare cases, the so-called Reiter syndrome (arthritis, urethritis, conjunctivitis) may develop.

In pigs, which are considered to be the main reservoir for Y. enterocolitica, bloody diarrhoea may occur in individual cases, and joint and lung inflammation can be found in young animals. In most cases, however, infections remain asymptomatic and unnoticed by the animal owner.

Infections with Yersinia are usually self-limiting, therefore symptomatic treatments to maintain water and electrolyte balance are sufficient. Severe courses justify the use of antibiotic therapy.

Hygiene during slaughter of pigs; avoidance of raw pork and raw pork products and raw milk

In 2024, 225 initial Yersinia spp. isolates were sent to the National Reference Centre for Yersinia. Of these, 98 isolates proved to be pathogenic, of which 96 were identified as Y. enterocolitica and the remaining two as Y. pseudotuberculosis. The incidence of Yersiniosis confirmed by culture by the reference centre was 1.1 per 100,000 inhabitants in 2024. 90 cases were reported to the Epidemiological Reporting System (EMS) (as at 31.01.2025).

Yersiniae are facultatively anaerobic (i.e. they grow even in the absence of oxygen), pleomorphic, Gram-negative (coloured red in the so-called Gram stain) rods that belong to the Enterobacteriaceae family. As psychrophilic (= cold-loving) germs, they can be cultivated at temperatures between 4 °C and 42 °C. They are often found in temperate climates. They are frequently found in temperate climate zones.

The genus Yersinia includes 14 species, with enteropathogenic Yersinia(Y. enterocolitica and Y. pseudotuberculosis) being obligate pathogens of human medical importance.

In 2024, typing of the 96 Y. enterocolitica isolates in the national reference centre for yersiniosis revealed 77 x bioserovar 4/O:3 (80 %),18 x bioserovar 2/O:9 (19 %) and once bioserovar 3/O:3 (1 %). In recent years, the disease has occurred most frequently in the age group 0 to 14 years.

Diagnosis

A purely symptomatic diagnosis based on the clinical picture alone is very difficult. Stool culture is the method of choice, also to determine serotypes and biotypes. Blood, cerebrospinal fluid, punctates, lymph node aspirate or peritoneal fluid can also be used. In untreated patients, the germs can be excreted in the faeces for weeks even after the clinical symptoms have ceased. Molecular biological methods such as PCR tests are also available for pathogen detection.

Symptoms

The infections caused - so-called yersiniosis - show a broad spectrum of symptoms.

In infants and young children, self-limiting, acute gastroenteritis usually occurs with vomiting, watery to bloody diarrhoea and fever. The illness can last one to two weeks.

In schoolchildren and adolescents, the infections usually take the form of acute mesenteric lymphadenitis (inflammatory swelling of abdominal lymph nodes) with abdominal pain. The clinical picture can resemble appendicitis (= inflammation of the appendix) ("pseudoappendicitis").

Different clinical forms occur in adults, such as flu-like infections with pharyngitis (= pharyngitis), myalgia (= muscle pain) and fever, or ileocolitis (= inflammation of the large intestine and parts of the small intestine) with involvement of the mesenteric lymph nodes ("pseudocrohn's disease").

Yersiniosis can be associated with concomitant or secondary symptoms: reactive arthritis, erythema nodosum (= acute inflammation of the subcutaneous fatty tissue), arthralgia (= joint pain) or myalgia (= muscle pain). Y. enterocolitica tends to lead to a gastroenteritis clinical picture, Y. pseudotuberculosis more frequently to pseudoappendicitis.