Diagnostic challenges in Flaviviridae infections: first human case of Usutu virus aseptic meningitis in an immunocompetent subject in Italy

OBJECTIVES: Usutu virus (USUV) is a mosquito-borne Orthoflavivirus. Human USUV infections are rare and are often asymptomatic or mild; however, neuroinvasive manifestations such as meningoencephalitis have occasionally been reported. DESIGN OR METHODS: Diagnosis of USUV infection is challenging due to serological cross-reactivity with other flaviviruses, particularly West Nile virus, which often shares the same geographical distribution, as well as the lack of rapid and accurate serological and molecular diagnostic tools. RESULTS: Here, we report the first case of aseptic meningitis caused by USUV in an immunocompetent subject in Italy. CONCLUSION: Highlighting the complex microbiological diagnostic pathway required to achieve an etiological diagnosis.