European Listeria outbreak blamed on frozen corn

It’s been three years since a deadly listeriosis outbreak started in Europe, and outbreak investigators have said they’ve likely hammered down the cause: frozen corn.

An investigation report published last week by the European Food Safety Authority and the European Centre for Disease Prevention and Control said that frozen corn is the most likely source of Listeria monocytogenes in an outbreak that has affected at least five countries, including the United Kingdom, Austria, Sweden, Finland and Denmark.

All in all, 32 listeriosis cases have been confirmed as part of the outbreak since December of 2015, six of them resulting in death.

It’s unclear at what exact point on the food chain contamination occurred, but traceability information from three frozen corn samples led investigators to corn that was packed in Poland and processed in Hungary. Two additional non-human isolates from frozen vegetable mixes (that included corn) were traced back to the same Hungarian location. Investigators will continue to learn more, but tracking L. monocytogenes outbreaks can be tricky due to the pathogen’s long incubation period (up to 70 days).

Thanks to whole genome sequencing, investigators determined the exact serotype of Listeria that they were dealing with, and the likely food culprit. Using frozen corn samples, whole genome sequencing was used to reveal the entire DNA structure of the pathogen. With that information, it became possible to begin tracing where the bacteria came from by looking for the same strain in other food products.

About L. monocytogenes

L. monocytogenes is usually associated with ready-to-eat deli meats or hot dogs, but can crop up anywhere, including frozen vegetables. It’s a hardy bacteria that can grow even in colder conditions.

Listeriosis symptoms include fever, muscle aches, diarrhea and/or other gastrointestinal symptoms — although symptoms may not be the same across all individuals. Those who are pregnant may experience a fever, aches, fetal loss or other harm to their newborns (such a meningitis). Older individuals, or those with compromised immune systems, may also experience gastroenteritis or no symptoms at all.

Most people recover on their own without treatment, but younger, elderly and immunocompromised patients face bigger risks.

Listeriosis cases can be prevented when food producers exercise rigorous cleaning and monitoring programs, and when consumers keep their own kitchens clean, and always cook food to an adequate temperature.

Neogen offers many innovative tests for the detection of Listeria, including the revolutionary Listeria Right Now™ test as well as traditional methods.

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