More than 100 people were sickened during a Yersinia outbreak linked to pasteurized milk in 2019, according to a study. Raw milk may have cross-contaminated pasteurized milk during the pasteurization process.

Yersinia enterocolitica infections affected a youth summer camp and nearby community in northeastern Pennsylvania in July 2019.

Researchers identified 109 cases, 48 confirmed and 61 probable. Ninety-two were campers and camp staff while 17 were in the community. Yersiniosis is not a reportable condition in Pennsylvania, although there are plans to make it one, which delayed outbreak identification and start of the investigation, said the study published in the journal Foodborne Pathogens and Disease.

onset dates were June 7 to July 26 and the median patient age was 15 years old. The affected camp was for girls so 86 percent of patients were female.

Camp and community link
Symptoms mainly included abdominal pain or cramps, then fever, and headache. Several patients also had non-bloody diarrhea. Seven people were hospitalized but no deaths were reported.

Initially, a youth summer camp reported Yersinia enterocolitica cases to the Pennsylvania Department of Health (PADOH) among four campers and staff. Additional Yersinia cases in residents unconnected with the camp were recorded by the local hospital laboratory.

In July 2019, PADOH advised people who purchased milk from Creamworks Creamery in Waymart, Wayne County, to not drink it or use it in cooking as it may contain Yersinia enterocolitica.

During interviews, two unrelated community members reported consuming pasteurized milk from the small dairy in northeast Pennsylvania. The camp owner said the dairy provided weekly milk shipments. It had sent 214 gallons of pasteurized milk in five weekly shipments to the camp by mid-July.

Among 37 patients, 31 had consumed Creamworks Creamery milk. It was the only shared exposure identified between the camp and community. Campers were not interviewed and not all staff completed a cohort questionnaire.

Inspection findings
PADOH and the Pennsylvania Department of Agriculture held an emergency inspection of the dairy on July 17 and the firm ceased distribution and recalled all milk. Before reopening, steps included a herd check by a licensed veterinarian, equipment cleaning and sanitation, and replacement of pasteurizer plates.

Inspectors didn’t find significant sanitary issues at the dairy. However, the gasket sealing the bulk milk tank was worn and needed replacing. Pasteurization records indicated proper temperatures were reached. The pasteurizer was purchased used 10 years previously.

The dairy milked 75 cows and produced 17,500 to 24,500 pounds of milk per week. about 3,500 pounds was pasteurized on site weekly with a high-temperature short-time pasteurizer. Products were sold to 22 clients, including small businesses and retailers and sold at a farm stand. The remaining unpasteurized milk was collected by a local cooperative that pasteurized and distributed it.

Search for source
Yersinia enterocolitica was isolated from all three unpasteurized milk samples from the bulk milk tank. It was not found in any of the unopened pasteurized milk, environmental, or well water samples. Most milk samples tested were collected and pasteurized in mid-July, almost two weeks after the peak number of Yersinia enterocolitica cases.

Raw milk may have cross-contaminated pasteurized milk during the pasteurization process or contamination of the environment could have resulted in post-pasteurization contamination of pasteurized milk, according to the study.

Seven clinical samples, five from campers and camp staff and two from community members, yielded Yersinia enterocolitica. The human and milk isolates were indistinguishable by whole genome sequencing.

Researchers could not find the pathogen’s origin at Creamworks Creamery but it is possible pigs or wildlife near the dairy were a potential source of Yersinia enterocolitica. Scientists were unable to test pigs before they were removed from the dairy or pasteurizer plates for wear and leaks.

“We recommend governmental agencies and small dairies conducting on-site pasteurization collaborate to develop additional outbreak prevention strategies. In addition, we recommend research partners continue to develop sensitive and rapid laboratory techniques to identify Yersinia enterocolitica in nonclinical samples,” they said.