The United States Department of Agriculture’s (USDA) Food Safety and Inspection Service (FSIS) routinely monitors clusters of illnesses to determine if FSIS-regulated products may be the source of food-borne illnesses.  FSIS posts information on active outbreak investigations to a table on its website when there is compelling evidence that an FSIS-regulated product is the source.  The primary pathogens involved in FSIS outbreak investigations are Salmonella, Shiga toxin–producing Escherichia coli (STEC), Listeria monocytogenes (Lm), and Campylobacter.

In a November 19, 2021 Constituent Update, FSIS announced that it has posted on its website an after-action review report for the investigation of a 2018 multi-state outbreak of Lm illnesses associated with ready-to-eat (RTE), Asian-style pork patty products that resulted in 4 hospitalizations.  Whole genome sequencing (WGS) analysis of bacterial isolates from routine FSIS product and environmental samples indicated the historical presence of the outbreak strain at a single FSIS-regulated establishment.  The Investigation further revealed that the pork patty products were cooked using a process that was not validated to ensure all pieces were thoroughly cooked, and there was a history of Lm harborage and opportunities for contamination after cooking that were not considered by the establishment.

The Lm outbreak linked to pork patties was only the second reported multistate outbreak of listeriosis linked to a FSIS-regulated product since 2005.  Nevertheless, as noted in the investigation report, FSIS may consider an update of Directive 10240.4 (Verification Activities for the Lm Regulation and the RTE Sampling Program) to include additional instructions for inspection personnel when verifying if a product is exposed to the environment after undergoing a cooking step.