C05 | The butterfly effect – how a birthday party in Umbria led to the accidental discovery of a bi-regional outbreak of salmonellosis

F. Scoppetta¹, S. Magnanelli², S. Diomedi², E. Giannini³, R. Ortenzi⁴, A. Valiani⁴, L. Villa⁵, L. Barco⁶, M.A. Leo¹. | ¹Servizio Veterinario di Igiene degli Alimenti di Origine Animale IAOA, UslUmbria 2, Terni; ²Servizio Veterinario di Igiene degli Allevamenti e delle Produzioni Zootecniche IAPZ, UslUmbria 2, Terni; ³Servizio Igiene e Sanità Pubblica, UslUmbria 2, Terni; ⁴Unità Operativa Complessa Controllo Alimenti Umbria, Istituto Zooprofilattico Sperimentale dell'Umbria e delle Marche "Togo Rosati", Perugia; ⁵Dipartimento Malattie Infettive, Istituto Superiore di Sanità, Roma; ⁶Centro di referenza nazionale per le salmonellosi, Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro, Padova.

Purpose. The study describes an outbreak of salmonellosis involving 19 people between February and June 2025 in Umbria and Lazio, linked to the consumption of raw milk cheese produced by a farm dairy. Methods. The CU were carried out in accordance with the provisions of EU Regulation 2017/625, Art. 14. Four unrelated human cases of salmonellosis were reported, and an informal report was received of an additional case with gastrointestinal symptoms that occurred after a banquet at which cheese made from sheep's milk was consumed. The declarant did not formalise the report and did not indicate where the cheese had been purchased. Results. Salmonella Newport was typed from the strains isolated in the four initial cases; subsequently, five other human cases and a strain isolated from raw milk cheese from a private laboratory were added. A correlation between cheese consumption and human cases was therefore hypothesised. The private laboratory was contacted and provided the name of the same person who had made the informal report, who was then summoned to provide summary witness information, reporting the name of the producing dairy. The analyses carried out by the IZS involved showed that the sequenced strains belonged to a single cluster comprising the nine cases in Umbria and ten cases in the Lazio region. As a result, official samples were taken of “primo sale” raw milk cheese, mature pecorino cheese (> 30 days) and the water used; An official ban was imposed on all cheeses produced and cheese-making activities were suspended, with mandatory milk pasteurisation, requiring the OSA to carry out self-monitoring sampling of products, raw materials and surfaces. An epidemiological investigation was conducted on the farm: 172 samples of raw milk from lactating ewes, 172 rectal swabs, sampling of environmental surfaces using sponges, in particular on the milking machine, pools of fresh faeces, and sampling carried out with overshoes on sheep litter and in the poultry shed were collected. The following tested positive for Salmonella Newport: all samples of “primo sale” cheese, 50% of mature cheeses, raw bulk milk (intermittent positivity), a surface sample taken from a teat cup in the milking system, the overshoes used for sampling the poultry nests, and the milk of one of the lactating ewes. The OSA was notified of the offence pursuant to Article 444 of the Italian Criminal Code; the analytical results showed intermittent elimination of S. Newport by lactating animals and suggested poultry farming as the likely source of contamination. However, limited knowledge about the presence of Salmonella Newport in dairy sheep did not allow the source of milk contamination to be identified with certainty. Conclusions. This study highlights the importance of increasing controls and training for raw milk cheese producers, as well as strengthening the National Health Service networks for the management of foodborne diseases. It also highlights the need to raise consumer awareness of the importance of timely reporting as an essential tool for protecting public health.