Ongoing 5-year Salmonella outbreak sickens 1,000 from 16 countries

Eight countries report almost 300 new cases in Salmonella outbreak

By Joseph James Whitworth

- Last updated on GMT

Picture: iStock/studioaraminta. One hypothesis is persistent contamination of 2 or more sites with Salmonella strains detected in the 2016 outbreak still circulating at farm level in Poland
Picture: iStock/studioaraminta. One hypothesis is persistent contamination of 2 or more sites with Salmonella strains detected in the 2016 outbreak still circulating at farm level in Poland

Related tags Eggs Salmonella Sweden

Cases in a multiyear and multi country outbreak of Salmonella in eggs linked to Poland have seen a new peak after control measures had led to a decline.

From February to late November, eight countries reported 196 confirmed cases of Salmonella Enteritidis and 72 probable infections.

The UK has reported the most cases (166 confirmed and three probable). Norway has 30, Sweden (24), Belgium (23), Netherlands (12), France (five), Czech Republic (three) and Luxembourg (two).

Five years, 16 countries and 1,000 cases

A total of 340 historical confirmed and 374 historical probable cases were reported before February 2017 by 16 countries (the above eight countries plus Croatia, Denmark, Finland, Greece, Hungary, Ireland, Italy and Slovenia). Bulgaria and Portugal also appear to be affected.

A five-year-old child died in Croatia and Hungary also reported a fatal case. Authorities believe the outbreak began in 2012.

Who is (or are) the source(s)?

The NCAE (Nederlandse Controle Autoriteit Eieren) said Dutch cases came from eggs from Polish firms named as Fermy Drobiu Woźniak (Wozniak Poultry Farms), Specjalistyczne Gospodarstwo Rolne, Ferma Drobiu Maciej Kubiaczyk and Ovotek Sp. z o.o. Fermy Drobiu Woźniak was named as a supplier of contaminated eggs in 2016 by authorities. However, the firm told us testing by an accredited lab did not find Salmonella.

New outbreak cases increased after February this year and peaked in September. In the same month, a new cluster was detected in Sweden and a link with eggs from Poland was reported.

The peak in September saw 58 confirmed and 16 probable cases.

The European Centre for Disease Prevention and Control (ECDC) said some positive farms in the 2016 outbreak are epidemiologically or microbiologically linked to positive food sampled in Norway and the UK.

“No detections of S. Enteritidis have been reported in any farms identified in the present outbreak as the possible sources of contaminated eggs or in the holdings supplying the mentioned farms. This supports the hypothesis that there is persistent contamination of two or more premises with the Salmonella strains detected in the 2016 outbreak still circulating at the farm level in Poland.”

Contamination traced to Polish packing centres and laying hen farms

Cases steadily decreased from the end of 2016 to start of 2017 due to extended control measures in Poland in autumn 2016.

Testing through whole genome sequencing (WGS) shows the isolates are part of four distinct but related genetic clusters.

Two Polish barns from one farm were banned from placing eggs on the market earlier this year except when they are sufficiently heat treated to inactivate microorganisms.

Official samples on eggs, faeces and dust collected after re-population in the two barns between January and June were negative for S. Enteritidis and the ban was lifted in June.

Investigations last year traced Polish eggs back to three egg packing centres and 52 laying hen farms. Eighteen of these farms were positive for S. Enteritidis.

Sweden and Norway traceback

In an outbreak in August in Sweden, eggs were purchased in stores, which bought them from a Swedish mobile retailer that operates with two names and regularly receives eggs from a Polish wholesaler.

Eggs were traced to a different Polish packing centre than those involved in the previous outbreak. However, Polish authorities said distribution of eggs from this packing centre involved the wholesaler.

Investigations showed eggs linked to cases were traced back to one packing centre and two laying hen farms in Poland.

In Norway, eggs positive for S. Enteritidis at processing company level were delivered from another Polish packing centre (one of three involved in the previous outbreak) and a laying hen farm in Poland.

Eggs came from a farm involved in the previous outbreak and following positive results the Norwegian processing company has stopped purchasing eggs from Poland.

Despite genetic closeness of food isolates sampled in Sweden and Norway, no epidemiological link has been found between those Polish food business operators (packing centres and farms) in Swedish and Norwegian investigations.

UK investigation

Investigations into 155 confirmed cases in the UK since February identified seven catering premises in England.

Four of the seven sourced eggs from the same packing centre in UK which sourced eggs from countries, including Germany, Poland, Spain and the UK.

For some cases eggs probably consumed were identified and traced back to a laying hen farm in Poland different from the farms in the Swedish and Norwegian assessments.

Multiple locus variable-number tandem repeat analysis (MLVA) profiles associated with the four genetic clusters and denoting probable cases are 2-9-6-3-2, 2-9-7-3-2, 2-9-10-3-2, 2-10-6-3-2, 2-10-8-3-2 and 2-11-8-3-2. A seventh MLVA type (2-10-7-3-2) in isolates from the Swedish cluster in September was not included in the case definition.

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