Salmonella typing results ‘encouraging’ says ECDC
The molecular surveillance system that will be started as part of the European Surveillance System (TESSy) relies on the capacity of the Food and Waterborne Diseases (FWD)-Net laboratories to produce comparable typing results.
Results of the External Quality Assessment (EQA) cover Pulsed Field Gel Electrophoresis (PFGE), Multiple Locus Variable number of tandem repeat Analysis (MLVA) and phage typing.
The molecular typing methods used for EU-wide surveillance are PFGE for all serovars and MLVA for Typhimurium.
The objective is to assess the quality of PFGE, MLVA and phage typing and the comparability of test results between public health national reference laboratories in EU/EEA and EU candidate countries.
25 laboratories were in the PFGE part of the scheme, 56% performed MLVA typing, 44% phage typing of S. Enteritidis, and 41% phage typing of S. Typhimurium. Eight laboratories completed all three parts of the EQA.
PFGE ‘gold standard’
PFGE is still the gold standard for high discriminatory typing of Salmonella and the only generic method for typing of all Salmonella serovars, according to the report.
The majority (64%) of the laboratories 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.
Fifteen laboratories completed the gel analysis and this was generally performed in good accordance with the guidelines.
MVLA method
Although MLVA is a relatively new method, 60% of the laboratories reported correct MLVA profiles for all strains and 87% found the correct profile for at least nine of the ten strains.
Results indicate that the majority of the participating laboratories (93%) were able to perform the critical calibration of raw data and use the agreed nomenclature.
ECDC said that some of laboratories are not performing the MLVA method on a routine basis, so performance could be higher with more experience and better optimisation in each laboratory.
Phage typing
Only 41–44% of the laboratories performed phage typing of the two major Salmonella serotypes, Typhimurium and Enteritidis.
Results showed a fairly good quality of Typhimurium phage typing as 64% of laboratories reported correct results for all strains, and all laboratories found the correct phage type for at least eight of the ten strains.
More incorrect phage types were reported for the Enteritidis scheme as 42% of laboratories only reported 50–80% correct types (58% reported correct results for all strains).
Salmonellosis is the second most commonly reported zoonotic disease in EU with 97,897 cases reported by 27 EU Member States in 2011.
Salmonella is a common cause of foodborne outbreaks and is the most frequently detected causative agent in foodborne outbreaks reported to ECDC/EFSA (26.6 % of outbreaks in 2011).
“Less than half of the laboratories produced results that need to be improved for inter-laboratory exchange of data; however, for the majority of the identified technical issues, an acceptable quality is within reach by optimisation of procedures in laboratories, troubleshooting assistance, and training.”
Source: European Centre for Disease Prevention and Control
Online DOI: 10.2900/93836
“Fourth external quality assessment scheme for Salmonella typing”
