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Findings highlight vulnerabilities in current poultry control due to regulatory tolerance for Campylobacter in fresh poultry 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two concurrent Campylobacter jejuni clones causing large outbreaks, Denmark, July to October 2025  \nGuido Benedetti¹ , Gitte Sørensen² , Ana Paula Finatto Canabarro1,3 , Emily Dibba White1 , Tine Graakjær Larsen¹ , Susanne Schjørring² , Eva Møller Nielsen² , Luise Müller¹ , Steen Ethelberg , Katrine Grimstrup Joensen2  \n1. Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark  \n2. Department of Bacteria, Parasites and Fungi, Statens Serum Institut, Copenhagen, Denmark  \n3. ECDC Fellowship Programme, Field Epidemiology path (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden  \n4. Department of Public Health, Global Health Section, University of Copenhagen, Copenhagen, Denmark  \nCorrespondence: Katrine Grimstrup Joensen ([knj@ssi.dk](knj@ssi.dk))  \nCitation style for this article:  \nBenedetti Guido, Sørensen Gitte, Canabarro Ana Paula Finatto, White Emily Dibba, Larsen Tine Graakjær, Schjørring Susanne, Nielsen Eva Møller, Müller Luise, Ethelberg Steen, Joensen Katrine Grimstrup. Increased severity of two concurrent Campylobacter jejuni clones causing large outbreaks, Denmark, July to October 2025. Euro Surveill. 2025;30(47):pii=2500856. [https://doi.org/10.2807/1560-7917. ES.2025.30.47.2500856](https://doi.org/10.2807/1560-7917. ES.2025.30.47.2500856)  \nArticle received on 13 Nov 2025 / Accepted on 27 Nov 2025 / Published on 27 Nov 2025  \nIn July–October 2025, two concurrent Campylobacter jejuni outbreaks (clones ST49\\#3 and ST52\\#4) with 112 notified cases were detected through Denmark’s whole genome sequencing surveillance programme. The outbreaks were clinically severe: 45 (40%) infected individuals were hospitalised and 16 (14%) had bacteraemia. We estimated 900 laboratoryconfirmed outbreak cases. Both outbreaks originated from Danish-produced chicken meat. These outbreaks reveal the vulnerabilities in the current prevention and control framework given by the regulatory tolerance for Campylobacter in fresh poultry meat.  \nIn July–October 2025 we identified two concurrent Campylobacter jejuni outbreaks of cluster type ST49\\#3 and ST52\\#4 (Danish nomenclature) through the national whole genome sequencing (WGS) surveillance in Denmark. The two outbreaks were notable in severity and magnitude, and they were traced to Danish chicken meat. We report on the occurrence, progression and characteristics of these outbreaks to shed light on the persistent problem of contaminated chicken meat and its implications for public health.  \nSetup and identification of the clusters  \nIn Denmark, around 5,000 laboratory-confirmed Campylobacter cases are notified yearly through the national surveillance system with each speciesspecific infection recorded once per individual in any 6-month period [1] .  \nSince 2019, Statens Serum Institut (SSI) has performed national WGS-based surveillance, covering 10–15% of confirmed Campylobacter cases [2] . Through the platform for national sequence-based surveillance of food-borne infections (SOFI), bacterial genomes from  \nhuman cases are routinely analysed and compared with genomes generated in the Danish Veterinary and Food Administration’s (DVFA) surveillance of food and animal sources.  \nDuring summer 2025, ST49\\#3 and ST52\\#4 rapidly expanded and were identified countrywide, prompting intensified microbiological and epidemiological investigations. Both clones had been detected in patients and Danish-produced chicken meat in previous years.  \nRoutine surveillance triggers an investigation when ≥ 10 genetically related isolates are detected within 90 days. The threshold was reached for ST49\\#3 on 2 September (week 36) and for ST52\\#4 on 12 August (week 33).  \nMicrobiological and epidemiological profile of the clusters  \nBetween 1 July and 15 October, 2,855 human campylobacteriosis cases were notified in Denmark, with 355 (12%) Campylobacter isolates received from Danish clinica","cbCaieWSDkCv932T","https://ap.wps.com/l/cbCaieWSDkCv932T","pdf",490878,"English","# Setup and identification of the clusters\n# Microbiological and epidemiological profile of the clusters\n## Definition of Campylobacter jejuni ST49#3 and ST52#4 outbreak cases, Denmark, July–October 2025","[{\"question\":\"What outbreaks were detected in Denmark during July–October 2025?\",\"answer\":\"Two concurrent Campylobacter jejuni outbreaks were identified: clones ST49#3 and ST52#4, detected through Denmark’s whole genome sequencing surveillance.\"},{\"question\":\"How severe were the two outbreaks clinically?\",\"answer\":\"Among infected individuals, 40% were hospitalized and 14% had bacteraemia, indicating clinically severe disease.\"},{\"question\":\"What was the suspected source of the outbreaks?\",\"answer\":\"Both outbreaks originated from Danish-produced chicken meat.\"}]","Increased severity of two concurrent Campylobacter jejuni clones causing large outbreaks, Denmark, July to October 2025 | PDF",1790776514,13]