www.eurosurveillance.org | 05 Mar 2026
10 March 2026
A large-scale, prolonged outbreak of Salmonella Enteritidis (SE) in the Netherlands has highlighted a critical vulnerability in the food production chain: the use of inadequately processed eggshells in animal feed. Between June 2023 and September 2025, health authorities identified 227 outbreak cases through national genomic surveillance.
The investigation, utilizing Whole Genome Sequencing (WGS) and a case-control study, revealed that the outbreak consisted of two genetically related but distinct subclusters with different epidemiological profiles:
-Subcluster A (123 cases): Primarily linked to the consumption of barn eggs purchased at supermarkets.
-Subcluster B (104 cases): Strongly associated with the consumption of organic eggs.
The breakthrough in the investigation occurred in October 2023. An isolate from dried eggshells, collected as part of an internal monitoring program by an animal feed producer, was genetically linked to Subcluster A.
Further tracing revealed that eggshells from SE-positive laying hen farms were being used as a calcium source in poultry feed without undergoing sufficient heat treatment. Following these discoveries, testing frequency for laying hen flocks was significantly tightened. As of October 2025, younger hens are tested every 8 weeks (down from 15), and hens older than 65 weeks are tested every 4 weeks.
