(P217) Low prevalence of asymptomatic Mpox virus in men attending sexual health services for HIV pre-exposure prophylaxis in England

Background: An outbreak of Monkeypox virus (Mpox) in individuals without travel links to endemic countries has been ongoing globally, since May 2022. Most of the 3543 cases in England (as of 21.11.22) have been in gay, bisexual and other men who have sex with men (GBMSM), presenting to sexual health services (SHS) with anogenital ulceration and a rash. Historically thought to cause only symptomatic infections, there have been reports of asymptomatic Mpox infections (1.34-6.5%) in GBMSM in two European studies during the current outbreak. We sought to identify whether there was evidence of asymptomatic infection in GBMSM in England.

Methods: Anonymised, residual clinical specimens from GBMSM undergoing routine screening as part of HIV PrEP care (01.08.22-07.10.22), were referred to the UK Health Security Agency, London, from three sexual health providers (two in London and one on the South-East coast). Specimens were pharyngeal (PS) and rectal swabs (RS) in NAATs buffer (various) and urine (neat/NAATs buffer). Triple-site specimens were requested but not available for all. DNA was extracted using the QIAsymphony DSP Virus/Pathogen Midi Kit (Qiagen) and used as template for a Mpox specific real-time PCR targeting the G2R_G gene, performed on the ABI 7500 or ViiA 7 (both Applied Biosystems) platforms.

Results: A total of 2917 clinical specimens (953/2917, 32.7% PS, 941/2917, 32.3% RS, 1023/2917, 35.1% urine) were received from 1158 GBMSM. Four specimens (4/2917, 0.14%) from two individuals (2/1158, 0.17%) tested positive for Mpox. Both attended the same London clinic. The first during the week of 8^th August was positive in the urine specimen only (PS and RS Mpox-negative). The second during the week of 19^th September tested positive at all three sites. The clinic confirmed that no participant was known to have symptomatic Mpox infection prior to or after specimen collection.

Conclusions: We report very low prevalence (0.17%) of asymptomatic Mpox infection suggesting that undetected infection is unlikely to be a main driver of ongoing transmission for high-risk GBMSM attending SHS in England. Further work is required to ascertain if infection is truly asymptomatic and, if so, the role this plays in transmission of infection.