Eggs are the main food source of Salmonella outbreaks in Europe, according to a study.

From a list of 18 food sources, eggs and egg products were the most important source of salmonellosis outbreaks, followed by pork and general meat products.

Salmonella outbreak data in 34 European countries from 2015 to 2019 collected by the European Food Safety Authority (EFSA) were assessed. In Europe, Salmonella is the leading cause of outbreaks.

There was a significant increase in outbreaks in the period. This was driven by more reports in Eastern Europe, found the study published in the International Journal of Food Microbiology.

Most incidents in Eastern Europe
There were 939 outbreaks caused by Salmonella Enteritidis, 130 by Salmonella Typhimurium and its monophasic variant, 107 by other known serotypes, and 332 by unknown types.

After a significant decrease between 2008 and 2014, the incidence of salmonellosis stabilized in most European countries from 2015 to 2019. Identifying the main sources of outbreaks helps guide public health interventions.

Complex food categories such as bakery products, buffet meals, mixed food, other foods, sweets and chocolate, canned food products, and drinks were grouped together as unknown sources in the analysis because it was not possible to pinpoint the exact components responsible for infection.

In total, 1,508 Salmonella outbreaks were included in the analysis. Of these, 1,040 were caused by simple foods and 468 by unknown food sources. The number of ill people involved in outbreaks was not considered.

The majority of outbreaks were reported in Eastern Europe, followed by Southern, Western and Northern Europe, and the highest was 366 in 2018.

The top serotype associated with outbreaks was Salmonella Enteritidis. This might be related to the largest EU multi-country outbreak of Salmonella Enteritidis ever documented, which was linked to contaminated eggs from Poland and involved 14 countries since 2016, said researchers.

Regional and Salmonella type differences
The proportion of outbreaks attributed to unknown sources was largest in Eastern Europe. In Northern and Southern Europe, outbreaks caused by Salmonella Enteritidis decreased during the study period.

Eggs were the top food source in all regions but pork was the second most common source in Northern and Western Europe, and it was meat products in Eastern and Southern Europe. The amount of cheese and fish outbreaks decreased steadily over the years. 

Cereal products including rice and seeds and pulses, herbs and spices, and tap water were behind the fewest outbreaks.

The rate of salmonellosis attributed to eggs did not differ much over the study period. Eggs accounted for a higher proportion of outbreaks in Southern and Eastern Europe.

Outbreaks caused by Salmonella Enteritidis and other known serotypes were mostly attributed to eggs, whereas those caused by Salmonella Typhimurium and the monophasic variant were mainly traced to pork.

An increasing trend in Salmonella outbreaks can also be explained by the wider use of advanced molecular methods, such as whole genome sequencing (WGS), for outbreak detection and source tracing. This has likely helped in identifying more clusters of cases in routinely collected Salmonella surveillance data, said the study.

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