The United Kingdom has reported 11 cases of Salmonella this year as part of an outbreak traced to eggs from Poland that started in 2012.

The outbreak was part of a multi-country investigation in 2016 and linked to eggs imported from Poland. Control measures were taken in that country and internationally and all eggs sourced from implicated Salmonella contaminated farms were removed from the market.

After an initial decline, infections continued to be reported in the U.K. in 2017 and 2018, indicating not all sources of contamination had been eliminated. There were 421 cases of Salmonella Enteritidis linked to the outbreak in 2017 and 2018.

A Public Health England (PHE) spokeswoman told Food Safety News that findings have been shared with Europe and Poland.

“The results of the investigation implicating the Polish egg supply chain in this outbreak have been disseminated to the relevant EU and Polish authorities to enable control measures to be taken by the authorities in the EU and Poland, in line with EU regulations regarding Salmonella Enteritidis contamination in laying chicken flocks and we await the outcomes of this communication,” she said.

Some of the cases have been linked to consumption of Polish eggs that were used in various dishes and served at catering premises and Chinese restaurants.

Nick Phin, deputy director of the national infection service at PHE, said: “Public Health England has been working with the Food Standards Agency, public health and food safety authorities in the devolved administrations, and the Animal and Plant Health Agency to investigate an outbreak of Salmonella Enteritidis, which has been linked to eggs sourced from Poland. The results of the U.K.’s investigation have been communicated to the authorities responsible for public health and food safety in the EU so further control measures can be taken.”

Polish egg recalls

Three recalls have occurred this year in Poland because of detection of Salmonella on the surface of shell eggs. The latest was in May for eggs with the code 3-PL14271307 produced by Ferma Złote Jajko and packed at Ovos Sp. z.o.o.

In April, the same issue was found for eggs with code 3PL 02181303 produced by “Jajo–Wojciechowicz” Wojciech Wojciechowicz. One month before, eggs with code 3PL30051328K3 produced by Fermy Drobiu Woźniak and distributed by Jeronimo Martins Polska S.A. were recalled.

The European Centre for Disease Prevention and Control (ECDC) is not collecting outbreak data on a regular basis and the latest data was from an epidemiological updat in November 2018.

Overall, 1,412 cases are associated with the outbreak: 532 confirmed and 166 probable cases since February 2017, and 343 historical confirmed and 367 historical probable cases between 2012 and 31 January 2017.

Since 2012 and up to November 2018, the U.K. has recorded more than 600 cases, almost 300 are from the Netherlands and nearly 200 from Belgium. At least two deaths have been reported – a five year old child in Croatia and another patient in Hungary.

Outbreak-confirmed cases belong to four different whole genome sequencing (WGS) clusters. ECDC offers sequencing services for countries reporting probable cases of human Salmonella Enteritidis isolates with Multiple-Locus Variable number tandem repeat Analysis (MLVA) profiles 2-9-7-3-2, 2-9-6-3-2, 2-9-10-3-2, 2-10-6-3-2, 2-10-8-3-2 or 2-11-8-3-2.

Likely outbreak is ongoing

Routine WGS-based surveillance for Salmonella is not happening yet and monitoring is based on MLVA profiles associated with the outbreak. However, MLVA submissions have dropped as countries are moving to WGS.

only two isolates with the implicated MLVA types have been reported in the European Surveillance System (TESSy) since the November update.

“It is likely the outbreak is still ongoing, but we won’t have evidence on this until we collect new information. In order to have the updated case numbers we would have to contact the countries and ask for their WGS data. This will be done ahead of the next epidemiological update, for which we don’t have a date yet,” an ECDC spokeswoman told Food Safety News.

“Salmonella Enteritidis follows seasonal patterns and in previous winters there has been a low number of cases, while peaks were observed from June to October.”

The spokeswoman said in the last three years the agency has informed risk managers at national and European level that the outbreak was still ongoing.

“Since the beginning of the outbreak, ECDC has been liaising with relevant authorities in the affected EU/EEA countries, the European Food Safety Authority and the European Commission to facilitate the coordination of investigation and response measures,” she said.

Outbreak control is designated part of risk management, which is the responsibility of member states.

More than 1,000 cases in three years

A study published in The Lancet Infectious Diseases journal found 18 EU and EEA countries reported 838 confirmed and 371 probable cases between May 2015 and October 2018. A total of 509 cases were reported in 2016, after which the number steadily increased.

Two strains of Salmonella Enteritidis in human cases were also identified in Salmonella-positive eggs and primary production premises in Poland, confirming the source of the outbreak.

After control measures were implemented, case numbers decreased, but increased again in March, 2017, and the rise continued into 2018.

“The re-emergence of cases suggests that outbreak strains have continued to enter the food chain, although changes in strain population dynamics and fewer cases indicate that control measures had some effect. Routine use of WGS in Salmonella surveillance and outbreak response promises to identify and stop outbreaks in the future,” wrote researchers.

By Joe Whitworth