Evaluation of Risk-Based Antigen and Antibody Surveillance Strategies and Their Association with HPAI Outbreaks in South Korean Duck FarmsRisk-Based Active Surveillance System Evaluation for Duck Farms in South Korea

Saleem AhmadDae Sung Yoo^*

• College of Veterinary Medicine, Chonnam National University, Gwangju, Republic of Korea

Highly pathogenic avian influenza (HPAI) continues to pose a serious threat to the poultry industry, emphasizing the importance of an effective surveillance system for early detection.This study evaluates the effectiveness of risk-based antigen and antibody surveillance strategies in South Korean duck farms by analyzing testing frequencies, testing intervals, and their association with HPAI outbreak occurrence.This study is the first to evaluate the HPAI serological surveillance system in South Korean duck farms, focusing on testing procedures and time intervals, along with their links to outbreak cases. Associations between HPAI outbreaks and antigen/antibody test frequencies were analyzed using spatial analytics and negative binomial regression. The results highlight differences in test frequencies between high-risk (October-May) and low-risk (June-September) periods, as well as between nonepidemic (2019-2020) and epidemic seasons (2020-2021 and 2021-2022). The findings indicate that antigen testing serves as an effective predictor of epidemics, particularly during high-risk periods (coefficient = 0.56, IRR: 1.75, p < 0.001). Hotspot analysis (Getis-Ord Gi, p < 0.001) revealed significant spatial clustering of outbreaks in relation to antigen testing intensity, indicating that cold spots received disproportionately more testing than hotspots and non-significant areas, highlighting a misalignment in risk-based surveillance prioritiesHot-spot analysis identified significant spatial clustering of outbreaks in relation to testing intensities (Getis-Ord Gi*, p < 0.01) and demonstrated the need for greater testing in cold spots relative to hot spots and non-significant Gi* categories. By assessing the duration between the last diagnostic test and the onset of HPAI outbreaks, this study also identified deficiencies in the surveillance system. No significant differences were observed in test-to-outbreak intervals