Epidemiological and Genetic Characterization of Three H9N2 Viruses Causing Human Infections - Changsha City, Hunan Province, China, April 2025.

What is already known about this topic?: A total of 117 H9N2 cases of human infection of Chinese origin had been reported to the World Health Organization (WHO) by May 9, 2025, with 22 of them originating in Hunan Province. What is added by this report?: This article reported on the investigation of three new H9N2 avian influenza virus (AIV) infections detected in Changsha, Hunan Province, in April 2025. No epidemiological link was found among them. Exposure to live poultry was identified as the primary risk factor for infection. Sequence analysis of the three H9N2 AIVs showed a similarity of 99.71%-99.82% between hemagglutinin (HA), and the homology of the neuraminidase (NA) genes was 98.41%-99.83%. Although the tests showed that the HA had enhanced binding ability to upper respiratory tract cells' receptors, no evidence of sustained human-to-human transmission has been found so far. What are the implications for public health practice?: This study indicated that H9N2 AIV remains a public health issue in China. We need to strengthen publicity and education efforts to inform people of the potential risk of avian influenza virus, especially to keep children away from poultry and poultry-related facilities, to effectively prevent the occurrence of avian influenza A(H9N2) infection.