# Current Challenges in _Yersinia_ Diagnosis and Treatment
## 4 Epidemiology of _Yersinia_ Infection  
The infections of _Yersinia_ spp. have been reported from all continents but are most common in Europe [31]. In developed countries, _Y. enterocolitica_ is a frequent cause of gastroenteritis. Interestingly, it is also the third most common bacterial cause of gastrointestinal infections in European populations [32].  
The prevalence of yersiniosis is higher in northeastern Europe than in other European countries [33]. For example, the incidence rate of _Y. enterocolitica_ in Sweden is 2.27-6.18 cases per 100,000 inhabitants [34]. Yersiniosis is also reported in Poland [35] and a decreasing trend in the incidence of yersiniosis has been observed since 2009. In 2018-2020, a total of 542 cases of yersiniosis were recorded (456 intestinal and 86 extraintestinal). In 2020, a sharp decrease in the number of yersiniosis infections was observed compared to previous years, resulting from the introduction of many restrictions to reduce the spread of the SARS-CoV-2 virus, which also affected the number of yersiniosis infections [36]. In the USA, _Y. enterocolitica_ causes about 116,716 human infections annually [37]. The Centers for Disease Control and Prevention in the USA assessed that _Y. enterocolitica_ is responsible for 640 hospitalizations and 35 deaths yearly [38]. The incidence of yersiniosis is also monitored in developing countries; however, the exact prevalence of infections is unknown in Africa and the Middle East due to insufficient diagnostics [39].  
The decreasing EU trend for confirmed yersiniosis cases since 2008 stabilized during 2013-2017. In 2017, yersiniosis was the third most reported zoonosis in the European Union (n = 6823 confirmed cases reported by twenty-six MS (member states); the notification rate was 1.77 cases per 100,000 population, which was 2.8% lower than in 2016). The highest country-specific notification rates were in northeastern Europe. The decreasing trend of human yersiniosis was observed in the EU/EEA from 2008 to 2017, but the trend did not show any significant increase or decrease in the past five years (2013-2017). The most common bioserotype was 4/O:3, followed by 2/O:9 and three fatal cases were reported among the 4467 confirmed yersiniosis cases for which this information was available. Of the 12 identified outbreaks, 11 were caused by _Y. enterocolitica_ (the large outbreak consisted of 80 patients in Denmark) [40].  
Currently, in the European Union, yersiniosis is the third most common foodborne zoonosis in humans (7919 confirmed cases of yersiniosis in humans in 2022 and 8738 in 2023). According to the European Food Safety Authority (EFSA) and the European Centre for Disease Prevention and Control (ECDC, 2024), a stable trend in incidence was observed between 2018 and 2023. Most cases of yersiniosis are caused by _Y. enterocolitica_, although sporadic outbreaks caused by _Y. pseudotuberculosisis_ occur. For example, in 2022, _Yersinia enterocolitica_ was the species reported in the majority (98.7%) of human cases, while _Y. pseudotuberculosisis_ was reported in only 1.3% of human cases [41]. The _Y. pseudotuberculosisis_ infection is rare, and usually, sporadic cases are reported. Nevertheless, outbreaks have been reported in Japan [42], Canada [43], Europe [6], Russia [3], and New Zealand [4]. In Europe, the disease is usually a self-limiting acute enteritis that spreads to the mesenteric lymph nodes [14; 44; 45]. However, outbreaks of _Y. pseudotuberculosisis_ infections can be severe and are characterized by systemic inflammatory symptoms called Far Eastern scarlet fever (FESLF), mainly reported in Russia and Japan [46]. FESLF is a rare, severe inflammatory disease that, unfortunately, is often lethal [46]. FESFL, also known as Izumi fever, has clinical features resembling those of Kawasaki disease and mainly develops among young children, adolescents, and young adults in Japan. The incidence of this disease has markedly decreased because of improved sanitation [47].