Salmonella in Vegan Cashew Brie: A Four-State Outbreak Caught Early by Genome Sequencing, 2021

On March 30, 2021, in its weekly review of sequenced bacteria, the Tennessee Department of Health spotted two closely related Salmonella Duisburg isolates. Both patients had eaten the same brand of cashew brie — a vegan alternative to brie cheese — at the same restaurant.

A search of the National Center for Biotechnology Information (NCBI) Pathogen Detection Isolates Browser found three more close genetic matches, two in California and one in Florida. California confirmed one of its patients had eaten the same cashew brie; the Florida patient followed a vegan diet. A multistate investigation began.

The outbreak

A case was an infection with one of four outbreak strains (identified by whole-genome sequencing, WGS) that began between December 1, 2020, and May 9, 2021.

Cases by illness onset, December 2020–May 2021. CDC

20 people in four states were infected:

Patients' median age was 26 (range 1–72); 65% were female. Five were hospitalized; none died. Of 19 interviewed, 15 had eaten the same brand of cashew brie in the week before falling ill.

The source

Officials collected 36 samples — ingredients, products in process and finished, and swabs from the only facility making the cashew brie. 23 (64%) yielded 51 Salmonella isolates:

Sequencing showed that the S. Chester and S. Urbana found in the products matched the patients' infections. The maker voluntarily recalled all its cashew brie.

Food testing and the FDA traceback pointed to the cashews as the likely source. The cashews had had no lethality treatment — a step such as pasteurization or irradiation that kills pathogens — before processing. The FDA worked with the cashew supplier to get potentially contaminated nuts off the market, and the supplier made corrective changes.

Lessons

• Outbreaks from raw nuts and seeds are well documented, and cashew cheese has caused Salmonella outbreaks before. Skipping a lethality step for ingredients raises the risk in ready-to-eat foods that people assume are safe.
• Two people sick after the same unusual food at the same restaurant, plus a rare serotype, gave investigators an early lead.
• Open access to WGS data through NCBI let the investigation start before the outbreak was big enough for standard multistate detection methods to flag it.
• With Salmonella in 95% of retail samples, fast detection, investigation and recall prevented more illness.

Sources

Based on Lewis K, Vasser M, Garman K, et al., "Notes from the Field: Multistate, Multiserotype Outbreak of Salmonella Infections Linked to Cashew Brie — United States, 2021," MMWR volume 72, number 21, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The report says S. Typhimurium was found in the cashew brie in one place and only in patients in another, so which strains were found in the product is limited here to the two it confirms.