PHOENIX —  This morning presenters gave an update on various recent outbreaks, including this past year’s red onions with Salmonella, deli meats with Listeria and peaches with Salmonella

Salmonella in red onions
Joyce Cheng with the Public Health Agency of Canada, walked session attendees through the Canadian side of the Salmonella Newport outbreak linked to red onions.

Cheng started by explaining how dealing with an outbreak and finding its source is a cooperative mission, and in this case there were multiple partners in both the epidemiologic investigation — Public Health Agency of Canada, U.S. Centers for Disease Control and Prevention (CDC), Provincial/State partners and local partners — and the food safety investigation — Canadian Food Inspection Agency (CFIA), Health Canada and U.S. Food and Drug Administration (FDA).

The outbreak detection started in three different places, two in Canada and one in the U.S. “So we had three outbreaks happening at the same time, but we weren’t sure if they were connected,” Cheng said. 

The initial epidemiological signals started to form a picture. Restaurant clusters, Canadian burgers and U.S. Mexican-syle restaurants pointed to some shared ingredients — onions, tomatoes and leafy greens. This led to the testing of these ingredients and the CFIA conducting traceback on red onions to Thomas International Inc.

Further confirmation came as U.S. clusters also traced back to Thomson International Inc. 

The case count totaled 515 in Canada and 1,127 in the U.S. In Canada 99 percent of those ill reported eating onions or meals containing onions and in the U.S. the number was 91 percent.

Diane Ducharme, a Consumer Safety Officer with the Produce Safety Network at Center for Food Safety and Applied Nutrition at the FDA, gave some insight to the U.S. side of the outbreak. Duchame talked about the traceback efforts of the FDA leading them to the fields where the onions came from.

The on-site Investigation of the onion fields found large amounts of bird and animal activity in the area as well birds and frogs in the irrigation water. These findings lead to the hypothesis that contaminated irrigation water used in a growing field in Holtville, CA, may have contaminated the onions.

Listeria monocytogenes in Deli Products
Amanda Conrad, a CDC epidemiologist, and Andrea Cote from the USDA’s FSIS, talked about three recent outbreaks linked to deli meats.

The 2018 country deli ham Listeria outbreak was the first Listeria outbreak linked to deli meats since 2005. The next came in 2019 from deli-sliced meats and cheeses, and the third in 2020 from italian style deli meats.

The presenters talked about the challenges of listeriosis and deli product investigations.

  • Investigations are more difficult due to the long incubation period (up to 70 days)
  • Often ill people are older and often have more trouble remembering specific foods they ate 
  • Food items of interest may not be on the standard Listeria initiative case report form
  • People who eat food from delis often eat many products including meats, cheeses and prepared salads
  • Potential for cross-contamination at retail establishments

Conrad and Cote pointed to the lessons learned from these outbreaks:

  • Deli meats and products sliced at the deli are ready-to-eat (RTE) and can contain Listeria monocytogenes that can cause serious illness
  • Cross-contamination creates challenges for determining the ultimate source of an outbreak
  • It is important to continue to communicate to consumers and retailers the risks of consuming and handling deli meats and other products sliced or served in deli settings

Salmonella Enteritidis infections linked to fresh peaches
Michael Vassar with the CDC and Asma Madad with the FDA presented an overview of the 2020 Salmonella outbreak linked to fresh peaches.

Vassar pointed to the usefulness of consumer surveys in finding an outbreak source. This is how evidence for pre-bagged peaches evolved.

  • 84 percent (21 of 25) of sick people interviewed ate peaches; significantly higher than a general population survey which showed 28 percent to 37 percent
  • 67 percent (10 of 15) reported per-bagged peaches; 80 percent (8 of 10) reported pre-bagged peaches from the same grocery store chain

The surveys later pointed to loose peaches as well:

  • 85 percent (29 of 34) ate fresh peaches
  • 43 percent (9 of 21) ill people reported buying bulk/loose peaches from several retail chains

Madad concluded: 

  • This Salmonella outbreak linked to peaches from the U.S represents a novel commodity/pathogen pair.
  • Adjacent animal operations were a likely contributing factor to the outbreak, with dust as one possible route of product contamination.
  • Adjacent almond orchards also have the capacity to generate significant dust that could potentially harbor Salmonella.
  • All farms should be aware of and assess risks that may be posed by adjacent land use as part of preventative measures.

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