Almost 250 new infections have been recorded in a multi-country outbreak of Salmonella linked to eggs from Poland.

The European Centre for Disease Prevention and Control (ECDC) and European Food Safety Authority (EFSA) reported that as of January this year, 18 countries have reported 656 confirmed and 202 probable cases since February 2017.

There are 385 historically confirmed and 413 historical probable cases going as far back as 2012 making it the largest European Salmonella Enteritidis outbreak ever recorded. However, ECDC officials said the true extent of the outbreak was likely underestimated.

Since the last updat in November 2018, 248 new cases have been reported, of which 124 were /confirm/ied, 36 probable, 42 historical-confirmed and 46 historical-probable infections.

More than 1,600 sick since 2012
Belgium, Croatia, Czech Republic, Denmark, Finland, France, Greece, Hungary, Ireland, Italy, Luxembourg, Netherlands, Norway, Poland, Romania, Slovenia, Sweden and the United Kingdom have recorded 1,656 infections since 2012. The U.K. has the most with 688 confirmed and probable cases, Netherlands has 280, Belgium has 202 and Czech Republic has 111.

Information on hospitalization is available for 427 patients in 12 countries and 136 needed hospital treatment among the confirmed and historical-confirmed cases. Two historical confirmed deaths, a child and an elderly patient, were also reported.

In each year from 2016 to 2018, outbreak cases peaked in September, with large waves reported between late spring and early autumn. Such a large seasonal increase was not seen in 2019.

Epidemiological, microbiological and food tracing investigations have linked cases before 2018 to eggs from laying hen farms of a Polish consortium.

Despite control measures in 2016 and 2017, farms of the Polish consortium were positive in 2018 and 2019 with outbreak strains, suggesting persistent contamination, according to officials. Investigations on the laying hen production and feed supply chains did not find the possible origin of contamination.

One of the outbreak strains was found from 2017 to 2019 in primary production in Germany. This outbreak strain represents two-thirds of confirmed cases.

Investigations in U.K.
In September 2018, a cluster of nine confirmed cases was associated with the consumption of a RTE raw liquid egg-white drink distributed by Dr. Zak’s. Salmonella positive samples of RTE liquid eggs white from two batches matched those from this outbreak cluster.

Both batches were produced by a French company. One was produced with raw materials such as pasteurized white egg from a Spanish company. The other used raw materials from 13 German laying hen farms and 11 Dutch laying hen farms. An investigation of this outbreak showed positive batches were produced with eggs from Spain, the Netherlands and Germany, who all supplied Salmonella-free eggs to the French company.

On the same day as production of one of the contaminated batches, a different batch of liquid eggs was produced at the French company with eggs supplied by a Polish packing center from a Polish laying farm belonging to the Polish consortium. However, the possibility of cross-contamination was ruled out due to the different production line used with different equipment: tanks, filling machine, and because of heat treatment on packaged products.

Investigations in the U.K. identified 14 cases potentially part of the outbreak travelling to Cyprus and staying in the same place between end of May and end of June 2018. This site received eggs from a Polish laying farm through the Polish packing center and a Dutch wholesaler.

Polish action
Measures taken in 2016 and 2017, including depopulation of positive flocks, were not enough to eliminate contamination in the Polish consortium. So, the laying hen farms of this group were still positive for outbreak strains in 2018 and 2019.

Between August 2018 and December 2019, seven of 13 sampled Polish laying hen farms belonging to the Polish consortium tested positive for Salmonella Enteritidis. From November 2019 to January 2020, all flocks belonging to the Polish group were tested in accordance with Regulation 2160/2003 but Salmonella was not detected.

Polish authorities reported that all Salmonella Enteritidis positive flocks belonging to the Polish consortium were depopulated, including flocks found positive in May 2019. From 2015 to 2019, 16 laying hen farms, 13 of which belonged to the Polish consortium, were positive for at least one of the four SNP addresses causing human infections. Four rearing farms belonging to the Polish company were positive for Salmonella Enteritidis between January 2017 and July 2019.

ECDC officials said the outbreak was still ongoing and more infections were expected.

“Since no evidence has been provided that the source of contamination has been eliminated, it is expected that further infections will occur and that new cases will be reported in the coming months. Additional investigations are necessary to identify the source of contamination.”