Netherlands: Increase in Salmonella cases in humans and link to egg-laying sector
A new report published in Eurosurveillance presents an analysis of the recent surge in Salmonella Enteritidis (SE) infections in humans and laying hen flocks in the Netherlands between June 2023 and June 2025. The rise in cases is significant compared to pre-2023 levels and appears to be linked to widespread transmission within the poultry sector, particularly associated with contaminated eggshells used as a calcium source in poultry feed.
The article details epidemiological and genomic surveillance data on SE infections in humans, revealing a marked increase beginning in mid-2023. Human cases rose from an annual average of approximately 281 (2017–2019) to over 400 in 2023, with elevated levels persisting thereafter. Concurrently, a substantial rise in SE-positive laying hen flocks was observed, increasing from an annual average of 30 (2018–2022) to over 70 in both 2023 and 2024.
Whole genome sequencing confirmed that many of the identified case clusters were small and dispersed, indicating a diffuse transmission pattern rather than a single-point source outbreak. The investigation identified contaminated eggshells, insufficiently heat-treated prior to their incorporation into poultry feed, as the likely trigger for the initial spread. This route of transmission facilitated widespread dissemination across farms and led to subsequent human infections.
Eggshells, are a by-product of hatcheries or the food industry. They contain high levels of calcium carbonate and may offer slightly better calcium bioavailability than limestone, particularly when finely ground. However, they pose a potential microbiological risk, especially contamination with pathogens like Salmonella, unless properly cleaned, sterilized, and dried.
