Yersinia Enterocolitica Remains a Potent Threat

By Irene V. Wesley, DrPH (Doctor of Public Health)

Yersinia enterocolitica
 is a bacterium which causes ~87,000 human cases of foodborne illness (yersiniosis) and 1,100 hospitalizations annually in the United States. Consumption of contaminated dairy products (milk and ice cream), water and vegetables (tofu) have caused human illness. Eating contaminated raw/undercooked pork is a major risk factor for infection. Yersiniosis results in diarrhea, fever and abdominal pains, mimicking appendicitis.
Y. enterocolitica is one of seven bacterial pathogens under FoodNet surveillance nationwide. In 2005, case rates (per 100,000 population) for yersiniosis varied from a high of 0.87 in California to a low of 0.11 in New Mexico.
Children are highly susceptible. The incidence in infants under 1 year of age is more than 40-fold higher than that of adults. Caregivers who fail to wash their hands while preparing “chitterlings” (pig intestines) or who feed raw pork to children can transmit Yersinia. 
Yersinia survives in ice for up to 448 days and at freezing temperatures in soil and manure. Temperature tolerance may explain its seasonal peaks in spring and fall and its higher prevalence in Northern Europe. The ability to grow in the cold is the basis for the “cold enrichment” method for its isolation (two weeks incubation at 4 degrees Celsius).
Y. enterocolitica is sensitive to irradiation, pasteurization and organic acids, but it withstands 5% sodium chloride. Growth within protozoa may protect it from the effects of chlorine. Y. enterocolitica is susceptible to heat, including hot water (80 C, 10-20 seconds) used during slaughterhouse cleanup, pasteurization (71.8 F, 18 seconds), and final internal cooking temperatures recommended for pork (160 F).
Y. enterocolitica is present in wildlife, cattle, sheep and clinically healthy pigs worldwide. In a survey of U.S. hogs, we detected Y. enterocolitica on 53.3 percent of the farms (41 of 77) and in 12.4 percent of hog fecal samples (345 of 2,793). At the retail level, Y. enterocolitica was isolated from 19.8 percent of packaged pork and in 11.5 percent of ground pork samples.
Pigs are the major livestock reservoir of human pathogenic serotypes O:3 and O:9 worldwide. In Scandinavia, antibodies to Y. enterocolitica serotype O:3 in slaughterhouse workers exceeded those in the general population, suggesting occupational risk from exposure to infected pigs. In Europe, clinical isolates of serogroups O:3 and O:9 have implicated consumption of raw or undercooked pork.
Bacteriological isolation methods can identify Yersinia in ~5 days to 2 weeks. More rapid PCR methods can detect one bacterium in a very small sample volume (5 ul) within ~48 hours.
“DNA fingerprinting” by PFGE has tracked its spread from pigs through the slaughterhouse to pork at the retail level. PFGE has also shown that sows transmit Y. enterocolitica via the fecal-oral route to piglets, which may contaminate the finisher house. These strains may persist in the finisher house for up to four years.
In summary, reduction of Y. enterocolitica is of importance to the pork industry because:
Pigs are the major animal reservoir of strains pathogenic to humans
Epidemiology links human yersiniosis to consumption of raw/undercooked contaminated pork
It is the only bacterial foodborne pathogen under FoodNet surveillance directly linked to pigs and pork.
Irene V. Wesley, DrPH, is a Microbiologist and Lead Scientist at the Preharvest Food Safety and Enteric Diseases Research Unit, USDA, ARS, National Animal Disease Center, in Ames, Iowa.