Almost 1,500 people have been sickened by Salmonella linked to Polish eggs in an outbreak that has lasted more than six years and affected 18 countries.

In total, 1,412 cases are associated with the outbreak: 532 confirmed and 166 probable infections since Feb. 2017 and 343 historical-confirmed and 367 historical-probable cases between 2012 and Jan. 31, 2017. No dates have been reported for four outbreak-confirmed infections.

More than 600 Salmonella Enteritidis cases have been recorded by the United Kingdom, almost 300 from the Netherlands and nearly 200 by Belgium. At least two deaths have been reported – a five year old child in Croatia and another patient in Hungary.

The European Centre for Disease Prevention and Control (ECDC) said most cases were reported during the summer months and due to reporting delays, additional infections are expected with onset in recent months.

Since an ECDC-EFSA outbreak assessment in Dec. 2017, 15 EU countries have reported 336 confirmed, 94 probable and three new historical-confirmed cases associated with the ongoing multi-country outbreak. In the same period, seven historical probable cases were excluded.

The 15 countries involved are Belgium, Czech Republic, Denmark, France, Hungary, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Poland, Slovenia, Sweden and the UK. Croatia, Finland and Greece have reported seven cases between them.

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Outbreak-confirmed cases belong to four different whole genome sequencing (WGS) clusters. Investigations identified eggs from Poland as the vehicle of infections in the multi-strain outbreak. Control measures were then implemented. However, new outbreak cases were notified in 2017 and in 2018 with similar magnitude and temporal patterns.

As part of the investigations, Polish eggs were traced back to three egg packing centers and 52 laying hen farms and 18 of these farms were positive for Salmonella enteritidis. Most of them, and the three packing centers, belong to one Polish consortium and are considered to be interlinked.

Control measures in Poland consisted of banning the sale of table eggs from positive farms and the packing centers until monitoring could demonstrate the absence of Salmonella. The ban did not apply to eggs used in the production of heat-treated items and was lifted in June 2017. New pullets were introduced after the culling of Salmonella-positive flocks and cleaning and disinfection of the poultry house.

A total of 112 confirmed or historical-confirmed cases were reported with travel history in an EU country during the incubation period.

Countries where infections likely took place were Poland with 25 cases from 2016 to 2018; Bulgaria with 22 cases from 2015 to 2018; Cyprus with 14 cases in 2016 and 2018; Portugal with 11 cases from 2015 to 2017; and Hungary with 10 cases from 2016 to 2018. Travel-associated cases were also reported with less than 10 cases per country. The patients’ travel history included Austria, Belgium, Greece, Italy, the Netherlands, Romania, Slovenia and Spain.

Based on analysis of travel-associated cases, public health officials say it is likely that more countries where molecular typing is not performed routinely for human Salmonella Enteritidis isolates are affected by the outbreak, including Bulgaria, Cyprus and Portugal.

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