Objective To analyze the epidemiological and clinical characteristics of the cases of human infection with avian influenza A (H9N2) virus and the contamination of H9 subtype avian influenza virus in the external environment in Hunan province during 2013−2022 and provide scientific evidence for the prevention and control of human infection with avian influenza A (H9N2) virus.

Methods The information about the cases of human infection with avian influenza A (H9N2) virus, including case reporting cards, field epidemic investigation and response reports, clinical and epidemiological characteristics of the cases, in Hunan from 2013 to 2022 were collected through the Infectious Disease Reporting Information Management System or the Public Health Emergency Reporting Management System of China Disease Prevention and Control Information System; From 2013 to 2022, external environmental samples were collected from urban and rural live poultry markets, large-scale poultry farms , poultry free range households, poultry slaughterhouses and processing factories and wild bird habitats in Hunan. Real time fluorescence quantitative polymerase chain reactionreaction (RT-PCR) was used to detect avian influenza virus in the samples, and statistical analysis was conducted by using the data of cases’ information and nucleic acid testing of avian influenza virus in external environmental samples.

Results From 2013 to 2022, a total of 14 cases of human infection with avian influenza A (H9N2) virus were reported in 11 counties or districts in 9 prefectures (municipality) of Hunan, all of which were sporadic mild cases and detected through routine monitoring of influenza like illness (ILI). Most cases were children, with a median age of 3.5 years (P₂₅=1.4, P₇₅=9.8). Thirteen cases developed fever, with a median highest body temperature of 39.0 ℃ (P₂₅=38.0, P₇₅=39.5); 57.00% of cases had exposures to poultry or live poultry markets, the processing, cooking, and slaughtering of poultry (8/14). From 2013 to 2022, a total of 39 225 external environment samples were collected from in Hunan. The positive rate of avian influenza A virus was 40.79% (15998/39225), and the H9 positive rate was 23.46% (9201/39225) in the external environment samples. The positive rate of subtype H9 virus showed an increasing trend year by year (Linear-by-Linear Association χ²=231.460, P<0.001). There were significant differences in subtype H9 virus positive rate among different surveillance sites (χ²=1 142.460, P<0.001), and the positive rate was highest in live poultry markets (26.28%); There were significant differences in subtype H9 virus positive rate among different types of samples (χ²=1 241.060, P<0.001). The highest positive rate (31.06%) was observed in samples of poultry cleaning water samples.

Conclusion The human infection with avian influenza A (H9N2) virus in was sporadic Hunan except some local areas. The contamination of subtype H9 virus in live poultry markets and poultry cleaning water was serious, and poultry and live poultry markets were the main sources of human infection with avian influenza virus. Therefore, it is necessary to improve the surveillance, prevention and control of avian influenza in population, strengthen the disinfection of poultry related external environment. Workers involved in the cooking and slaughtering of poultry should take effective personal protection.