Objectives To analyze the epidemiological and clinical characteristics of human cases of H9N2 avian influenza in Hunan Province, 2013 - 2022, as well as the pollution of the H9 subtype avian influenza virus in the external environment, to provide scientific basis for the prevention and control of human infection with H9N2 avian influenza.

Methods From 2013 to 2022, human infection with H9N2 avian influenza in Hunan Province , case report cards, and on-site investigation and disposal reports of the epidemic, clinical and epidemiological information of the cases were collected through the Infectious Disease Reporting Information Management System or the Emergency Public Health Event Reporting Management System of the China Disease Prevention and Control Information System ; From 2013 to 2022, 39225 external environmental samples were collected from 5 types of places in Hunan, including urban and rural live poultry markets, large-scale breeding farms (households), poultry free range households, poultry slaughterhouses and processing factories, and wild bird habitats. Real time fluorescence quantitative analysis (RT-PCR) was used to detect avian influenza virus in the samples, and statistical analysis was conducted on 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 H9N2 avian influenza were reported in Hunan Province, all of which were sporadic mild cases and were detected through routine monitoring of influenza like cases (ILI). The main cases are children, with a median age of 3.5 years（P25=1.4, P75=9.8）, involving 11 counties and districts in 9 cities and prefectures of Hunan Province; 13 cases developed fever, with a median highest body temperature of 39.0 ℃（P25=38.0, P75=39.5）; 57.00% of cases had a history of exposure to poultry or live poultry markets, processing, cooking, and slaughter (8/14). From 2013 to 2022, a total of 39225 samples of avian influenza were collected from external environments for disease detection in Hunan Province. The positive rate of Type A avian influenza virus was 40.79% (15998/39225), of which the H9 positive rate was 23.46% (9201/39225). The H9 positive rate shows an increasing trend year by year（Linear-by-Linear Association χ2 =231.46，P < 0.001）。There was significant difference in H9 positive rate among different surveillance sites (χ2 = 1 142.46, P < 0.001), and H9 positive rate was the highest in live poultry market (26.28%); There was significant difference in H9 positive rate among different types of samples (χ2 = 1 241. 06, P < 0.001) .The highest H9 positivity rate (31.06%) was observed in samples of poultry wastewater during cleaning.

Conclusion The human infection with H9N2 avian influenza in Hunan Province is sporadic throughout the province, with some areas being more concentrated. The H9 subtype pollution in live poultry trading markets and poultry wastewater is severe, and poultry and live poultry markets are the main sources of human infection with avian influenza virus. Therefore, it is necessary to monitor and prevent avian influenza in the population and external environment, strengthen the disinfection of the external environment in various bird related places, and workers involved in the cooking and slaughtering of poultry should take personal protection.