Enterohemorrhagic microorganisms are those that, as part of their pathogenesis, cause bloody diarrhea and colitis. While many pathogens are enterohemorrhagic, most cases observed are derived of E. coli serotype O157:H7. The E. coli O104:H4 strain identified as the cause of the 2011 outbreak in Germany is also enterohemorrhagic. These enterohemorrhagic E. coli strains, collectively also known as EHEC, release verotoxin, which further can cause hemolytic-uremic syndrome.