Meningiti, meningo-encefaliti ed encefaliti da virus Toscana in Italia, 2016-2021. Punta dell’iceberg di una arbovirosi endemica poco conosciuta

Toscana virus meningitis, meningo-encephalitis and encephalitis in Italy, 2016-2021: the tip of the iceberg of a poorly known endemic arbovirus Introduction Toscana virus (TOSV) is an emerging pathogen, however it is seldom considered by physicians among the differential diagnoses of summer meningitis, leading to under-ascertainment. The aim of this study is to describe cases of laboratory confirmed TOSV central nervous system (CNS) infections, notified in Italy in the period 2016-2021. Materials and methods We described all cases of meningitis/meningo-encephalitis/encephalitis notified to the Italian national TOSV surveillance system from 2016 to 2021. All cases were laboratory-confirmed. We calculated incidence (overall, stratified by year, sex, age group and by municipal urbanization level) and the frequency of hospitalizations and deaths. Results Between June 2016 and October 2021, 331 confirmed cases of TOSV meningitis/meningo-encephalitis/ encephalitis were reported in Italy (median 56 cases/year) of whom 292 were hospitalized. The cases were reported in 9/21 Italian Regions with the highest incidence in rural municipalities. Average age was 46 (range 0-89 years), most cases were male (233, 70%). An increased notification rate was observed in 2018 when incidence (1.47 cases/1,000,000) was almost twice the mean incidence in the remaining study period (0.81 cases/1,000,000). Overall, incidence was higher in age groups between 20 and 59 years. In 2020-2021 no deaths were reported. Discussion and conclusions The number of human infections caused by TOSV in Italy is under-estimated and diverse testing policies may bias the observed case distribution. Higher incidences in working age males and in rural municipalities might point to specific risk factors, also occupational. While no deaths were recently reported, TOSV impacts on hospital services.