National case definition: Shiga toxin-producing Escherichia coli (STEC) Infection

Date of last revision/review: December 2023.

National notification

Only confirmed cases of disease should be notified.

Type of surveillance

Routine case-by-case notification to the federal level.

Case classification

Confirmed case

Laboratory confirmation of infection with or without clinical illness:

• Isolation of Shiga toxin-producing Escherichia coli from an appropriate clinical specimen (e.g., stool, blood, urine);
  or
• Detection of Shiga toxin antigen or nucleic acid in an appropriate clinical specimen (dependent on the test used) using a culture independent diagnostic test (CIDT), such as a nucleic acid test (NAT), or polymerase chain reaction (PCR).

Probable case

Clinical illness in a person who is epidemiologically linked to a confirmed case, which would include persons with hemolytic uremic syndrome (HUS);

or

Detection of E. coli O157 nucleic acid that is Shiga toxin negative or pending, with or without clinical illness, in an appropriate clinical specimen (i.e., dependent on the test used) using a NAT, such as a PCR.

Laboratory comments

Further strain characterization, including serotyping and molecular typing (e.g., whole genome sequencing [WGS]), is required for epidemiologic, public health, and clinical management.

A small proportion of stx1 positive specimens identified through molecular methods could be Shigella. Culture should be performed to confirm the identification.

If more than one target is positive on the gastrointestinal NAT panel, it may be indicative of a cross-reaction, co-infection and/or a single organism harbouring these genes. Reflex culture should be performed to confirm all suspect bacterial NAT signals and to meet requirements for epidemiologic, public health, and clinical management of that organism.

Clinical evidence

Clinical illness may be characterized by the following symptoms: Diarrhea (often bloody), severe abdominal pain, vomiting, and less commonly fever. Illness may be complicated by hemolytic uremic syndrome (HUS). The severity of illness may vary. While not considered clinical illness, asymptomatic infections may occur.

ICD code(s)

ICD-11 code(s):

• 1A03.3 Enterohaemorrhagic Escherichia coli infection

ICD-10 code(s)

• A04.3 Enterohaemorrhagic Escherichia coli infection

Comments

STEC includes non-O157 E. coli. Note: The organism name "STEC" is synonymous with Verotoxigenic or Verocytotoxigenic Escherichia coli (VTEC).

Probable case definitions are provided as guidelines to assist with case finding and public health management, and are not for national notification purposes.

The use of CIDTs in clinical settings as stand-alone tests for the direct detection of STEC in stool is increasing. Common CIDTs used for STEC include antigen-based tests and molecular nucleic acid tests (NATs).

Specific performance characteristics such as sensitivity, specificity, positive predictive value, and negative predictive value of these assays likely depend on the method used. It is therefore useful to collect information on the type(s) of testing performed for reported cases. However, due to the variable performance characteristics of CIDT methods and the potential for clinical sample degradation during transit, discordant results may occur between testing methods and laboratories. It is best practise to culture the CIDT positive specimen as soon as possible, such as performing culture in the laboratory that generated the CIDT positive signal. When a specimen is positive using a CIDT, it is strongly advised to collect and document information on all culture results for the specimen (i.e., CIDT+/culture+ versus CIDT+/culture– versus CIDT+/culture not done); this information is helpful to inform the development and implementation of CIDT and associated case definitions at the provincial, territorial and national levels.