Scientists warn of Dutch Salmonella increase
Scientists have warned of a continuous increase in Salmonella infections in the Netherlands linked to the chickens stalling eggs.
Since mid-2023, the country has experienced a sustained increase in infections in Salmonella Enteritidis.
Infections increased from an annual average of 281 from 2017 to 2017 to 427 in 2023, and 401 in 2024. In the first six months of 2025, 209 cases were reported, against 180 during the same period in 2024. The ascent arrives at the same time as a 2.5 times increase in positive tests for salmonella in hen covers.
Although the increase is currently limited to the Netherlands, spreading to other European countries is possible due to the trade, travel and movements of poultry products.
Started with an epidemic
In the chicken farms that ponted the Dutch, the slaughter is not compulsory after the detection of Salmonella Enteritidis, but all the eggs of positive herds must go for treatment, including a heat treatment. After the production cycle, the house must be carefully cleaned and disinfected before the introduction of new hens.
According to the study, published in Eurosurvence review, the 2023 increase was largely due to a major epidemic linked to egg shells from positive herds treated insufficiently before being added to poultry foods.
This led to a generalized infection in the laying of laying hens and led to human cases by consuming contaminated eggs. The epidemic, which started in the first half of 2023, led to 151 cases in 2023, 27 in 2024 and 31 in 2025 to June.
In accordance with the EU rules, the hen herds that ponted adults are sampled at least every 15 weeks during the installation period. This surveillance has shown an increase in the Salmonella Enteritidis positive herds since May 2023, corresponding to the increase in human cases. In 2023, 74 positive herds were detected, followed by 81 in 2024 and 50 in the first half of 2025.
A causal analysis revealed that the number of positive herds considerably predicted the number of human cases to delays of 1 month, as well as 3 to 6 months.
Smaller clusters
After the epidemic, most of the cases in 2024 and 2025 occurred in smaller and more diverse clusters. Using the sequencing of the whole genome, scientists have identified 38 clusters not linked to the Travel in 2023, 42 in 2024 and 22 so far in 2025, with a median size of three cases for all years. This complicates surveys on epidemics and identification and control of the infection routes, researchers said.
The National Institute of Public Health and Environment (RIVM) created a response team at the beginning of 2025. The presence of many small clusters suggested a large model of transmission rather than a single epidemic of punctual source. Consequently, the recommended control measures have focused on reducing the prevalence and transmission of Salmonella Enteritidis throughout the industry.
Possible interventions include the increase in the frequency of tests in peel flocks to reduce the period during which the contaminated eggs are marketed, helping to limit human exposure or to accelerate the elimination of positive herds to lower infection pressure in the wider installation sector, by reducing the risk of propagation and reinfection of the farm to the farm.
The reasons for the sustained increase in Salmonella Enteritidis in the sector remain unclear. One possibility is the prolonged productive lifespan of the hens, which can increase their vulnerability as the immunity induced by the vaccine fades over time.
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