Sources and trends of human salmonellosis in Europe, 2015-2019: An analysis of outbreak data

Salmonella remains a major cause of foodborne outbreaks in Europe despite the implementation of harmonized control programmes. Outbreak data are observed at the public health endpoint and provide a picture of the most important sources of human salmonellosis at the level of exposure. To prioritize interventions, it is important to keep abreast of the sources and trends of salmonellosis outbreaks. The objective of this study was to determine the main food sources and recent trends of Salmonella outbreaks in Europe. Salmonella outbreak data from 34 European countries in 2015-2019 were obtained from the European Food Safety Authority (EFSA). For the source attribution analysis, implicated foods were categorized according to EFSA's zoonosis catalogue classification scheme. An established probabilistic source attribution model was applied using the information on the implicated foods, overall and by region and serotype. To assess significant trends in outbreak occurrence, overall and by region and serotype, mixed-effects Poisson models were used. Overall, the most important food source of salmonellosis outbreaks was eggs (33 %, 95 % Uncertainty Interval [UI]: 31-36 %), followed by pork (7 %, 95 % UI: 6-8 %), and (general) meat products (6 %, 95 % UI: 5-8 %). While eggs were the most important food source in all regions, pork was the second most common food source in Northern and Western Europe, and (general) meat products in Eastern and Southern Europe. Outbreaks caused by S. Enteritidis (SE) and other known serotypes (other than SE and S. Typhimurium and its monophasic variant [STM]) were mostly attributed to eggs (37 %, 95 % UI: 34-41 % and 17 %, 95 % UI: 11-25 %, respectively), whereas outbreaks caused by STM were mainly attributed to pork (34 %, 95 % UI: 27-42 %). Overall, there was a significant increase in the number of outbreaks reported between 2015 and 2019, by 5 % on average per year (Incidence Rate Ratio [IRR]: 1.05, 95 % Confidence Interval [CI]: 1.01-1.09). This was driven by a significantly increased number of outbreaks in Eastern Europe, particularly those caused by SE (IRR: 1.15, 95 % CI: 1.09-1.22), whereas in Northern and Southern Europe, outbreaks caused by SE decreased significantly from 2015 to 2019 (IRR: 0.72, 95 % CI: 0.61-0.85; IRR: 0.70, 95 % CI: 0.62-0.79, respectively). Regional, temporal and serotype-associated differences in the relative contributions of the different sources were also observed.