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Escherichia Coli O157:H7 / E. coli O157:H7
1995 Case Definition

Clinical Description

An infection of variable severity characterized by diarrhea (often bloody) and abdominal cramps. Illness may be complicated by hemolytic uremic syndrome (HUS) or thrombotic thrombocytopenic purpura (TTP); asymptomatic infections also may occur.

Laboratory Criteria for Diagnosis

  • Isolation of Escherichia coli O157:H7 from a specimen, OR
  • Isolation of Shiga toxin-producing E. coli O157:NM from a clinical specimen*

Case Classification


A case of post-diarrheal HUS or TTP (see HUS case definition)


  • A case with isolation of E. coli O157 from a clinical specimen, pending confirmation of H7 or shiga toxin, OR
  • A clinically compatible case that is epidemiologically linked to a confirmed or probable case


A case that is laboratory confirmed.


Laboratory-confirmed isolates are reported via the Public Health Laboratory Information System (PHLIS), which is managed by the Foodborne and Diarrheal Diseases Branch, Division of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC. Both probable and confirmed cases are reported to the National Notifiable Diseases Surveillance System (NNDSS), but only confirmed cases are reported to PHLIS. Confirmation is based on laboratory findings, and clinical illness is not required.

*Strains of E. coli O157:H7 that have lost the flagellar "H" antigen become nonmotile and are designated "NM"