Increased incidence of human West Nile and Usutu infections in Austria, 2024: analysis of data from 2009 to 2024

BACKGROUNDWest Nile virus (WNV) and Usutu virus (USUV) outbreaks in Europe pose growing public health concerns. In Austria, human WNV and USUV infections occur nearly every year since 2009 with notable case number variations.AIMWe analysed annual incidences and spatiotemporal distributions of human WNV and USUV infections in Austria in 2009-2024.METHODSAnnual incidence rates of laboratory-confirmed WNV and USUV cases recorded through the national surveillance were calculated, stratified by age, sex, clinical presentation, exposure place and virus sequence.RESULTSDuring 2009-2024, recorded case numbers were highest in 2024, with 37 WNV (19 male/18 female; median age: 62 years, range: 18-88) and 27 USUV infections (18 male/9 female; median age: 59 years, range: 20-69). Nineteen WNV cases developed West Nile neuroinvasive disease, while no USUV cases had neurological disease. Thirty-four of the WNV cases and all USUV cases were locally acquired. In northern Burgenland, an eastern Austrian region with an avian hotspot and only sporadic cases previously reported, WNV and USUV incidences respectively rose from averages of 0.6 and 1.0 per 100,000 in previous years to 6.6 and 4.2 per 100,000 in 2024. All 25 sequences analysed in 2024 from locally acquired WNV cases were of lineage 2. Among 15 USUV sequences, 14 belonged to the Europe-2 and one to the Africa-3 clade.CONCLUSIONHuman WNV and USUV infection increases in a previously low-incidence region underscore their increasing public health impact in Austria. Strengthening surveillance and response measures is essential for early detection, guiding prevention efforts, and ensuring blood donor safety.