Detection of a Salmonella outbreak was helped by the fact that it was a novel serotype, according to researchers.
The salmonellosis outbreak had 47 confirmed cases in five European countries between March 2016 and April 2017. Seven additional infections were recorded between May and September 2017. An investigation suggested cross-contamination between different sesame seed lots at a large Greek processing company.
Researchers, writing in the journal Eurosurveillance, said the same outbreak pattern with a common serotype such as Enteritidis, would probably have been detected much later or not at all without high-discrimination typing data. The dates and geographical spread of illnesses outside Greece also resembled sporadic cases.
New family member? Salmonella Vari
In 2016, Greece reported an outbreak caused by a previously undescribed Salmonella serotype. Between March and May, 2016, the Greek National Reference Laboratory for Salmonella and Shigella in Vari, a suburb of Athens, detected 16 Salmonella isolates with the antigenic formula 11:z41:e,n,z15 sharing an indistinguishable PFGE profile.
The World Health Organization Collaborating Centre for Reference and Research on Salmonella at Institut Pasteur in France, confirmed a novel Salmonella serotype. The proposed name is Salmonella Vari.
Initial epidemiological investigations did not reveal a link between cases. Results of a case-case study provided evidence for tahini, a paste made from hulled, ground and toasted sesame seeds, as the probable vehicle of infection in Greece. However, it was not possible to identify a single product brand or place of purchase for the tahini and no food isolate was recovered for testing.
Between May 2016 and April 2017, Germany, Czech Republic, Luxembourg, and the United Kingdom reported salmonellosis infections with the novel serotype. Of 47 outbreak cases, 22 were in Greece; 13 in Germany; five in the Czech Republic; four in Luxembourg and three in the U.K. Of 26 with available information, 12 people were hospitalized.
Seven of nine interviewed patients, all five in Germany and two of four in Luxembourg, reported eating a particular brand of sweet sesame spread. After the sesame spread tested positive for Salmonella spp. in March 2017 it was recalled from the market.
Infections in countries spread was not distributed in
Seven other infections with the novel serotype were found between May and September 2017 with two in France; two more in Greece; and one each in Germany; Luxembourg and Serbia. Cross-contamination at the Greek company means other products could have been vehicles of infection. This might explain illnesses in countries where spread was not distributed such as Greece, Czech Republic, U.K., and Serbia.
In March 2016, sushi with sesame seeds was positive for the novel serotype via a company’s check at a private laboratory in the U.K., but follow-up testing did not identify Salmonella in any of the 24 ingredients, including three types of sesame seeds. Public Health England used ‘Salmonella unnamed’ for novel serotypes which caused a delay in finding the link between the sushi isolate and the outbreak.
Eight jars of sesame spread were collected in Germany. In Luxembourg, one pot was bought from a retailer. All nine jars were from the same lot, the only one on the market at that time, and the novel serotype was recovered from all of them. Salmonella spp. ranged from 77 to 160 colony forming units (CFU) per gram of sesame spread in three unopened jars.
The sesame spread positive for Salmonella had a best before the date of Feb. 1, 2018, and was produced in Greece with sesame seeds from Sudan. Seeds were harvested in Sudan in June 2015, arriving at the Greek company in November 2015. Tahini from these seeds was produced on March 18, 2016. It was stored in plastic pallet tanks until March 21, when part of it was mixed with other sesame spread ingredients: sugar, cottonseed oil, and soya lecithin.
Product was filled into glass jars which had ultraviolet treatment before filling, without the caps. Remaining sesame seeds were used to produce sesame oil and hulled as well as natural roasted seeds.
Sesame spread was delivered to Germany in March 2016 and distributed to Austria, Belgium, Estonia, France, Luxembourg, Portugal, and Switzerland. It was available in specialty health food stores and via online shops from March 2016.
Sesame seeds from Nigeria
In December 2016, a delivery of sesame seeds from Greece to Germany tested positive for Salmonella 11:z41:e,n,z15 during a company’s routine check-in Germany. The contaminated batch was sent back to the distributing firm in Greece.
These sesame seeds came from Nigeria, being harvested in January 2016. In September 2016, seeds arrived at the same Greek company. They were shipped to a company in Germany via seven deliveries but came from the same lot.
Seeds from this delivery never reached the consumer and could not explain the cases. The remaining six deliveries tested negative for Salmonella spp. and were further distributed.
The Greek company, a large sesame seed-processing firm that distributes seeds and products to various European countries, was visited by Greek authorities. All the firm’s checks for Salmonella spp. were negative.
It remains unclear how cross-contamination between the sesame spread and Nigerian sesame seeds was possible at the company and why sterilization was not effective in preventing salmonellosis infections.
As a consequence of the outbreak investigation, the European Commission included sesame seeds from Nigeria, Sudan and Uganda to the list of food of non-animal origin subject to increased official controls on imports due to possible Salmonella contamination.
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