Dynamics of viral DNA shedding and culture viral DNA positivity in different clinical samples collected during the 2022 mpox outbreak in Lombardy, Italy

Background: Mpox virus (MPXV) has recently spread outside of sub-Saharan Africa. This large multicentre study was conducted in Lombardy, the most densely populated Italian region accounting for more than 40% of Italian cases. The present study aims to: i) evaluate the presence and the shedding duration of MPXV DNA in different body compartments correlating the MPXV viability with the time to onset of symptoms; ii) provide evidence of MPXV persistence in different body compartment as a source of infection and iii) characterize the MPXV evolution by whole genome sequencing (WGS) during the outbreak occurred in Italy. Material and methods: The study included 353 patients with a laboratory-confirmed diagnosis of MPXV infection screened in several clinical specimens in the period May 24th - September 1st, 2022. Viral isolation was attempted from different biological matrices and complete genome sequencing was performed for 61 MPXV strains. Results: MPXV DNA detection was more frequent in the skin (94.4%) with the longest median time of viral clearance (16 days). The actively-replicating virus in cell culture was obtained for 123/377 (32.6%) samples with a significant higher viral quantity on isolation positive samples (20 vs 31, p < 0.001). The phylogenetic analysis highlighted the high genetic identity of the MPXV strains collected, both globally and within the Lombardy region. Conclusion: Skin lesion is gold standard material and the high viral load and the actively-replicating virus observed in genital sites confirms that sexual contact plays a key role in the viral transmission.