P33 | Salmonella Newport: genomic analysis of an outbreak linked to the consumption of raw sheep's milk products

C. Licciardi¹, S. Primavilla¹ L. Barco², G. Baggio², L. Villa³, I. Artuso³, C. Lucarelli³, F. Scoppetta⁴, M.A. Leo⁴, M.L. De Marchis⁵, T. Bossù⁵, A. Valiani¹, R. Ortenzi¹. | ¹ Istituto Zooprofilattico Sperimentale dell’Umbria e delle Marche “Togo Rosati” IZSUM; ² Centro di referenza nazionale per le salmonellosi - Istituto Zooprofilattico Sperimentale delle Venezie; ³ Dipartimento di Malattie Infettive, Istituto Superiore di Sanità ISS; ⁴Servizio di Igiene Alimenti Origine Animale, USL Umbria2; ⁵Istituto Zooprofilattico Sperimentale del Lazio e della Toscana, Italy

Purpose. Salmonella spp. infection is the second most reported zoonosis in humans in Europe and is responsible for foodborne outbreaks (in 2023, cases increased by 16.9% compared to 2022, according to EFSA). To combat its spread, it is important to use a One Health approach, employing surveillance systems that ensure its control. The aim of this study was to describe an outbreak of S. Newport that affected 9 people in Umbria and 10 in Lazio between February and April 2025. The epidemiological investigation was coordinated by the Local Competent Authority (LCA) in the areas where raw sheep's milk cheese consumption had occurred, identified as the probable cause of the outbreak. Methods. Since the beginning of the year, an increase in human-origin Salmonella strains belonging to serotype Newport has been observed at the IZSUM in Perugia (CRRPE) and at the IZSLT in Rome (CREP/LRPTAU). Additionally, a private regional laboratory has provided the CRRPE with an S. Newport isolate from cheese. The presence of the strain isolated from the food matrix allowed us to hypothesize a correlation between human cases and the food. Following the epidemiological investigation conducted by the ACL, it was possible to trace the cheese factory where the cheese was produced. Targeted sampling was carried out, collecting milk and cheese samples. Samples of pooled feces and mammary secretions were then taken within the farm attached to the dairy, as well as environmental swabs in the milking area. The microbiological analysis of the samples was carried out by the Perugia Food Control Laboratory of the IZSUM using a validated alternative method (AFNOR BIO 12/16-09/05). Samples that tested positive in the screening were confirmed in accordance with ISO 6579-1:2017. The isolated Salmonella spp. strains were subjected to rapid serotyping (ISO/TR 6579-3:2014). All human isolates and those derived from samples taken at the farm/dairy were subjected to Whole Genome Sequencing (WGS). Genomic analyzes were conducted by the Enter-Net Italy Surveillance Coordination (ISS) and the National Reference Center for Salmonellosis. cgMLST analysis was performed on genomes assembled using the chewBBACA 2.8.5 program, with the INNUENDO scheme. Results. Microbiological analyzes revealed the presence of S. Newport in the cheeses, raw milk samples, and environmental samples. WGS analyzes revealed that the human-origin strains and those isolated on the farm belong to the same cluster with a distance of 0-2 Allele Distance (AD). The identified cluster consists of 19 isolates (10 from Lazio and 9 from Umbria) of human origin, 1 from raw milk cheese submitted by a private laboratory, and 5 isolates from samples taken on the farm. Genomic analyzes indicate a close correlation between the consumption of fresh raw sheep's milk cheese "primo sale" and the recorded human cases. Conclusions. Despite the challenges encountered in building networks for the management of foodborne illnesses, the results reported in this study indicate that the key factor in managing toxic infections is intersectoral collaboration between peripheral human medicine laboratories, the IZSLSs, the ISS, and the Competent Authorities at the national, regional, and local levels.