During a 4-year period, 4,448 human, animal, and environmental samples collected in New York State were tested for the presence of Yersinia enterocolitica or related species. A total of 339 isolates were identified as Yersinia and characterized according to source, species, biogroup, serogroup, and, in some instances, phage type. Four new biogroups of Y. intermedia were characterized. Of 149 human isolates, 120 (80.5%) were identified as Y. enterocolitica, and 29 were identified as either Y. intermedia (12.1%), Y. frederiksenii (5.4%), or Y. kristensenii (2.0%). Of the other 190 isolates, recovered from animals and the environment, 54 (28.4%) were Y. enterocolitica and 136 were either Y. intermedia (62.6%), Y. frederiksenii (4.7%), Y. kristensenii (3.7%), or an undescribed Yersinia species (0.5%). Two established human pathogenic strains of Y. enterocolitica were recovered: 59 isolates (37 from an outbreak) of "American strain" (serogroup 0:8, biogroups Nil6hn 2, Wauters 1, and Knapp and Thal 2, phage type X,) and 11 isolates of "Canadian strain" (serogroup 0:3, biogroups Nilehn 4, Wauters 4, and Knapp and Thal 1, phage type IXb). This was the first documented isolation of the Canadian strain in the United States. Isolates of other strains implicated in human disease (serogroups 0:4,33, 0:5, 0:6,31, 0:7,8, and 0:8) were also recovered from both human and nonhuman sources.

Gastrointestinal disorders of varying severity were observed in 239 (53%) of 455 campers and staff members at a coed summer camp in Sullivan County, New York, during July 1981. Five of seven hospitalized patients had appendectomies before the disease was recognized as yersiniosis. Yersinia enterocolitica serogroup O:8 (American strain) was isolated from 37 (54%) of 69 persons examined, including the head cook and 3 others of the 11-person kitchen staff. Of 48 food, water, and environmental samples collected from the camp area, Y. enterocolitica isolates belonging to the same serogroup and biogroup as the human isolates were recovered from dissolved powdered milk, a milk dispenser, and turkey chow mein. This laboratory finding supported the epidemiological data indicating a correlation between consumption of these foods and illness. Y. enterocolitica isolates of the same biogroup as the O:8 isolates but belonging to serogroup O:34 were also isolated from six campers and two samples of dissolved powdered milk. Pathogenicity studies on the Yersinia isolates were performed with three in vitro tests (calcium dependency, autoagglutination, and HeLa cell infection) and one in vivo test (intraperitoneal challenge of mice). Most of the serogroup O:8 human isolates and the chow mein isolate were positive in all four tests. Milk isolates of serogroup O:8 were positive in the in vitro tests but were relatively avirulent in mice, whereas serogroup O:34 isolates, regardless of source, were negative in all four tests.

Fecal specimens for Yersinia screening were obtained from a variety of wild mammals, birds, reptiles, fish, and invertebrates throughout New York state. One specimen from each of 1,426 animals was examined. A total of 148 isolates of Yersinia enterocolitica and related species were obtained from 133 (9.3%) of the animals. Y. enterocolitica was isolated from 100 (7%) of the animals tested, including 81 (10%) of 812 mammals and 19 (3.3%) of 573 birds. Y. intermedia, Y.frederiksenii, and Y. kristensenii were isolated from 39 (2.7%), 5 (0.35%), and 4 (0.28%) animals, respectively. The 81 Y. enterocolitica isolates from mammals belonged to 15 serogroups and included three pathogens: two isolates of typical serogroup 0:8, the "American strain," one from a gray fox (Urocyon cinereoargenteus) and one from a porcupine (Erethizon dorsatum); and one isolate of serogroup 0:3, bacteriophage type IXb, the "Canadian strain," from a gray fox. The most prevalent serogroups recovered from mammals were 0:6,31 (16 isolates) and 0:5,27 (6 isolates). The 19 isolates of Y. enterocolitica from birds belonged to nine serogroups and included one serogroup 0:6,31 isolate from a common grackle (Quiscalus quiscula) and two serogroup 0:5,27 isolates from great horned owls (Bubo virginianus).