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 2023, 192 initial Yersinia spp. isolates were sent to the National Reference Centre for Yersinia. Of the 192 human isolates, 100 were pathogenic and 92 were apathogenic. Of the pathogenic isolates, 98 strains were identified as Y. enterocolitica. In the remaining two cases, Y. pseudotuberculosis was detected. The incidence of Yersiniosis confirmed by culture by the reference centre was 1.09 per 100,000 inhabitants in 2023. 100 cases were reported to the Epidemiological Reporting System (EMS) (as at 30.01.2024).

Yersinia are facultatively anaerobic (i.e. growing even in the absence of oxygen), pleomorphic, Gram-negative (stained red in the so-called Gram stain) rods that belong to the Enterobacteriaceae family. As psychrophilic (= cold-loving) germs, they can be grown at temperatures between 4°C and 42°C. They are commonly found in temperate climates.

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

In 2022, typing of 105 Y. enterocolitica isolates at the National Reference Center for Yersiniosis revealed 88 isolates bioserovar 4/O:3 (84%) and 17 bioserovar 2/O:9 (16%). In recent years, the incidence of the disease shows the highest incidence in the age groups up to 14 years. In 2022, two cases have been imported, one each from Cuba and Spain. Both imported isolates were Y. enterocolitica serovar O:3, biovar 4.

Diagnostics

A purely symptomatic diagnosis is very difficult on the basis of the clinical picture alone. The cultivation of germs from stool 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 still be excreted in the stool for weeks after the clinical symptoms have subsided. Molecular biological methods such as PCR tests are also available for pathogen detection.

Symptomatology

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

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

In school-age children and adolescents, the infections usually present as acute mesenteric lymphadenitis (inflammatory swelling of abdominal lymph nodes) with abdominal pain. The clinical picture may resemble appendicitis ("pseudoappendicitis").

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

Yersiniosis may be associated with concomitant or secondary symptoms: reactive arthritis, erythema nodosum (= acute inflammation of the subcutaneous fat tissue), arthralgia (= joint pain) or myalgia (= muscle pain). Y. enterocolitica is more likely to lead to gastroenteritis, Y. pseudotuberculosis more often to pseudoappendicitis.