Enterotoxigenic Escherichia coli (ETEC) and Clostridium perfringens are key pathogens responsible for neonatal and post-weaning diarrhea, causing notable morbidity, mortality, and economic loss worldwide. However, nationwide data on bacterial pathogens causing piglet diarrhea in Korea remain limited. This study aimed to determine the prevalence and distribution of E. coli fimbrial and toxin genes, C. perfringens, and Clostridioides difficile in diarrheic piglets in Korea (2023-2024). Overall, 1,339 fecal samples were collected from diarrheic piglets across Korean pig farms. Species-specific virulence genes were detected using real-time polymerase chain reaction assay targeting major fimbrial and toxin factors of E. coli, C. perfringens (CPA), and C. difficile (TcdA/TcdB). Prevalence was compared across years and seasons. Among E. coli fimbrial factors, F18 (17.0%), F4 (7.4%), and F17 (4.7%) were common, whereas F5, F6, and F41 were rare (<3%). STb (30.1%) and STa (21.1%) were common, and Stx2e prevalence increased from 6.8% to 13.4% (p < 0.001). LT was detected in 9.0% of cases; C. perfringens in 22.3% of cases, increasing from 17.9% to 27.4% (p < 0.001); and C. difficile in 7.7% of cases. Several pathogens showed quarterly variations, with F4 and STa peaking in Q1 (January-March), STb in Q3 (July-September), and C. perfringens showing higher detection rates in Q1 and Q4 (October-December). ETEC-associated fimbrial and toxin genes, particularly F18/F4 and STa/STb, remained the most frequently detected among diarrheic piglets in Korea, with Stx2e and C. perfringens also playing important roles. These findings highlight the multifactorial nature of piglet diarrhea and the need for continuous nationwide surveillance and integrated prevention strategies.

Abstract
INTRODUCTION
MATERIALS AND METHODS
    Study design
    Sample collection
    Ethical statement
    Nucleic acid extraction
    Detection of porcine bacterial gastroenteritis pathogens
    Statistical analysis
RESULTS
    Detection of porcine bacterial gastroenteritis pathogens
    Seasonal occurrence of porcine bacterial gastroenteritispathogens
DISCUSSION
ACKNOWLEDGEMENTS
DATA AVAILABILITY STATEMENT
CONFLICT OF INTEREST
REFERENCES

• Wan-Kyu Lee(Laboratory of Veterinary Bacteriology, College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, Korea)
• Chang-Won Im(Dodram Pig Farmer’s Cooperative, Pig Special Hospital, Daejeon 35377, Korea, Laboratory of Veterinary Bacteriology, College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, Korea)
• Doo-Sung Cheon(POSTBIO Inc., Namyangju 12106, Korea) Corresponding author
• Ki-Hong Park(Bukyung Pig Farmer’s Cooperative, Pig Clinic Center, Kimhae 50966, Korea)
• Young-Ho Joo(Harim Central Research Institute, Daejeon 34047, Korea)