This report presents the results of the third round of the Listeria External Quality Assessment (EQA) scheme for the typing of Listeria monocytogenes (further EQA-3). The EQA covers the Pulsed Field Gel Electrophoresis (PFGE) method, conventional serological typing and PCR-based molecular typing. A total of 22 laboratories registered forparticipation in the EQA-3 with 20 laboratories completing it and two laboratories opting out without submittingresults. The EQA-3 took place between October and December 2014.
Listeriosis is a relatively rare but serious foodborne disease, with 1 763 confirmed human cases reported in the EUin 2013 (0.44 cases per 100 000). Compared to other foodborne infections under EU surveillance, listeriosis caused the most severe human disease, with 99% of the cases hospitalised.
Since 2007, ECDC’s programme on Food- and Waterborne Diseases and Zoonoses (FWD) has been responsible for the EU-wide surveillance of listeriosis and the facilitation of the detection and investigation of foodborne outbreaks. Surveillance data, including some basic typing parameters for the isolated pathogen, are reported by Member States to the European Surveillance System (TESSy). In addition to the basic characterisation of the pathogens, more advanced and discriminatory molecular typing techniques for the surveillance of foodborne infections have been incorporated into TESSy (TESSy-MSS – ‘molecular surveillance system’) since 2012.
The objectives of this EQA are to assess the quality of PFGE and serotyping, and the comparability of the collected results produced by participating national public health reference laboratories in the European Union (EU), European Economic Area (EEA) and EU candidate countries. Strains for the EQA were selected from strains currently relevant for public health in Europe. A set of eleven strains was selected. Ten of the strains were different from one another and one was a doublet of one of the other ten strains. The set included a broad range of the clinically relevant types for invasive listeriosis.
A total of 22 laboratories participated in at least one part of the EQA-3, however two laboratories opted out of submitting any results: 18 laboratories (90%) produced PFGE results and 16 laboratories (80%) participated in the serotyping exercise. Eight of these 16 laboratories performed conventional phenotypic serotyping, while 13 performed molecular PCR-based serotyping.
The majority (67%) of the laboratories were able to produce a PFGE gel of sufficiently high quality to allow for comparison with profiles obtained by other laboratories. The gels were normalised and interpreted using the specialised software BioNumerics (BN) software. Fourteen laboratories completed the gel analysis and generally did so with high quality (93%) and in accordance with the guidelines.
The average percentage of correctly typed strains obtained for conventional serotyping was 91%, an increase from EQA-2 mainly attributed to one difficult strain included in the previous EQA. In the molecular (PCR-based) serotyping, participants obtained an average of 94% correctly typed strains which corresponds to the score obtained in EQA-2.
This EQA-3 scheme for typing of Listeria was the third EQA for laboratories participating in the FWD-Net. The number of participants were higher than in EQA-2 and EQA-1. The molecular surveillance system being implemented as part of TESSy, relies on the capacity of the European Food- and Waterborne Diseases and Zoonoses network (FWD-Net) laboratories to produce comparable typing results. Currently, the molecular typing method used for EU-wide surveillance is PFGE. Phenotypic serotyping is currently included in TESSy and PCR-based serotyping has also been included since 2012. The data submitted to TESSy are being used for surveillance purposes by several EU countries. In general, the participating countries demonstrated a high quality of serotyping.
The results of the EQA-3 for PFGE typing of Listeria demonstrate that the majority of participating laboratories were able to produce good results scoring ‘Fair’ and above in all parameters, which enables inter-laboratory comparisons. However, one third of the laboratories produced results that need to be improved in order to enable inter-laboratory exchange of data. Consequently, to achieve an acceptable quality, the technical issues identified should be overcome by optimising laboratory procedures, and providing trouble-shooting assistance and training.
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