Yersinia enterocolitica, a gram-negative coccobacillus, is a zoonotic infection in wild and domestic animals, which, when transmitted to humans, can cause yersiniosis. Acute yersiniosis commonly presents in children and adolescents as acute, self-limiting bloody diarrhea that can last 1 to 3 weeks. Children younger than 5 years are at higher risk for contracting the disease and developing complications such as mesenteric lymphadenitis and extraintestinal infections.Y enterocolitica is often transmitted via the fecal-oral route, and infection is typically acquired by eating contaminated pork, unpasteurized milk, and, as has been reported in some cases, from vegetables and contaminated water supplies. The most commonly reported source is raw pork products such as tripe or intestines (chitterlings). Transmission has also been observed with close interaction with animals—pets, petting zoos, and families working on farms. Outbreaks of yersiniosis are common in child care centers and have been found to have a seasonal pattern, most frequently occurring during winter. It has been found to be most common in developed countries in the temperate zones, including the United States, the Netherlands, Belgium, France, Canada, and Australia.The incubation period for yersiniosis ranges from 1 to 2 weeks and is normally within 4 to 6 days, making it a subacute cause of gastrointestinal illness. Y enterocolitica causes disease by directly invading the mucosa of the terminal ileum and migrating in the mesenteric and ileocecal lymph nodes. This can cause mucosal ulceration of the terminal ileum, necrotic lesions in Peyer patches, and inflammation and enlargement of lymph nodes. Pharyngitis has been observed in some children, and Yersinia has been isolated from tonsillar cultures. The disease is self-limiting in most cases; however, stool shedding can persist for up to 40 days after diarrheal symptoms have resolved.The annual incidence of the disease has been variable due to differences in testing patterns. In northern America it ranges from 0.14 to 0.19 per 100,000, and in Europe it ranges from 0.1 to 7.4 per 100,000. There is an increased prevalence of the infection in immunocompromised patients. Yersinia enterocolitica infections are considered rare, but there has been a notable increase in incidence during the past decade due to the development of nucleic acid amplification test/polymerase chain reaction (NAAT/PCR) testing, resulting in enhanced identification. Increasing incidence of yersiniosis in countries that have started to include PCR testing for Y enterocolitica in patients with gastroenteritis shows that this is an underreported pathogenic cause of pediatric bloody diarrhea. Testing for Yersinia using the NAAT/PCR test should be strongly considered in immunocompromised patients with diarrhea.Historically, pathogen detection is via stool cultures, which will be positive during the first 2 weeks of the infection. Identification requires a special culture, and testing for Yersinia has been reserved only for when there is increased clinical suspicion. Some centers show that clinicians might need to take a more careful history to identify patients with exposure to potential sources, other people with bloody diarrhea, and participation in child care centers. For example, a hospital in the United Kingdom included routine NAAT/PCR testing for Y enterocolitica in their panel of tests for patients presenting with gastroenteritis and found an incidence of 13.8 per 100,000 versus 0.1 per 100,000 (before NAAT/PCR testing over a 30-month period). In the United States, the introduction of NAAT/PCR testing in patients with cancer with gastrointestinal disease in a center revealed increased incidence from 0.016 to 0.13 per 1,000 admissions in an 8-year period.Children younger than 5 years will usually present with abdominal pain, fever, and bloody diarrhea. Routine stool microscopic examination will show mucus, leukocytes, and red blood cells. Older children and adolescents can present with a pseudo-appendicitis syndrome, with abdominal pain, nonbloody diarrhea, fever, and right lower quadrant tenderness. Blood work, including cultures, are frequently unremarkable. It is clinically difficult to differentiate from bacterial dysentery caused by other pathogens. Vigilance in identifying those who are at risk is essential. Clinical clues such as prolonged and more elevated fevers and lymph node involvement can help distinguish from other more common causes of bloody diarrhea in the pediatric patient. A high clinical suspicion should prompt NAAT/PCR testing for Yersinia, particularly in immunocompromised patients.Extraintestinal manifestations with this pathogen include suppurative lymphadenitis, meningitis, osteomyelitis, lung abscess, carditis, and mycotic aneurysms. Focal infections in the form of liver or spleen abscesses have been reported in patients with increased iron storage (eg, sickle cell disease, β-thalassemia, and deferoxamine use). Postinfectious sequelae of Y enterocolitica include proliferative glomerulonephritis, erythema nodosum, and arthritic syndromes, which are more common in patients with human leukocyte antigen (HLA)–B27. Younger patients who get yersiniosis are more likely to develop reactive arthritis, and older children and adolescents are more likely to develop Reiter syndrome (urethritis, conjunctivitis, iritis).Hydration and supportive care remain mainstay treatments in the management of yersiniosis. Treatment with antibiotics is indicated in patients who are immunocompromised and those who develop septicemia or have focal infections. Y enterocolitica is sensitive to trimethoprim-sulfamethoxazole (TMP-SMX), third-generation cephalosporins, aminoglycosides, and doxycycline. TMP-SMX (TMP, 8 mg/kg per day; SMX, 40 mg/kg per day, in 2 divided doses) is used as empirical therapy in most patients, with cefotaxime and ceftriaxone as alternatives. There is no evidence that antibiotics can shorten the clinical course in patients with uncomplicated enteritis or mesenteric adenitis. Resistance has been reported with amoxicillin, ampicillin, amoxicillin-clavulanate, all first-generation cephalosporins, and fluoroquinolones.Vaccination is being investigated for immunization of humans and animal reservoirs of Yersinia species. Earlier vaccine development for Yersinia suggested that killed-type immunization can be effective and will have a better safety profile. However, studies of oral vaccination against Yersinia species using live attenuated Yersinia pseudotuberculosis have been found to effectively induce both humoral and cell-mediated immune responses. The Yersinia species share 73% genetic identity, including a virulence plasmid that encodes a type three secretion system, allowing for cross-protection from plague and yersiniosis. Currently, vaccines under investigation still require more studies in other animal models and nonhuman primates.Y enterocolitica might be not as uncommon as we think. It is an important pathogen to identify in children with bloody diarrhea, and older children can present with nonbloody diarrhea. Because this pathogen is not routinely tested for, a careful history is critical to identify patients at risk, and health-care providers need to know when to ask for special stool cultures to be performed. Eliciting information about undercooked pork in chitterlings, ingestion of unpasteurized milk, pig exposures in petting zoos or farms or as pets, and exposure to others with bloody diarrhea is imperative in getting a comprehensive history. The recent development of PCR testing for Yersinia might be an important improvement in enhancing identification. Minimizing transmission in child care centers has been a critical area on which to focus because young children might not be toilet trained and often have more hand-to-hand transmission without careful handwashing. The development of a vaccine seems promising for public health control.