Usutu virus infections in humans: a retrospective analysis in the municipality of Modena, Italy

Objective To monitor the spread and to evaluate the role for public health of Usutu virus (USUV) in an endemic area of Italy. Methods The survey was retrospectively conducted by detecting USUV RNA and USUV antibodies in cerebrospinal fluid and serum samples collected between 2008 and 2011 from 915 patients with or without neurologic impairments in the area of the municipality of Modena, Italy. Organs of birds and pools of mosquitoes were also tested for USUV RNA. Positive samples were partially sequenced and used for phylogenetic analysis. Results The presence of USUV RNA (1.1%; 95% confidence interval (CI) 0.6–2.0) was significantly (p <0.05) higher than that of West Nile virus (0%; 95% CI 0–0.33). USUV antibody level was 6.57% (95% CI 4.87–8.82), and it was significantly higher (p <0.05) compared to that of West Nile virus (p 2.96, 95% CI 1.89–4.62). Partial genome sequencing of USUV strains detected in humans, birds and mosquitoes revealed high nucleotide sequence identity within them and with the USUV strains isolated in Central Europe. Conclusions USUV infection in humans is not a sporadic event in the studied area, and USUV neuroinvasiveness has been confirmed.