Multi‐country outbreak of Listeria monocytogenes serogroup IVb, multi‐locus sequence type 6, infections linked to frozen corn and possibly to other frozen vegetables – first update

An outbreak of invasive Listeria monocytogenes infections confirmed by whole‐genome sequencing (WGS) and linked to frozen corn and possibly to other frozen vegetables has been ongoing in Austria, Denmark, Finland, Sweden and the United Kingdom since 2015. As of 15 June 2018, 47 cases were reported and nine patients died. WGS analysis of 29 non‐human L. monocytogenes isolates found them to be closely related to the multi‐country human cluster of L. monocytogenes serogroup IVb, multi‐locus sequence type 6. The non‐human isolates were obtained from frozen corn, frozen vegetable mixes including corn, frozen spinach products, frozen green beans and two environmental samples. The strong microbiological link between the human and the non‐human isolates is indicative of a common source related to frozen corn and other frozen vegetable mixes persisting in the food chain. Traceability information for the contaminated products pointed to the source of contamination in a Hungarian freezing plant. It is possible that frozen vegetables other than corn processed in this plant, could also be a vehicle of human infection. The information available confirms contamination within the Hungarian plant, but thorough sampling and testing are needed to identify the source of contamination at the plant concerned. On 29 June 2018, the Hungarian Competent Authority banned the marketing of all frozen vegetable products produced by the Hungarian plant, and ordered their immediate withdrawal and recall. This restrictive measure is likely to significantly reduce the risk of human infections and contain the outbreak. Any potentially contaminated frozen vegetables could still represent a possible risk to consumers until completely withdrawn and recalled. New invasive listeriosis cases may also be identified due to the long incubation period, the long shelf‐lives of these products, and potential consumption of frozen vegetable products bought by consumers before the recalls and eaten without being properly cooked.