Abstract:Objective To investigate the discovery and disposal process and epidemiological characteristics of the first confirmed case of mpox (formerly named monkeypox) in Huai’an, Jiangsu Province, and to provide reference for the prevention and control of key infectious diseases in this region. Methods The on-site epidemiological investigation data of the first confirmed case of mpox on June 21, 2023, as well as the results of nucleic acid detection and gene sequencing of laboratory specimens were analyzed retrospectively. Possible sources of infection were explored. Results The first confirmed case of mpox was an AIDS patient, men who had sex with men (MSM), who had no history of travel abroad or outside the city within 21 days before the onset of the disease, but had interacted with some people outside the city, and the epidemiological trajectory was complex. The detection of mpox virus nucleic acid was positive (BioGerm reagent: Ct value 21.8, ZhuoCheng reagent: Ct value 21.2). According to genetic sequencing, the first confirmed case was classified as C.1.1 lineage of clade IIb. During the investigation on the source of infection of the first confirmed case, one new asymptomatic infected person was found. Based on the epidemiological investigation and laboratory results, the first confirmed case was believed to be caused by local infection, however, the source of infection was unclear. Although there was an epidemiological association with asymptomatic infected people, the direct evidence of mutual infection was insufficient, and it could not be ruled out that there was still a hidden transmission chain between regions. The source of infection of the asymptomatic infected person was presumed to be the first confirmed case or an unidentified person with whom he had high-risk sex and caused anal bleeding. Conclusion The first confirmed case is caused by local infection. Awareness of case diagnosis and reporting in medical institutions should be improved, and publicity and education should be provided to key exposed populations, especially those men who have sex with men, to prevent the occurrence of large-scale local epidemic.