Listeriosis Outbreak Tied to Frozen Vegetables Plagues Several Countries

The European Centre for Disease Prevention and Control (ECDC) have announced the investigation of a multi-country outbreak of listeriosis—a rare, but serious infectious disease caused by the bacterium Listeria monocytogenes—that has been linked back to frozen corn and potentially other frozen vegetables.

The outbreak has been occurring in 5 European nations—Austria, Denmark, Finland, Sweden, and the United Kingdom—since 2015. As of the latest ECDC update, 47 cases have been confirmed to be associated with this outbreak, with 9 of the infections resulting in death; these numbers represent a case fatality rate of 19%.

Isolates collected from 2017 season vegetable products were found to be closely related to the outbreak strain after whole genome sequencing was performed. Specifically, 13 samples collected from frozen corn, 8 samples collected from frozen vegetable mixes including corn, 1 taken from frozen spinach, and 1 collected from frozen green beans. Furthermore, only 1 isolate was reported from a frozen vegetable mix that had been produced in 2016 and 3 isolates were obtained from spinach products produced in 2018.

Furthermore, the ECDC reports that 2 isolates were collected from 2 environmental samples from 2 different plants based in France and Hungary that had been freezing and handling frozen vegetable products during the 2017 and 2018 production seasons.

As such, on June 2018, the Hungarian Food Chain Safety Office banned the marketing of frozen vegetable products that had been produced between August 2016 and June 2018 in addition to issuing recalls for their frozen corn, peas, beans, spinach, and sorrel products and ordering their withdrawal from shelves. All freezing activity at the plant was halted that month as well.

“The same strains of L. monocytogenes have been detected in frozen vegetables produced by the same Hungarian company in 2016, 2017, and 2018,” the European Food Safety Authority (EFSA) announced in a statement. “This suggests that the strains have persisted in the processing plant despite the cleaning and disinfection procedures that were carried out.

The EFSA warns that new cases could still potentially emerge due to the long incubation period of listeriosis (which can be as long as 70 days), the long shelf-life of frozen products, and the consumption of the products that had been purchased before the recalls were issued.

The clinical symptoms associated with the infectious disease include febrile gastroenteritis, invasive disease (such as sepsis, meningitis, or meningoencephalitis), and fetal infections. Prompt recognition of associated symptoms is especially important to avoid serious complications or even death; it is estimated that about 20% of cases are fatal. Health care providers should be on the lookout for fever, muscle aches, headache, stiff neck, malaise, ataxia, convulsions, and changes in mental status, such as confusion.

The ECDC-EFSA are currently working on determining the exact points of contamination. They will report more information pertaining to the investigation as it becomes available.