CO39 | The FADOI-SIMIT Italian register of fever of unknown origins

V. Zerbato¹, L. Attard², A. Zanier³, M. Libanore⁴, A. Tedesco⁵, E. Pontali⁶, M. Campanini⁷, F. Dentali⁸, D. Manfellotto⁹, R. Luzzati¹ | ¹Unità di Malattie Infettive, ASUGI di Trieste, ²Unità di Malattie Infettive, IRCCS Policlinico S. Orsola, Bologna, ³Unità di Medicina Interna, OS Maria degli Angeli, Pordenone, ⁴Unità Operativa Complessa di Malattie Infettive, Azienda Ospedaliera Universitaria, Ferrara, ⁵Unità di Malattie Infettive e Tropicali e Microbiologia, IRCCS Sacro Cuore Don Calabria Hospital, Negrar di Valpolicella, Verona, ⁶Unità di Malattie Infettive, Ospedale Galliera, Genova, ⁷Unità di Medicina Interna, Ospedale Maggiore della Carità, Novara, ⁸Dipartimento Ricerca Centro Studi Fondazione FADOI, Milano; Dipartimento di Area Medica, Asst Sette Laghi, Varese, ⁹Dipartimento Ricerca Centro Studi Fondazione FADOI, Milano; Unità di Medicina Interna, Ospedale Isola Tiberina Gemelli, Roma, Italy

Background and Aims of the study: Fever of unknown origin (FUO) is a rare syndrome, but it has relevant morbidity, diagnostic complexity and high healthcare costs. From 20% to 50% of FUO cases remain with no diagnosis. Through a national register, a collaboration between the FADOI and SIMIT societies, this prospective study enrolled FUO cases observed in adult or hospitalized patients, or patients evaluated in 28 Italian centers (15 Infective Disease Units, and 13 Internal Medicine Units).
Materials and Methods: The fever (≥38.3°C) had to be found in more than one occasion and last >3 weeks, with no diagnosis after the first level exams. The register was active from 2019, October 1, to 2023, June 30. The study included a 6-month follow-up. We excluded HIV-positive, or neutropenic patients, or patients who were hospitalized for other pathologies. One hundred and eighty-seven patients were enrolled: 51% were women, with an average age of 54 (18-96 range); 40% with no comorbidities. Among the 177 patients who were ultimately evaluated, 28% received no diagnosis, 15% a possible diagnosis, and 57% a conclusive diagnosis. Causes include infections (38%), rheumatological (41%), neoplastic (14%), and other causes (7%). PET-CT was made on 65% of patients, leading to diagnosis in 41% of cases. A diagnosis was made after a median 23 days from enrollment; 65% of patients with a conclusive diagnosis had healed by the time of the follow-up.
Conclusions: This register gives an up-to-date insight of FUO causes, their evolution, and the diagnostic paths used in Italy.