Emergence of Escherichia coli Hybrid Pathotype ETEC/STEC: A Macroepidemiological Approach of Molecular Characterization in the United States Swine Population.

Escherichia coli-associated diseases continue to be a significant concern in swine health. Disease may occur when E. coli strains harbor specific virulence factors. The combination of virulence factors detected in a single isolate forms a virotype, which can be grouped into pathotypes based on mechanisms of pathogenicity. This study compiled E. coli polymerase chain reaction (PCR) sample-level data from six major U.S. veterinary diagnostic laboratories (VDLs) to evaluate trends in E. coli virulence factors, virotypes, and pathotypes from porcine cases. The dataset contained diagnostic results for E. coli virulence factors detected by PCR, including attachment genes (fimbriae and adhesins) and toxin genes (heat-labile, heat-stable, and Shiga-like toxins). Between 2008 and 2025, major shifts were observed in the detection of key E. coli virulence factors. Temporal trend analysis using the Mann-Kendall test showed increasing detection of the virulence factors F18, F41, STa, Stx2, and Stx2e, while F4, AIDA, Paa, and EAST1 decreased over time. Similar patterns were observed among isolates classified as potentially pathogenic, with increases in F18, F41, STa, Stx2, and Stx2e and decreases in F4, AIDA, Paa, and EAST1 detection. Among pathotypes, Hybrid enterotoxigenic E. coli (ETEC)/STEC had an increase in detection over time, whereas ETEC, STEC, and isolates classified as not potentially pathogenic decreased. This large-scale diagnostic dataset reveals a notable shift in the E. coli pathogenic profile in swine over the past decade, characterized by an increasing detection of the hybrid ETEC/STEC pathotype and evolving virotype compositions.