Description of the test
Systematic typing of STEC strains
Both strains cultured at the CNR and those from external laboratories will be immediately characterised for the following parameters:
O-serogrouping, for the most frequent or important types: O157, O26, O104 (if the aaiC and/or aggR gene(s) are positive), O103, O111, and O145.
Virulence genes that are correlated with an increased risk of developing HUS:
- eaeA: intimin
- stx2a and stx2d subtypes
- enteroaggregative genes aaiC and aggR, which are only tested in the first line for stx2-positive and eaeA-negative strains
IS629 typing of STEC O157: a molecular technique for rapidly detecting epidemics caused by this serotype.
IS621 typing of STEC O26 isolates: only on special request when epidemics are suspected (not routinely reported).
Classification of STEC strains according to risk of developing HUS
Irrespective of the risks associated with the patient (mainly age < 12 years or > 75 years), the risk of developing HUS with the typed strain is assessed as follows:
Risk of developing HUS |
(Sub)type of Shiga toxin (stx)* |
|
High |
Strain positive for stx2a or stx2d |
|
Intermediate |
Strain positive for other stx2 subtypes except stx2f (with or without stx1) |
|
Low |
Positive for stx1 (without stx2) |
*The presence of the eaeA and aaiC/aggR genes has also been associated with an increased risk of developing HUS.
**In Europe, and therefore also in Belgium, a significant proportion of STEC strains are stx2f positive (ECDC, Annual Epidemiological Report for 2021). However, stx2f-positive strains have rarely been isolated from patients with HUS (De Rauw et al., 2019; Cointe et al., 2020) and are mainly associated with mild gastrointestinal symptoms (Van Hoek et al., 2023). Therefore, stx2f positive strains are reported in the low risk category for developing HUS.
Purpose of the test
On the basis of these tests, we can classify the risk of developing HUS and rapidly detect epidemics.
Criteria for carrying out this test as part of reference activities
All strains positive for a Shiga toxin gene will be analysed.
Sample instructions
See detection and confirmation of STEC in faeces
Transport instructions
See detection and confirmation of STEC in faeces
Unacceptable requests
Not applicable
Frequency of testing and turn-around time
Depending on the results, the analysis may take between 3 and 10 days.
Communication of test results
- By post for additional results from positive samples
- By Medibridge for requesting laboratories and clinicians with a link to UZ Brussel