Clinical, epidemiological, and virological features of Mpox in Beijing, China - May 31-June 21, 2023

The first locally acquired case in the Chinese mainland was reported on May 31, 2023, lagging behind other countries. In this study, we aimed to examine the early clinical and epidemiological characteristics of the earliest cases of Mpox in Beijing, China. Additionally, we investigated the sequence and transmission patterns of the Mpox virus (MPXV). We analyzed 37 reported cases of Mpox in Beijing from May 31, 2023 to June 21, 2023. The age range of the subjects was 24-51 years. Thirty-six cases (97.3%) were identified in men who have sex with men (MSM), and 19 cases (51.4%) tested positive for the human immunodeficiency virus. Thirty-three cases were symptomatic, while four were asymptomatic. Skin lesions were observed in 32 cases (97.0%), fever in 26 (78.8%), and swollen lymph nodes in 17 (51.5%). Rash typically appeared in the genital or perianal area 1-3 days before fever onset, with a minimum incubation period of 2 days. For individuals with skin rashes, the skin lesion samples showed 100% positivity and low Ct values. There were high oropharyngeal swab (75.8%) and blood (84.6%) positivity rates. All MPXV strains belonged to the B.1.3 branch of the West African lineage. These strains carried 76-86 nucleotide substitutions compared with the reference human MPXV genome, and genetic diversity was observed. Our findings provide the first insights into the landscape of early transmission of Mpox in Beijing and help inform policy formulation in the Chinese mainland.