L. monocytogenes causes listeriosis, a severe disease that showed the highest hospitalization rate and the highest case fatality in Europe in 2022 as well as its highest number of food-poisoning ever reported (EFSA One Health report 2022). Commission Regulation (EC) No. 2073/2005 sets down food safety criteria for enumeration of L. monocytogenes in ready-to-eat foods.
In 2009, the Belgian food competent authority – the Federal Agency for the Safety of the Food Chain (FASFC) – has designated Sciensano as national reference laboratory (NRL) for L. monocytogenes.
One of the NRL’s task is to organize proficiency tests (PT) for official laboratories and inform the competent authority about the reliability of the participant’s results.
The NRL organizes L. monocytogenes enumeration PT once a year, using one food matrix. The methods used by the participants must belong to a list of methods approved by the FASFC. They have to start the PT at a fixed date. In order to challenge the participants L. ivanovii is spiked in some blank samples. Depending on the method, confirmation tests can be essential to distinguish both species. Performance of the participants is expressed using z-score calculated based on the consensus value from participant results.
Sensitivity, specificity and the overall performance of the network were assessed on a 10 years period (2014 – 2023). The sensitivity based on 581 contaminated samples is estimated at 100 %. The specificity based on 182 blank samples not spiked with L. ivanovii is estimated at 99,4 % and the specificity based on 268 blank samples spiked with L. ivanovii is estimated at 86,9 %.
Based on all results combined the overall performance of the network is estimated at 96,5 % which is considered good even if for samples contaminated with L. ivanovii the successive rounds don’t show stable positive progress of the network.