Prevalence of Mpox (Monkeypox) in patients undergoing STI screening in northern California, April-September 2022.

BACKGROUND: Despite the sharp increase in mpox (formerly monkeypox) incidence and the wide geographic spread of mpox during the 2022 outbreak, the community prevalence of infection remains poorly characterized. This study is a retrospective epidemiologic survey to estimate mpox prevalence. METHODS: Samples obtained for sexually transmitted infection (STI) testing from April to September 2022 in the public hospital and clinic system of San Mateo County, California were screened for mpox virus (MPXV) using polymerase chain reaction. RESULTS: 16/1,848 samples from 11/1,645 individuals were positive for MPXV by qPCR. 4/11 individuals with positive MPXV testing were cisgender women, 2 of whom were pregnant at the time of sample collection. Both deliveries were complicated by chorioamnionitis. Anorectal and oropharyngeal samples were the most likely to be positive for MPXV (4/60 anorectal samples and 4/66 oropharyngeal samples compared with 5/1,264 urine samples and 3/445 vaginal samples). CONCLUSIONS: Our study is one of the first epidemiologic surveys for MPXV infection outside of sexual health/STI clinic settings. Relatively high rates of MPXV from oropharyngeal and anorectal samples reinforces the importance of MPXV testing at various anatomic sites, particularly if patients are presenting with non-lesional symptoms (pharyngitis, proctitis). However, the United States Food and Drug Administration (FDA) has not yet authorized non-lesional MPXV testing. The identification of MPXV in women in our cohort suggests that the rates of mpox in women may have previously been underestimated and highlights the risk of pregnancy complications associated with mpox.