In total 147 cases have been reported across five European countries: the UK, Denmark, Finland, Germany and Ireland. The UK has been worst hit, with 129 outbreak cases. Finland has seen 15 sicknesses due to the Salmonella strain while Denmark, Germany and Ireland have all reported one incident, the European Food Safety Authority (EFSA) revealed.
While cases were detected as far back as 2014, the number of people falling ill peaked in April 2017 and 2018.
The outbreak was first detected in the UK using whole genome sequencing (WGS). All S. Agona isolates from the five countries are genetically close with a maximum difference of two alleles from any other single isolate by core genome multilocus sequence typing scheme (cgMLST) using the ECDC Enterobase pipeline.
The close genomic relationship and the distinct seasonal spring peaks suggest that cases are part of an intermittent common source outbreak, EFSA suggested.
The food safety body said test results suggest the outbreak could be linked to cucumbers. Seventeen S. Agona food isolates from 2018, detected in the United Kingdom, were found to be closely genetically related to the human strains. The food isolates were from cucumbers sampled during processing before and after washing and ready to eat food products containing cucumbers.
However, EFSA added that there is insufficient epidemiological information available on the consumption of contaminated products by humans to support the microbiological evidence provided by the isolation of the outbreak strain in food. The epidemiological investigations in the other affected countries did not generate any strong hypothesis about the vehicle or source of infection.
The contaminated samples were found at five plants owned by two different companies. Although the cucumbers used in all final contaminated products originated from Spain for a limited period, from November 2017 to April 2018, EFSA said no connection between supply chains was identified. The primary producers of cucumbers were different and cucumbers were delivered to different processing companies through different distributors in the UK.
The laboratory results for Salmonella in all cucumber samples, taken either at primary production level in Spain or during distribution to/within UK, were negative.
“Based on the information available, the microbiological evidence suggests RTE products containing cucumbers as a possible vehicle of infection but so far it has not been possible to identify the specific point in the production chain where the contamination occurred,” EFSA concluded. “Further investigations along the food chain are needed to identify the source of contamination.”