My client is a 55-year-old resident of Texas with no reported underlying illnesses when he developed listeriosis on July 16, 2024. Complications of that infection have severely and permanently compromised his cognitive function. His Listeria monocytogenes isolate has a sequence pattern highly similar (within 3 SNPs) to those isolated from at least six other patients (five isolated during April through December 2022, one in January 2024). These patients are part of a large cluster of patients with highly similar isolates.
CDC and FDA investigated illnesses in the cluster in 2017, 2018, and 2023. By March 2023, the cluster included 81 people in 23 states and 32 potato isolates; isolation dates spanned at least 8 years. The median allele range is 6 (range 0-36). CDC assigned the cluster a REP code (reoccurring, emerging, and persisting strains) in 2021. Initial hypotheses were ice cream, frozen meals, and frozen snack foods. The suspected product shifted to potatoes after Mexico reported 32 isolates from U.S. potatoes. FDA investigation led to a large potato packer in Colorado. They described the Colorado region as commonality among the farms providing potatoes. FDA determined that the packer supplied at least 13 manufacturers. Genetic diversity in the clinical and potato isolates suggested contamination at several manufacturing facilities. Many patients reported consuming frozen meals, frozen snack foods, and potato products. However, no brand or type of frozen food or product was identified. None of 45 samples of potato-containing frozen products yielded the outbreak strain. The source of this ongoing outbreak has not been determined.
The evidence is good that potatoes, maybe in frozen foods, are the ultimate source of the ongoing outbreak.
Here are the earlier reports.
https://www.marlerblog.com/files/2025/09/2025-3195-CARA-656-_Redacted.pdf
https://www.marlerblog.com/files/2025/09/2025-3195-CARA-775-_Redacted.pdf
https://www.marlerblog.com/files/2025/09/2025-3195-CARA-918-_Redacted.pdf