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Two Concurrent Outbreaks of Listeria monocytogenes Infections Linked to Packaged Salads, United States, 2014-2022
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.
Insights
Two Listeria monocytogenes outbreaks linked to packaged salads caused 30 illnesses and 4 deaths over several years. Persistent contamination highlights the need for ongoing surveillance to prevent long-term public health risks from contaminated food products.
Area of Science:
- Foodborne Illness Epidemiology
- Microbial Contamination
Background:
- Two genetically distinct outbreaks of Listeria monocytogenes infections were identified in 2021.
- These outbreaks were linked to packaged salads from two separate companies.
Purpose of the Study:
- To describe the epidemiology and characteristics of two multistate Listeria monocytogenes outbreaks.
- To highlight the persistence of Listeria monocytogenes contamination in food products over extended periods.
- To emphasize the importance of routine and targeted sampling in outbreak investigations.
Main Methods:
- Simultaneous investigation of two genetically unrelated Listeria monocytogenes outbreaks.
- Epidemiological data collection and analysis to track illness onset and duration.
- Food product sampling and testing to identify contamination sources.
Main Results:
- Combined, the outbreaks resulted in 30 illnesses, 27 hospitalizations, and 4 deaths over 8 and 5 years, respectively.
- Product recalls were issued for both implicated companies.
- Outbreak A involved illnesses spanning 8 years across three separate investigations, while Outbreak B had illnesses over 5 years.
Conclusions:
- Listeria monocytogenes contamination in packaged salads can persist for years, leading to prolonged outbreaks.
- Routine and epidemiologically guided sampling by state partners are crucial for detecting and resolving such outbreaks.
- These findings reinforce the risk of listeriosis from consuming contaminated packaged salads.
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