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Seventeen food isolates matching the Salmonella outbreak strain linked to 147 illnesses were detected earlier this year in four plants of one company and the site of a different firm in the United Kingdom.
The Salmonella Agona food isolates were found to be closely genetically related to the human strains.
They were from cucumbers sampled during processing, before and after washing (11 isolates) and six were found in ready-to-eat food (RTE) products containing cucumbers.
Production continued at both companies as the affected cucumbers and associated RTE items containing them were no longer being produced.
Cucumbers used in all final contaminated products came from Spain between November 2017 and April 2018.
The company with positive samples from four plants told authorities it will use an alternative supplier in future.
The UK has 129 of the Salmonella Agona outbreak cases and Finland has 15. Denmark, Germany and Ireland have had one case each. The confirmed Irish case had a travel history to the UK prior to onset of symptoms.
A Food Standards Agency spokesperson told Food Safety News that it is trying to narrow down the likely source of the reoccurring outbreak with Public Health England.
“Evidence produced through whole genome sequencing of human cases suggests there is a link between a batch of cucumbers used in ready to eat products which may have been contaminated at a stage in the production chain,” said the spokesperson.
“Use of these specific cucumbers had already stopped before their identification as the suspected source and there has been a significant reduction in cases.”
Despite this claim of a reduction in cases, 122 have been recorded since January 2017. The other 25 infections occurred between 2014 and 2016.
The European Food Safety Authority (EFSA) and FSA refused to name the companies involved.
“The company whose ready to eat products tested positive stopped using the suspected contaminated cucumbers as a result. Naming and recalling them would not have helped customers as these products were already likely to be beyond their use by dates. We are not aware of any affected cucumbers from Spain or elsewhere to be currently on sale in the UK,” said the FSA.
The European Centre for Disease Prevention and Control (ECDC) warned there was a “high likelihood” that the outbreak strains will re-emerge in early 2019, as seen in the seasonal occurrence of cases in previous years.
In response, FSA said it would help ensure that a re-emergence of the outbreak does not happen with authorities in Spain and elsewhere in Europe and continue investigating with PHE to isolate the source.
In May 2018, Public Health England (PHE) reported a cluster of cases of Salmonella Agona, with isolates closely related by whole genome sequencing (WGS)-based analysis.
The majority of cases had sampling dates in 2017 and 2018 but the earliest case was reported in April 2014.
A spokeswoman for PHE told Food Safety News it has been investigating a number of linked Salmonella agona cases in the UK since last year.
“New case reports have significantly declined since May, when the suspected vehicle (cucumbers used in ready to eat products) was no longer supplied into the UK,” she said.
“As soon as the potential link to RTE products containing cucumbers as a possible vehicle became clear, the FSA was alerted and worked with the suppliers to stop the import of the products. It is not usual to alert the public to an outbreak in situations where the product has a very short shelf life, and importation and distribution of the product has already ceased.”
ECDC said there was not sufficient epidemiological information to support the microbiological evidence provided by the isolation of the outbreak strain from cucumbers.
When asked what epidemiological information was available, PHE said it was unable to comment on specific patient interviews or findings.
In May 2018, the FSA issued an RASFF notification regarding detection of Salmonella in 10 of 73 food samples of cucumbers.
This sampling in April at the first plant of the company during processing (before and after the cucumber washing stage) was part of the firm’s own checks.
The company notified FSA on April 16 and began investigating. The isolates were sent to the Salmonella Reference Laboratory at PHE and, following analysis of WGS data, were found to match the outbreak strain.
Asked about the month delay between being told and the RASFF notification, the FSA said it issued a RASFF, which requires detailed traceability information, as soon as there was sufficient evidence of the link between the human cases and it had strong evidence that it related to imported products.
A further sample of cucumbers during processing (unwashed) on April 11 at another site of the company was positive for Salmonella Agona. WGS analysis also confirmed this isolate matched the outbreak strain through analysis of WGS data.
Five Salmonella isolates had been previously detected at the company this year in five RTE products containing cucumbers collected between March 28 and April 5. These five isolates were confirmed as Salmonella Agona and matched the outbreak strain.
Workers at the firm remove the ends before transferring cucumbers to a wash tank dosed with sodium hypochlorite or peracetic acid, depending on the site.
No Salmonella Agona contaminated food samples were detected in Spain. Cucumber production of the Spanish primary producer is seasonal between November and April.
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