Prevalence and characterization of West Nile virus infections among people living with HIV in Northern Italy: a sero-repository analysis

BACKGROUND: West Nile virus (WNV) is increasingly reported in Italy, yet its population prevalence remains uncertain. People living with HIV (PLWH) may be at increased risk of WNV severe manifestations, including neuroinvasive disease. This study assessed the seroprevalence and factors associated with WNV seropositivity among PLWH in a large Northern Italian cohort. METHODS: This retrospective single-center study included all PLWH followed at the Brescia HIV Outpatient Clinic with at least one serum sample collected in 2022 and stored in the institutional sero-repository. Samples were screened for WNV antibodies using ELISA; reactive or borderline samples were confirmed by immunofluorescence assay for IgG and IgM and further characterized by microneutralization assays to differentiate WNV from USUV infection. Associations with seropositivity were evaluated using univariate logistic regression. RESULTS: Among 2,843 PLWH, 76.2% were male, the mean age was 54.1 (± 10.5), and 87.2% were of Italian origin. Most participants had virologically suppressed HIV infection and were receiving stable antiretroviral therapy (94.2%). WNV serological screening by ELISA identified IgG positivity in 176 participants (6.2%). Of these, 166 tested positive by immunofluorescence assay. Neutralization assays subsequently confirmed WNV seropositivity in 86 participants (3.0%), USUV seropositivity in 12 (0.6%), and dual WNV/USUV neutralizing antibody positivity in 6 (0.2%). No neuroinvasive diseases were reported. Compared with seronegative individuals, seropositive participants were less frequently male (p = 0.001), younger (p < 0.001) and differed significantly by geographic origin (p < 0.001), with a higher prevalence among PLWH born outside Europe. In logistic regression analyses, geographic origin was strongly associated with seropositivity: participants from Africa (OR 21.22, 95% CI 12.49-36.03), Asia (OR = 23.31, 95% CI: 10.19-53.31), and the Americas (OR 19.16, 95% CI 9.45-38.83) had markedly higher odds compared with participants of Italian origin (all p < 0.001). DISCUSSION: This is, to our knowledge, the first study evaluating WNV seroprevalence among PLWH. Seroprevalence was higher than that reported in comparable European blood donor populations. In this largely virologically suppressed, stably treated outpatient cohort, no severe manifestations were observed and symptoms were infrequently recalled.