A - Faecal PCR at SERL

Faecal sample processing should be in line with the Scottish Health Protection Network guidance on laboratory diagnosis (revised 2018 www.hps.scot.nhs.uk/web-resources-container/guidance-for-the-public-health-management-of-escherichia-coli-o157-and-other-shiga-toxin-producing-stec-infections/) which advises the processing of faeces for STEC in the following situations:

  • Cases of suspected HUS or cases of bloody diarrhoea in whom conventional laboratory testing has failed to yield a pathogen;
  • All symptomatic contacts of non-sorbitol fermenting (NSF) E. coli O157, sorbitol fermenting (SF) E. coli O157 and non-O157 STEC in whom conventional laboratory testing has failed to yield a pathogen;
  • Any outbreak-associated case in whom conventional laboratory testing has failed to yield a pathogen.

Faecal PCR is no longer considered a Reference Laboratory test, however SERL continues to offer this on a pay per test basis (whereby NHS Boards are retrospectively charged for this service). There is currently no additional cost for subsequent isolation of the organisms and additional typing.

B - Isolation from PCR positive faeces and typing

Real-time PCR is carried out on submitted faeces to detect the presence of E. coli O157 (stx positive and negative strains) and non-O157 STEC. If PCR positive, the organisms are cultured, where possible, and then typed, including whole genome sequencing (WGS).

Please Note: it can take a considerable period of time to isolate an organism from a PCR positive faecal sample, particularly if we are trying to culture a non-O157 STEC.

C - Processing of Submitted Isolates

The SERL receives isolates of E. coli O157 for confirmation of identity and typing by WGS.

D - Clearance Samples

i - Non-Sorbitol Fermenting E. coli  O157

Microbiological clearance for NSF E. coli O157 (with or without stx genes) is confirmed by conventional culture at the local diagnostic laboratory, irrespective of whether or not the local lab initially cultured the STEC.

ii - Sorbitol Fermenting E. coli  O157 and Non-O157 STEC

Microbiological clearance for SF E. coli O157 and non-O157 STEC is confirmed at SERL by PCR for the detection of rfbO157, stx1 and stx2. Samples will be reported by SERL as positive or negative based on interpretation of the PCR result.

Diagnostic labs employing PCR methodology for STEC detection may be able to locally confirm microbiological clearance of SF and non-O157 STEC.

E - Atypical HUS

Certain Scottish patients may be referred to the aHUS National Specialist Centre in Newcastle, who coordinate the use of Eculizumab. Faecal PCR testing to exclude STEC should still be carried out at SERL. SERL will communicate results to the submitting laboratory and the Specialist Centre in Newcastle.

F - E. coli  Serodiagnosis

From March 2020, UKHSA discontinued the E. coli serodiagnostic service, so please DO NOT send sera to the SERL for E. coli serology. This is no longer part of our scope of service and this test is no longer performed in the UK. If patients have symptoms consistent with STEC infection, please submit faecal samples.