Viral loads in clinical samples of men with monkeypox virus infection: a French case series

Background: Monkeypox virus (MPXV) is currently spreading among men who have sex with men, outside of sub-Saharan Africa, and close contact during sex seems to be one of the key pathways of viral transmission in the current outbreak. Our aim was to describe the distribution of MPXV in the human body, as it might play a role in its dissemination through sexual contact.Methods: The study population in this case series consisted of patients with confirmed MPXV infection attending the Pitié-Salpêtrière Hospital (Paris, France), who had been sampled from multiple anatomical sites, including skin, anus, throat, blood, urine, and semen, at diagnosis and 2 weeks later. We compared the proportion of positive samples and MPXV viral loads (given as PCR cycle thresholds [Ct]) between anatomical sites, and between day 0 (D0) and D14.Findings: Overall, 356 samples were collected between May 20 and June 13, 2022, from 50 men with a median age of 34 years (IQR 29-40). 22 (44%) of the 50 men were classified as HIV-negative on day (D)0, and 22 (44%) were living with HIV. At D0, MPXV detection was more frequent from skin (44 [88%] of 50), anus (30 [71%] of 42), and throat (36 [77%] of 47) than from blood (13 [29%] of 45), urine (nine [22%] of 41), or semen (13 [54%] of 24). Viral loads were significantly higher from skin lesions (Ct 19·8) and anal samples (Ct 20·9) than from throat (Ct 27·2), blood (Ct 32·8), urine (31·1), or semen samples (Ct 27·8). When analysing the 107 samples taken from 24 patients at D14, the proportion of positive samples strongly decreased between D0 and D14 at all sites: skin (four [22%] of 18), anus (two [9%] of 22), throat (none of 21), blood (one [5%] of 21), urine (none of 14), and semen (two [9%] of 11).Interpretation: These data contribute to a better understanding of how the virus might spread between sexual partners over a relatively short period of time. High MPXV viral loads from skin and mucosa, including genital and anal sites, suggest that transmission most likely occurs through direct body contact rather than through the respiratory route or contact with body fluids, which should help to refine the prevention messages delivered to individuals most exposed to the virus.