Characteristics of the first confirmed case of human infection with mpox virus clade Ib in China.

Mpox clade Ib is significant as it is associated with human cases and plays a key role in understanding the transmission and public health implications of mpox outbreaks. Here we present a case report of the first confirmed human infection of clade Ib in China, which occurred in December 2025 in Zhejiang Province. The case was a 28-year-old woman from South Africa who had sexual contact with an asymptomatic man from the Democratic Republic of the Congo. She presented with disseminated vesicular lesions on the extremities, face, buttocks, trunk, palms, and dorsum of the hands, but lesions were absent from the oral cavity, perineum, and anus. By the 18th day post-onset (DPO), only vesicles remained on the dorsum of the right foot and in the finger web spaces, with complete resolution by the 24th DPO. Among 59 consecutive samples collected, 55 tested positive for mpox virus. Oropharyngeal swabs turned negative by the 16th DPO, while skin lesion samples, urine samples, and scab specimens remained positive through the 20th DPO. Consecutive scab samples consistently exhibited high viral loads. In total, 211 contacts of the symptomatic patient were identified, and no secondary cases occurred. This study underscores the importance of multisite sampling for diagnostic sensitivity, highlights the transmission risk associated with asymptomatic sexual contact, and emphasizes the need for refined contact definitions and management strategies. Further research is needed to explore infection risks across different types of exposure.