According to the European Centre for Disease Prevention and Control,  1,412 cases have been found associated with this outbreak: 532 confirmed and 166 probable cases since 1 February 2017 and 343 historical-confirmed and 367 historical-probable cases between 2012 and 31 January 2017. In addition, no dates have been reported for four outbreak-confirmed cases, so they are unclassifiable as current or historical cases (Table 1).

Table 1. Distribution of cases by case classification and country, EU/EEA, February 2012 to November 2018 (n=1 420; 4 cases missing date of onset or sampling or receipt at reference laboratory), as of 12 November 2018

 Reporting country  Confirmed cases       Probable cases          Historical-confirmed cases Probable-confirmed cases   Total number of cases

Belgium          0          46        14        127      187

Croatia           0          0          4          0          4

Czech Republic         0          6          0          3          9

Denmark       16        0          6          2          24

Finland           0          0          0          1          1

France 21        0          8          0          29

Greece            0          0          0          2          2

Hungary        0          29        0          5          34

Ireland           12        0          4          4          20

Ireland           1          0          0          0          1

Italy    0          12        1          19        32

Luxembourg 4          0          5          0          9

Netherlands  8          25        90        164      287

Norway         22        18        11        32        83

Poland            25        0          0          0          25

Slovenia         0          7          3          0          10

Sweden          11        20        12        2          45

United Kingdom      412      3          185      6          606

Total   532      166      343      367      1408

                          698                    710 

Most outbreak cases were reported during the summer months. Due to reporting delays, additional cases are expected to be reported with onset in recent months.

A total of 112 confirmed or historical-confirmed cases were reported with travel history in an EU country during the incubation period and therefore were likely infected there. Countries where infections likely took place were Poland (25 cases identified from 2016 to 2018), Bulgaria (22 cases from 2015 to 2018), Cyprus (14 cases in 2016 and 2018), Portugal (11 cases from 2015 to 2017) and Hungary (10 cases from 2016 to 2018). Additional travel-associated cases were also reported (<10 cases per country) with travel history to Austria, Belgium, Greece, Italy, the Netherlands, Romania, Slovenia and Spain.

The 2016 and 2017 European outbreak investigations identified eggs originating from Poland as the vehicle of infection in this outbreak (ECDC/EFSA rapid outbreak assessments published in March and December 2017). Outbreak-confirmed cases belong to four different WGS clusters.