Serological Response to Mpox and Direct Virus Detection in Asymptomatic Patient Prior to the First Diagnosed Case: A Retrospective Study of the 2022 Montpellier Epidemic.

The Mpox (formerly monkeypox) outbreak in 2022 presented unprecedented challenges, including widespread transmission in non-endemic regions, particularly among men who have sex with men. This study examines Mpox infections in Montpellier, France, focusing on diagnostic testing, serological profiles, and potential asymptomatic cases, based on data from Montpellier University Hospital. We retrospectively analyzed results from 91 patients tested positive for Mpox DNA. Antibody responses were monitored using novel Mpox virus peptide-based serological assays. Our findings highlight that MPXV antibodies can develop early in infection, peaking within 2 weeks to 3 months, though responses varied by antigen type. Additionally, asymptomatic Mpox infections were suggested, with virus detected in blood, urine, anal, oral and genital swabs screened Sexual Transmitted Infection samples. Notably, viral presence was confirmed in Montpellier samples as early as mid-May 2022, before the first known symptomatic case in Hospital, in the same period as the first official case in France. This study underscores the need for expanded screening in high-risk clinics to control Mpox spread and supports the potential utility of serological assays for broad immune profiling. Enhanced diagnostic tools and proactive surveillance in sexual health settings are recommended to improve outbreak response and prevent further transmission.