| Summary: | This study aimed to determine the prevalence of several pathovirotypes and evaluate the association of haemolysis with the virotypes of pathogenic <i>E. coli</i> isolated from post-weaning piglets in South Korea from 2015 to 2019. We isolated 890 <i>E. coli</i> and tested for O-serogroups, virulence genes, haemolysis, and multilocus sequence typing. The predominant virotypes were STb:EAST1:AIDA-I, F18b:Stx2e:AIDA-I, F18:STa:STb:Stx2e, and eae:Paa in enterotoxigenic <i>E. coli</i> (ETEC), Shiga toxin-producing <i>E. coli</i> (STEC), ETEC/STEC, and enteropathogenic <i>E. coli</i> (EPEC), respectively. Regarding serogroups, O139, O149, O141, and O121 were mostly detected in F18:Stx2e:AIDA-I, F4:LT:STb:EAST1, F18:STa:STb, and F18:Stx2e:EAST1, respectively. There was a significant change in the frequency of the O141:F18ac:STa:STb (an increase from 1.6% to 10.1%) and O139:F18ab:Stx2e:AIDA-I (a decrease from 13.0% to 5.3%) virotypes in ETEC and STEC, respectively, from 2015 to 2019. The O141:F18ac:STa:STb virotype was mostly detected in the central area and was spreading to the southern area. The odds ratios between haemolysis and virotypes were 11.0, 6.25, and 8.57 in F18:STa:STb, F18:Stx2e:AIDA-I, and F4:LT:STb:EAST1, respectively. Our findings provide insights regarding the recent prevalence of pathogenic <i>E. coli</i> in South Korea and could be used for the development of vaccines for <i>E. coli</i> responsible for PWD and ED in post-weaning piglets.
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