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Shiga Toxin-producing Escherichia coli (STEC)
2018 Case Definition

CSTE Position Statement(s)

  • 17-ID-10

Background

Shiga toxin-producing Escherichia coli (STEC) are estimated to cause more than 265,000 illnesses each year in the United States. STEC can cause illness that ranges from mild diarrhea to bloody diarrhea and life-threatening hemolytic uremic syndrome (HUS). STEC are categorized into serogroups by their somatic O antigen. The STEC serogroup most commonly identified and associated with severe illness and hospitalization in the United States is E. coli O157; however, there are over 50 other serogroups that can also cause illness. The majority of infections are not reported to public health, because many individuals do not seek health care or are not tested. In recent years, the number of clinical laboratories that use tests that detect Shiga toxin or Shiga toxin genes has increased, resulting in increased detection of both O157 and non-O157 STEC infections.

Ongoing surveillance of STEC infections is essential to detect and control outbreaks, to determine public health priorities, to monitor trends in illness, and to assess effectiveness of public health interventions. Methods for surveillance must keep pace with changing laboratory diagnostic methods.

Clinical Criteria

An infection of variable severity characterized by diarrhea (often bloody) and/or abdominal cramps. Illness may be complicated by HUS (note that some clinicians still use the term thrombotic thrombocytopenic purpura [TTP] for adults with post-diarrheal HUS).

Laboratory Criteria for Diagnosis

Confirmatory laboratory evidence

  • Isolation of E. coli O157:H7 from a clinical specimen OR
  • Isolation of E. coli from a clinical specimen with detection of Shiga toxin or Shiga toxin genes.

Supportive laboratory evidence

  • Isolation of E. coli O157 from a clinical specimen without confirmation of H antigen, detection of Shiga toxin, or detection of Shiga toxin genes, OR
  • Identification of an elevated antibody titer against a known Shiga toxin-producing serogroup of E. coli, OR
  • Detection of Shiga toxin or Shiga toxin genes in a clinical specimen using a culture-independent diagnostic test (CIDT) and no known isolation of Shigella from a clinical specimen. OR
  • Detection of E. coli O157 or STEC/ Enterohemorrhagic E. coli (EHEC) in a clinical specimen using a CIDT.

Epidemiologic Linkage

A clinically compatible illness in a person that is epidemiologically linked to a confirmed or probable case with laboratory evidence OR

A clinically compatible illness in a person that is a member of a risk group as defined by public health authorities during an outbreak.

Criteria to Distinguish a New Case from an Existing Case

A new case should be created when a positive laboratory result is received more than 180 days after the most recent positive laboratory result associated with a previously reported case in the same individual. (See formula referenced in Appendix B of the 2017 CSTE Position Statement [17-ID-10] for details on time period calculation, hierarchy of dates and interpretation). OR

When two or more different serogroups/serotypes are identified in one or more specimens from the same individual, each serogroup/serotype should be reported as a separate case.

Case Classification

Suspected

  • Identification of an elevated antibody titer against a known Shiga toxin-producing serogroup of E.coli in a person with no known clinical compatibility, OR
  • Detection of Shiga toxin or Shiga toxin genes in a clinical specimen using a CIDT and no known isolation of Shigella from a clinical specimen in a person with no known clinical compatibility, OR
  • Detection of E. coli O157 or STEC/EHEC in a clinical specimen using a CIDT in a person with no known clinical compatibility, OR
  • A person with a diagnosis of post-diarrheal HUS/TTP (see HUS case definition).

Probable

  • A person with isolation of E. coli O157 from a clinical specimen without confirmation of H antigen, detection of Shiga toxin or detection of Shiga toxin genes, OR
  • A clinically compatible illness in a person with identification of an elevated antibody titer against a known Shiga toxin-producing serogroup of E. coli, OR
  • A clinically compatible illness in a person with detection of Shiga toxin or Shiga toxin genes in a clinical specimen using a CIDT and no known isolation of Shigella from a clinical specimen, OR
  • A clinically compatible illness in a person with detection of E. coli O157 or STEC/EHEC from a clinical specimen using a CIDT, OR
  • A clinically compatible illness in a person that is epidemiologically linked to a confirmed or probable case with laboratory evidence, OR
  • A clinically compatible illness in a person that is a member of a risk group as defined by public health authorities during an outbreak.

Confirmed

  • A person that meets the confirmatory laboratory criteria for diagnosis.

Comments

Asymptomatic infections and infections at sites other than the gastrointestinal tract in people (1) meeting the confirmatory laboratory criteria for diagnosis or (2) with isolation of E. coli O157 from a clinical specimen without confirmation of H antigen, detection of Shiga toxin, or detection of Shiga toxin genes, are considered STEC cases and should be reported.

Although infections with Shiga toxin-producing organisms in the United States are primarily caused by STEC, in recent years an increasing number are due to infections by Shiga toxin-producing Shigella. Persons with (1) detection of Shiga toxin or Shiga toxin genes using a CIDT and (2) isolation of Shigella spp. from a clinical specimen should not be reported as an STEC case.

Due to the variable sensitivities and specificities of CIDT methods and the potential for degradation of Shiga toxin in a specimen during transit, discordant results may occur between clinical and public health laboratories. Persons with (1) detection of Shiga toxin or Shiga toxin genes using a CIDT and (2) the absence of isolation of Shigella from a clinical specimen, should be classified as a suspect or probable case, regardless of whether detection of Shiga toxin or Shiga toxin genes is confirmed by a public health laboratory.

Reference(s)

  1. Council of State and Territorial Epidemiologists. Public Health Reporting and National Notification for Shiga Toxin-Producing Escherichia coli (STEC). Atlanta, GA: Council of State and Territorial Epidemiologists; 2017. http://c.ymcdn.com/sites/www.cste.org/resource/resmgr/2017PS/2017PSFinal/17-ID-10.pdf


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