Fourth external quality assessment scheme for typing of verocytotoxin-producing E. coli (VTEC)

Twenty-eight public health national reference laboratories from 28 EU/EEA countries signed up for the fourth international external quality assessment (EQA) scheme on typing of VTEC organised by ECDC. Seventy-one per cent (20 out of 28) of the laboratories participated in the pulsed-field gel electrophoresis (PFGE) part of the EQA, and 50% of the participants were able to produce a PFGE gel of sufficiently high quality to allow for the profiles to be comparable to profiles obtained by other laboratories. The subsequent normalisation and interpretation of the profiles were performed using the specialised software suite BioNumerics (BN). Twelve laboratories (60%, 12 out of 20) completed the gel analysis and 50% performed in a fair to good accordance with the guidelines. Thirteen (46%) laboratories participated in full O:H serotyping, and 50% of the participating laboratories were able to correctly determine the full O:H serotype of the 15 test strains that were included in the fourth EQA. Correct typing of virulence genes was 96% for eae, 98% for vtx1 and 99% for vtx2 and ehxA. Subtyping of vtx was performed correctly by 94% of the participants for the three vtx1 subtypes, and by 93% for the four vtx2 subtypes included in this EQA. Correct phenotypic characterisation was high, from 89% for VT production to 100% for ESBL production. This report presents the results of the fourth round of the external quality assessment scheme for typing of verocytotoxin-producing E. coli (VTEC) funded by ECDC. The fourth EQA was carried out from November 2012 to February 2013 and included the following methods: pulsed-field gel electrophoresis (PFGE), O:H serotyping, detection of virulence genes (eae, vtx1, vtx2 and ehxA), subtyping of the vtx genes, phenotypic detection of verocytotoxin/Shiga toxin production (VT/Stx), fermentation of sorbitol, production of β-glucuronidase, enterohaemolysin, and extended β-lactamase (ESBL). Although the majority of reported human VTEC infections