Announcement

**Pathfinder** · August 14, 2025, 08:31 AM

Extensive cryptic circulation sustains mpox among men who have sex with men

Posted August 13, 2025.

Joseph Lewnard, Miguel I Paredes, Matan Yechezkel, Gregg S Davis, Vennis Hong, Jessica Skela, Utsav Pandey, Noah T Parker, Lauren C Granskog, Magdalena E Pomichowski, Iris Anne C Reyes, Isabel Rodriguez Barraquer, Nicola F Mueller, Sara Y Tartof
doi: https://doi.org/10.1101/2025.08.09.25333368

This article is a preprint and has not been certified by peer review [what does this mean?]. It reports new medical research that has yet to be evaluated and so should not be used to guide clinical practice.

Abstract

Sporadic cases of mpox continue among men who have sex with men (MSM), with most lacking identifiable transmission links. To resolve underlying dynamics, we prospectively tested for monkeypox virus (MPXV) in rectal swabs from MSM in Los Angeles during summer, 2024, finding that infections exceeded reported mpox cases 33-fold (95% confidence interval: 16-68). Accounting for under-reporting, incidence rates of MPXV infection were comparable to Neisseria gonorrhoeae and Chlamydia trachomatis among MSM. Independent estimates derived from MPXV phylogenetic reconstruction and a meta-analysis of surveillance studies corroborated this extensive under-reporting. We estimate that undiagnosed infections must cause at least 31-44% of all transmission to explain observed MPXV phylogenies; under realistic modeling assumptions, this proportion rises to 61-94%. Contrary to current guidance, our findings suggest MPXV is prevalent among MSM, predominantly causes subclinical infection, and is sustained in circulation by cryptic transmission.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

This work was funded by the Center for Forecasting and Outbreak Analytics of the US Centers for Disease Control & Prevention via the Insight Net cooperative agreement (CDC-RFA-FT-23-0069 to SYT and JAL). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention.

...

Extensive cryptic circulation sustains mpox among men who have sex with men

https://www.medrxiv.org/content/10.1101/2025.08.09.25333368v1

Sporadic cases of mpox continue among men who have sex with men (MSM), with most lacking identifiable transmission links. To resolve underlying dynamics, we prospectively tested for monkeypox virus (MPXV) in rectal swabs from MSM in Los Angeles during summer, 2024, finding that infections exceeded reported mpox cases 33-fold (95% confidence interval: 16-68). Accounting for under-reporting, incidence rates of MPXV infection were comparable to Neisseria gonorrhoeae and Chlamydia trachomatis among MSM. Independent estimates derived from MPXV phylogenetic reconstruction and a meta-analysis of surveillance studies corroborated this extensive under-reporting. We estimate that undiagnosed infections must cause at least 31-44% of all transmission to explain observed MPXV phylogenies; under realistic modeling assumptions, this proportion rises to 61-94%. Contrary to current guidance, our findings suggest MPXV is prevalent among MSM, predominantly causes subclinical infection, and is sustained in circulation by cryptic transmission. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was funded by the Center for Forecasting and Outbreak Analytics of the US Centers for Disease Control & Prevention via the Insight Net cooperative agreement (CDC-RFA-FT-23-0069 to SYT and JAL). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Kaiser Permanente Southern California Institutional Review Board approved this study with a waiver of informed consent for analysis of remnant specimens and patient electronic health records. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Individuals wishing to access study data must enter into a data access agreement with Kaiser Permanente Southern California.

Announcement

CA: Mpox cases rising in LA County

CA: Mpox cases rising in LA County

Comment