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