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Study reveals Yersinia outbreak linked to pasteurized milk

Yersinia enterocolitica infections affected a youth summer camp and nearby community in Pennsylvania (US)

Over 100 people were sickened during a Yersinia outbreak linked to pasteurized milk in 2019, according to a study. Pasteurized milk may have been cross-contaminated by raw milk during the pasteurization process.

In July 2019, Yersinia enterocolitica infections affected a youth summer camp and nearby community in northeastern Pennsylvania (US).

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. The affected camp was for girls so 86 percent of patients were female.

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.

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.

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 dairy milked 75 cows and produced 17,500 to 24,500 pounds of milk per week. Nearly 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.

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.

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.