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Notes from the Field: Yersinia enterocolitica Infections Associated with Pasteurized Milk --- Southwestern Pennsylvania, March--August, 2011

On July 22, 2011, a pediatric infectious disease physician reported a culture-confirmed case of Yersinia enterocolitica infection to the Allegheny County Health Department (ACHD), Pennsylvania. Two additional cases in Allegheny County with onset around the same time were identified by Pennsylvania's version of the National Electronic Disease Surveillance System aberration detection algorithm, which routinely evaluates disease reports, searching for unusual events. During March--August for the 3-year period 2008--2010, three cases of Y. enterocolitica infection had been reported in Allegheny County and a total of five in southwestern Pennsylvania. Subsequent review of the surveillance data identified 16 culture-confirmed patients with symptom onset during March 24--August 5, 2011. Patients were aged 1--75 years (median: 26.5 years). Seven patients (44%) were hospitalized; three were admitted to an intensive care unit.

All 16 patients reported drinking glass-bottled, pasteurized milk from dairy A; three patients also reported eating dairy A ice cream. Dairy A is certified by the Pennsylvania Department of Agriculture to pasteurize milk onsite. The dairy distributes 10,000 containers of milk weekly to approximately 650 households and 40 retail outlets and restaurants in southwestern Pennsylvania; 85% of the milk is distributed to homes and stores in returnable glass bottles, which are washed and sanitized by the dairy.

On July 27, 2011, dairy A voluntarily halted onsite production and distribution of products and advised home delivery customers and retail stores to dispose of their remaining products. On July 29, ACHD and the Pennsylvania Department of Health (PADOH) issued a press release advising of possible health risks associated with consuming dairy A milk and recommending disposal of any remaining milk. Consumers with symptoms of abdominal pain, diarrhea, and fever were advised to seek medical care. Patients with confirmed illness were advised to submit remaining dairy A products for testing. Cohort studies of families receiving home delivery of dairy A milk and of purchasers of dairy A milk from a single retail outlet are ongoing.

ACHD, PADOH, and the Pennsylvania Department of Agriculture conducted site visits to dairy A; milk and environmental samples tested negative for Yersinia. One unopened container of ice cream from the home of a patient with culture-confirmed illness tested positive for Y. enterocolitica, as did homemade yogurt made with dairy A milk in the home of an asymptomatic person. Yersinia cultured from the ice cream, from the homemade yogurt, and from stool samples from nine patients showed matching pulse-field gel electrophoresis (PFGE) patterns. On August 26, PADOH and ACHD issued another press release advising of possible health risks associated with consuming dairy A ice cream and recommending disposal of any remaining ice cream. The mechanism of milk and ice cream contamination remains unknown. Dairy A has resumed production and distribution following a Pennsylvania Department of Agriculture culture of a test batch of products that demonstrated no growth of Yersinia. No additional outbreak-associated cases of Yersinia have been reported since August 5.

Y. enterocolitica is a relatively infrequent cause of diarrhea and abdominal pain; approximately one culture-confirmed Y. enterocolitica infection per 100,000 persons is reported each year. Yersinia contamination of pasteurized milk is rare. In prior investigations, postpasteurization contamination with Yersinia was postulated (1,2). Yersiniosis can present as abdominal pain, acute mesenteric lymphadenitis mimicking appendicitis, fever, and systemic infection. Bloody diarrhea occurs in ≤25% of patients, but diarrhea might be absent in ≤33% (3). Diagnosis usually is made through stool or blood culture. Because Yersinia might not be detected using routine culture methods, specific testing to detect Yersinia should be requested when suspected (3).

Reported by

Ronald Voorhees, MD, Megan Casey, MPH, Sharon Silvestri, Gim Yee, Allegheny County Health Dept; Lydia Johnson, PhD, Pennsylvania Department of Agriculture; Stephen Ostroff, MD, Andre Weltman, MD, Kirsten Waller, MD, Maria Moll, MD, Atmaram Nambiar, MD, Pennsylvania Dept of Health. James Lando, MD, Career Epidemiology Field Officer; Allison Longenberger, PhD, Michael Gronostaj, MD, EIS officers, CDC. Corresponding contributor: Michael Gronostaj,, 412-228-0995.


  1. Greenwood MH, Hooper WL, Rodhouse JC. The source of Yersinia spp. in pasteurized milk: an investigation at a dairy. Epidemiol Infect 1990;104:351--60.
  2. Ackers M, Schoenfeld S, Markman J, et al. An outbreak of Yersinia enterocolitica O:8 infections associated with pasteurized milk. J Infect Dis 2000;181:1834--7.
  3. Heymann DL, ed. Control of communicable diseases manual. 19th ed. Washington, DC: American Public Health Association; 2008.

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