The Istituto Superiore di Sanità published the Report no. 8 on West Nile virus surveillancewith data updated to September 16, 2026. Since the beginning of the surveillance season they are 657 confirmed cases of infection in humans, compared to 594 in the previous report. The RNA virus of the Flaviviridae family is transmitted through mosquito bite of this kind Culexand not from person to person: the natural reservoir is the birdswhile humans and horses are occasional guests. As reported by the Istituto Superiore di Sanità, in most cases the infection is asymptomatic; among symptomatic cases, approximately 20% develop mild, flu-like symptoms such as fever, headache, nausea and muscle pain, while less than1% goes towards neurological complications. The bulletin is released every week and the data for the last four weeks are considered not yet consolidated, therefore subject to possible revisions.
The toll of WNV infections in 2026
Of the 657 cases confirmed as of September 16, the ISS distinguishes different clinical forms:
- 345 cases in neuro-invasive formthe most serious manifestation, in which the infection affects the nervous system. Of these, 5 are cases imported by those returning from a trip abroad (1 Maldives, 1 France, 1 Belgium, 1 Greece, 1 Holland).
- 224 cases of fever (of which 1 imported from Burkina Faso).
- 80 asymptomatic cases identified among blood donors, intercepted thanks to donation controls.
- 4 cases with other symptoms And 4 asymptomatic cases.
The spread on Italian territory: affected regions and provinces
They go up to 82 Provinces with demonstrated circulation of the virusbelonging to 19 Regions: Piedmont, Valle d’Aosta, Lombardy, PA of Trento, Veneto, Friuli-Venezia Giulia, Liguria, Emilia-Romagna, Tuscany, Umbria, Marche, Lazio, Abruzzo, Molise, Campania, Puglia, Calabria, Sicily and Sardinia. In the previous report (data as of 9 September) there were 79 provinces.
The demonstrated circulation does not only concern human cases, but also the detection of the virus in mosquitoes, birds And horses. In terms of human cases, the regions with the highest numbers are the Lombardy (158 cases), the Veneto (116), the Lazio (96) and the Piedmont (87), followed by Emilia-Romagna (66), Campania (39), Sardinia (28) e Tuscany (25). Among the individual provinces, the most affected are Rome, Padua and Milan.
Deaths and data on clinical lethality: ISS data
Among the confirmed cases have been notified 51 deathsone of them in one imported case. The ISS calculates the lethality not on the total number of infections, but only on the reported and confirmed autochthonous neuro-invasive forms: on this basis it is equal to 14.7%. In the same period of 2025 the value was 15.8%therefore slightly decreasing. Since these are data not yet consolidated for the most recent weeks, the value should be considered provisional.
In the same period the bulletin reports 14 cases of Usutu virusa Flavivirus transmitted by the same Culex mosquitoes and monitored in parallel to West Nile. The cases are distributed as follows: 8 in Lombardy, 2 in Lazio, and 1 each in Emilia-Romagna, Marche, Piedmont and Veneto.
