Environmental surveillance of avian influenza viruses in Chongqing, China, 2020–2025

Background Avian influenza viruses (AIVs) pose animal and public health risks, but multi-year environmental surveillance data from Chongqing remain limited. Methods During 2020–2025, environmental samples, including chopping-board swabs, poultry fecal samples, cage-surface swabs, poultry-washing wastewater, and poultry drinking water, were collected from live poultry markets (LPMs), poultry slaughterhouses, commercial poultry farms, and backyard poultry operations in Chongqing, China. Influenza A virus RNA-positive samples were further tested for H5, H7, and H9. Detection rates were assessed by time, surveillance setting, sample type, and urban–rural stratum, and subtype-detection patterns were summarized among influenza A virus RNA-positive samples. Results Among 40,995 environmental samples, 17,725 were positive for influenza A virus RNA (43.24%). H9 had the highest detection rate among the three tested subtypes (32.30%), followed by H5 (12.71%); H7 had a detection rate of 0.09%. The annual influenza A virus RNA detection rate declined from 44.58% in 2020 to 39.01% in 2022 and rose to 49.46% in 2025; a test for trend in proportions indicated a significant overall upward trend during 2020–2025 ( P < 0.001). LPMs had the highest detection rates for influenza A virus RNA (48.89%), H5 (15.39%), and H9 (35.89%). Among influenza A virus RNA-positive samples, H9-only detection was most frequent (55.61%), followed by H5/H9 co-detection (19.02%), which reached its highest observed annual proportion in 2025 (24.56%). Conclusions Environmental surveillance demonstrated sustained AIV RNA detection in poultry-associated environments in Chongqing. H9 was the most frequently detected of the three tested subtypes, H5 was detected in every study year, and LPMs had the highest influenza A virus RNA detection rate among surveillance settings.