# Two Concurrent Outbreaks of Listeria monocytogenes Infections Linked to Packaged Salads, United States, 2014–2022

## TL;DR

Two separate outbreaks of Listeria infections linked to packaged salads occurred over several years in the U.S., causing serious illnesses and highlighting the need for thorough food safety investigations.

## Contribution

The study identifies two distinct, long-term Listeria monocytogenes outbreaks linked to packaged salads and emphasizes the importance of coordinated sampling in outbreak detection.

## Key findings

- Two genetically unrelated Listeria outbreaks were linked to packaged salads from different firms.
- Outbreaks caused 30 illnesses, 27 hospitalizations, and 4 deaths over 8 years.
- Routine sampling and collaboration were crucial in solving the outbreaks.

## Abstract

We describe 2 genetically unrelated outbreaks of Listeria monocytogenes infections (outbreak A and outbreak B) linked to packaged salads from 2 different firms that were investigated simultaneously in 2021. Combined, the outbreaks caused 30 illnesses, 27 hospitalizations, and 4 deaths over 8 years. Those investigations led to recalls of product from 2 different firms and highlight how L. monocytogenes contamination can persist for long periods and cause illnesses over many years. Outbreak A was investigated 3 times with illnesses occurring over 8 years, whereas illnesses in outbreak B occurred over 5 years. Both outbreaks illustrate the importance of routine and epidemiologically directed sampling by state partners, without which these outbreaks likely would have gone unsolved. The outbreaks were the second and third multistate outbreaks of listeriosis linked to packaged salads, providing further documentation of the potential for L. monocytogenes infections from consumption of contaminated packaged salads.