Three-Phase Decline in Reported Farm-Level Fowl Typhoid Occurrence in the Republic of Korea, 2000–2024: Temporal Alignment with the 2016–2017 H5N6 HPAI Epidemic

Abstract

Simple Summary Fowl typhoid is a serious bacterial disease of chickens that can cause high mortality and substantial economic losses. This study examined 1495 national farm-level notifications in the Republic of Korea from 2000 to 2024 to determine how the long-term reported trend changed over time. Formal model comparison using the Bayesian information criterion favored a pattern with two changes in slope, defining an initial decline from 2000 to 2009, a period of little overall change from 2009 to 2016, and a faster decline after 2016. The final phase overlapped in time with the large 2016–2017 H5N6 highly pathogenic avian influenza epidemic. However, provinces with more avian influenza outbreaks did not consistently show faster reductions in fowl typhoid. Because this study did not directly measure biosecurity intensity, vaccination coverage, surveillance effort, or changes in the poultry population and industry structure, it cannot identify the mechanism responsible for the post-2016 decline. The results therefore describe a long-term pattern in reported farm-level notifications and a temporal overlap with the HPAI epidemic period, rather than a causal effect of HPAI control measures.