Frozen corn is the likely source of an outbreak of Listeria monocytogenes which has affected five EU Member States (Austria, Denmark, Finland, Sweden, and the United Kingdom) since 2015. This is the conclusion of a rapid outbreak assessment published today by EFSA and the European Centre for Disease Prevention and Control (ECDC). As of 8 March 2018, 32 cases including six deaths had been reported.

Whole genome sequencing was used to define the multi-country outbreak of L. monocytogenes serogroup IVb, multi-locus sequence type 6 and to identify the implicated food source.

Investigations point towards frozen corn packed in Poland and processed and produced in Hungary. The report recommends further investigations to identify the exact point of contamination in the food chain.

Food business operators in Poland, Finland, Sweden and Estonia have withdrawn and recalled the implicated products. These measures are likely to reduce the risk of human infections in these countries.

However, new cases may be identified due to the long incubation period of listeriosis (up to 70 days), the long shelf-life of frozen corn products and the potential consumption of frozen corn bought before the recall was implemented.

To reduce the risk of L. monocytogenes infection from frozen corn, consumers should adequately heat frozen vegetables that are not ready-to-eat products. This applies especially to consumers at the highest risk of contracting listeriosis – such as the elderly, pregnant women, new-borns and adults with weakened immune systems.

What is a rapid outbreak assessment?

Coordination at EU level is crucial when there are multi-country foodborne outbreaks. One aspect of this coordination is the production of a rapid outbreak assessment (ROA) by EFSA and ECDC in close cooperation with affected countries.

The ROA gives an overview of the situation in terms of public health and identifies the cause of the infections. It also includes trace-back and trace-forward investigations to identify the origin of the outbreak and where contaminated products have been distributed. These help to identify measures that will prevent further spread of the outbreak.