Serological evidence supports the transmission of clade Ib mpox virus by professional sex workers and spread within households in South Kivu, DRC

Understanding secondary attack rates is a key knowledge gap in the ongoing clade Ib mpox virus (MPXV) outbreak in the Democratic Republic of the Congo. Here, we report the first serological study to investigate the extent of local MPXV clade Ib transmission, performed in South Kivu, DRC. Sera were collected in November and December 2023 (n=120), and May 2024 (n=48) from professional sex workers (PSW) and visitors of 25 bars with reports of mpox cases. In 18% and 17% of these sera, respectively, serological evidence for MPXV infection was detected, indicating that PSW played an important role in MPXV clade Ib transmission in this region. Additionally, sera from 108 direct contacts of mpox cases from 34 households were collected between September 2023 and May 2024. At least one serum sample tested seropositive in 50% of households. Serological studies are needed to comprehend the extent and severity of the ongoing MPXV outbreak, and may be used to guide targeted vaccination strategies, particularly for high-risk groups.