2018–2025 Serological study on avian influenza among occupationally exposed populations in the Poyang Lake area — the region with the highest environmental surveillance positive rate in China

An avian influenza virus positivity rate as high as 82.3% has been reported in Jiangxi Province, China, underscoring this region as a potential hotspot for avian influenza virus circulation. As a crucial hub for migratory birds and a region where wild birds, domestic poultry, and humans frequently overlap, Poyang Lake provides favorable ecological conditions for cross-species transmission of avian influenza viruses. This study aimed to describe the seroprevalence of antibodies against selected avian influenza virus subtypes among occupationally exposed populations at surveillance sites around Poyang Lake from 2018 to 2025, and to provide data to inform ongoing surveillance and risk assessment. A cross-sectional serological surveillance was conducted annually during winter and spring from 2018 to 2025 in Nanchang County (Nanchang) and Duchang and Wuning Counties (Jiujiang), Jiangxi Province. Serum samples were collected from occupationally exposed individuals, including backyard poultry keepers and their household members and live poultry market workers with direct poultry contact. Hemagglutination inhibition assays were performed by the National Influenza Center to assess antibody reactivity against the test antigens representing H5N6, H9N2, H7N9, H3N8, H10N3, H5N8, and H5N1. Predefined HI positivity thresholds were ≥ 1:20 for H3N8, H5N8, H5N1, H7N9, and H10N3 and ≥ 1:40 for H5N6 and H9N2. A total of 2,437 valid serum samples were analyzed (1,599 from Jiujiang and 838 from Nanchang). Overall, 108 samples (4.43%) met the predefined HI positivity threshold for H5N6, and 107 (4.39%) met the threshold for H9N2. During 2018–2020, 25 of 914 samples (2.74%) met the threshold for H7N9. During 2021–2025, 22 of 1,523 samples (1.44%) met the threshold for H3N8, including 9 of 100 samples (9.00%) collected in Nanchang in the 2024 surveillance year. Four of 1,523 samples (0.26%) met the threshold for H10N3; all four were from Jiujiang in the 2024 surveillance year. Four of 314 samples (1.27%) met the threshold for H5N8 in 2020. None of the 600 samples tested for H5N1 in the 2024 and 2025 surveillance years met the predefined threshold. HI antibody reactivity varied across subtypes, surveillance locations, and years among occupationally exposed participants around Poyang Lake. The H3N8 finding in Nanchang and the H10N3 finding in Jiujiang in the 2024 surveillance year warrant further investigation. H5N6 peaks in Jiujiang in 2021 and in Nanchang in 2022; H9N2 peaks in 2021 in Jiujiang and 2023 in Nanchang. HI reactivity alone does not establish subtype-specific human infection or local virus circulation. Continued serological surveillance, interpreted alongside poultry and environmental virological data, may inform risk assessment.