Name of the Organism:
Yersinia enterocolitica (and Yersinia pseudotuberculosis)

Y. enterocolitica, a small rod-shaped, Gram-negative bacterium, is often isolated from clinical specimens such as wounds, feces, sputum and mesenteric lymph nodes. However, it is not part of the normal human flora. Y. pseudotuberculosis has been isolated from the diseased appendix of humans.

Both organisms have often been isolated from such animals as pigs, birds, beavers, cats, and dogs. Only Y. enterocolitica has been detected in environmental and food sources, such as ponds, lakes, meats, ice cream, and milk. Most isolates have been found not to be pathogenic.

Name of Disease:

Yersiniosis

There are 3 pathogenic species in the genus Yersinia, but only Y. enterocolitica and Y. pseudotuberculosis cause gastroenteritis. To date, no foodborne outbreaks caused by Y. pseudotuberculosis have been reported in the United States, but human infections transmitted via contaminated water and foods have been reported in Japan. Y. pestis, the causative agent of " the plague," is genetically very similar to Y. pseudotuberculosis but infects humans by routes other than food.

Nature of Disease:

Yersiniosis is frequently characterized by such symptoms as gastroenteritis with diarrhea and/or vomiting; however, fever and abdominal pain are the hallmark symptoms. Yersinia infections mimic appendicitis and mesenteric lymphadenitis, but the bacteria may also cause infections of other sites such as wounds, joints and the urinary tract.

Infective dose:

Unknown. However, it is expected that the infective dose is relatively high.

Illness onset is usually between 24 and 48 hours after ingestion, which (with food or drink as vehicle) is the usual route of infection.

Diagnosis of Human Illness:

Diagnosis of yersiniosis begins with isolation of the organism from the human host's feces, blood, or vomit, and sometimes at the time of appendectomy. Confirmation occurs with the isolation, as well as biochemical and serological identification, of Y. enterocolitica from both the human host and the ingested foodstuff. Diarrhea is reported to occur in about 80% of cases; abdominal pain and fever are the most reliable symptoms.

Because of the difficulties in isolating yersiniae from feces, several countries rely on serology. Acute and convalescent patient sera are titered against the suspect serotype of Yersinia spp.

Yersiniosis has been misdiagnosed as Crohn's disease (regional enteritis) as well as appendicitis.

Associated Foods:

Strains of Y. enterocolitica can be found in meats (pork, beef, lamb, etc.), oysters, fish, and raw milk. The exact cause of the food contamination is unknown. However, the prevalence of this organism in the soil and water and in animals such as beavers, pigs, and squirrels, offers ample opportunities for it to enter our food supply. Poor sanitation and improper sterilization techniques by food handlers, including improper storage, cannot be overlooked as contributing to contamination.

Frequency of the Disease:

Yersiniosis does not occur frequently. It is rare unless a breakdown occurs in food processing techniques. In the USA the estimated incidents amount about 17,000 cases annually. Yersiniosis is a far more common disease in Northern Europe, Scandinavia, and Japan.

Complications:

The major "complication" is the performance of unnecessary appendectomies, since one of the main symptoms of infections is abdominal pain of the lower right quadrant.

Both Y. enterocolitica and Y. pseudotuberculosis have been associated with reactive arthritis, which may occur even in the absence of obvious symptoms. The frequency of such postenteritis arthritic conditions is about 2-3%.

Another complication is bacteremia (entrance of organisms into the blood stream), in which case the possibility of a disseminating disease may occur. This is rare, however, and fatalities are also extremely rare.

Target Populations:

The most susceptible populations for the main disease and possible complications are the very young, the debilitated, the very old and persons undergoing immunosuppressive therapy. Those most susceptible to postenteritis arthritis are individuals with the antigen HLA-B27 (or related antigens such as B7).

Food Analysis:

The isolation method is relatively easy to perform, but in some instances, cold enrichment may be required. Y. enterocolitica can be presumptively identified in 36-48 hours. However, confirmation may take 14-21 days or more. Determination of pathogenicity is more complex. The genes encoding for invasion of mammalian cells are located on the chromosome while a 40-50 MDal plasmid encodes most of the other virulence associated phenotypes. The 40-50 MDal plasmid is present in almost all the pathogenic Yersinia species, and the plasmids appear to be homologous.

Selected Outbreaks:

1976. A chocolate milk outbreak in Oneida County, N.Y. involving school children (first reported yersiniosis incident in the United States in which a food vehicle was identified). A research laboratory was set up by FDA to investigate and study Y. enterocolitica and Y. pseudotuberculosis in the human food supply.

Dec. 1981 - Feb. 1982. Y. enterocolitica enteritis in King County, Washington caused by ingestion of tofu, a soybean curd. FDA investigators and researchers determined the source of the infection to be an non-chlorinated water supply. Manufacturing was halted until uncontaminated product was produced.

June 11 to July 21, 1982. Y. enterocolitica outbreak in Arkansas, Tennessee, and Mississippi associated with the consumption of pasteurized milk. FDA personnel participated in the investigation, and presumptively identified the infection source to be externally contaminated milk containers.

A report of Yersinia enterocolitica incidents associated with raw chitterlings may be found in MMWR 39(45):1990 Nov 16