The aim of the gene determination scheme is to evaluate laboratories capacity to determine  the most important virulence factors and pathogenicity potential of STEC isolates. Virulence  gene testing should include the detection and typing of the following genes; intimin (e a e),  verotoxin1 and verotoxin2, subtyping of v tx 1 (a, c, d), and v tx 2 (a, b, c, d, e, f, g),  chromosome protein gene (aai C) and enteroaggregative adhesions transcription regulator  gene (a g R).  In the cluster analyses part of the EQA the aim is to assess the participant’s ability to identify  clusters of genetically closely related isolates given the fact that a multitude of different  laboratory and analytical methods are used as the primary cluster detection approach in  Member States. It assesses the participants’ ability to reach the correct conclusion, i.e.  correctly categorise cluster test isolates, instead of the ability to follow a specific procedure  Laboratories are expected to use their standard procedure for serotyping and correctness of  the typing results shall be evaluated by the contractor independently of the method used  (either phenotypic serotyping or molecular typing methods). In addition, the contractor should  collect the information on the methods and material used for serotyping by each participant  and summarise the results in the EQA report (see DL7 and DL8).  Laboratories should use their standard procedure for virulence gene determination and  correctness of the results shall be evaluated by the contractor independently of method used  (e.g. PCR, virulence prediction using WGS data). Contractor should collect the information on  the methods used for virulence gene detection by each participant and summarise the results  in the EQA report (see DL7 and DL8).  Laboratories are expected to use their routinely used methods (PFGE, MLVA or/and derived  data from the whole genome sequencing (WGS). Laboratories performing WGS can use their  own analysis pipeline for the cluster analysis e.g. single nucleotide polymorphism analysis  (SNP-based) or whole genome multi locus sequence typing (cgMLST/wgMLST). The  contractor shall:  ST 3. Molecular typing -based cluster analyses ST 2. Virulence gene determination ST 1. Serotyping 1. Based on pre-defined categorisation evaluate participants’ ability to assess genetic  relatedness of the provided test isolates and correct identification of the cluster (see DL4  and DL8);  2. Provide a set of extra genomes and asses laboratories’ ability to determine whether these  are part of the pre-defined cluster (see DL3); 3. Collect and analyse the raw reads and the quality of sequence data and sequence types of  the test isolates uploaded by participants when WGS is performed (see DL7 and DL8); 4. Communicate with participants when identifying problems and offer expert advice and  trouble-shooting services to the laboratories not able to achieve acceptable level of  performance in the EQA exercise (see DL4);  5. Evaluate the correctness and inter-laboratory comparability of the results of the cluster  analysis among the participants (see DL8);  6. Collect information about the analytical approach, tools and methods of the WGS-based  cluster analyses in participating laboratories and summarise the results in the EQA report  (see DL7 and DL8).  14 