Objective: To evaluate the prevalence and characteristics of concurrent bacterial sexually transmitted infections (bSTIs) among individuals with mpox. Design: Prospective cohort study of participants aged 18 years or older with confirmed mpox conducted in Rio de Janeiro, Brazil. This cross-sectional analysis include only participants who underwent bSTI testing at baseline between June 2022 and January 2024. Methods: Participants were offered testing for chlamydia/gonorrhea (NAAT, anorectal swabs) and syphilis (active diagnosis if VDRL ≥ 1/8). Baseline prevalence of bSTIs was calculated, and participant characteristics were described based on bSTI diagnosis (yes/no). Chi-squared/Fisher's tests were used for qualitative variables, and the Wilcoxon rank-sum test for quantitative variables. Results: Out of 634 enrolled participants, 538 (84.9%) were tested for STIs and included in this analysis, mostly cisgender men, aged 30–39 years with post-secondary education. Overall prevalence of concurrent bSTI was 37.3%, mainly syphilis, followed by chlamydia and gonorrhea. Half of the participants had HIV coinfection, and one-third were on PrEP. Concurrent bSTI diagnosis at the time of mpox assessment was associated with being aged 30–39 years, self-identifying as cisgender men, having HIV-positive status, reporting proctitis symptoms and reporting any STI in the past 12 months. Conclusions: Our data reveals a notable prevalence of concurrent STIs among participants with confirmed mpox at a prominent infectious diseases’ referral center in Rio de Janeiro, Brazil. These findings underscore the importance of integrating mpox into the differential diagnosis of anogenital manifestations and to promote combination prevention strategies within sexual health care services.

Mpox, sexually transmitted infections and combination prevention: insights from a major cohort in Rio de Janeiro, Brazil