As is the case in the rest of Europe, the annual incidence of Listeria monocytogenes infections in humans significantly increased over the years. Over the last 18 years, the incidence rates varied between 0.4 and 0.9 cases/100 000 inhabitants, which is relatively high compares to other European countries (average of 0.43/100 000 inhabitants, ECDC report 2016). This increasing trend is mainly due to an increase of non-maternal-neonatal (n-MN) cases, since maternal-neonatal (MN) cases have been decreasing over the years. This latter is a consequence of active prevention campaigns targeting pregnant women. However, in 2018 a relatively high number of 11 MN cases were reported.
In Belgium, listeriosis is a notifiable infectious disease, and strains are voluntarily sent to the National Reference Center (NRC). Identity confirmation is performed using biochemical assays and serotyping by slide agglutination. Since 2018, according to recent evolution in molecular typing, the NRC completely switched to Whole-Genome-Sequencing (WGS) for cluster detection. Therefore, an in-house Galaxy-based bio-informatic pipeline was developed. For the strain collection from 2010 until 2017 both classical data (MLST and PFGE) as cgMLST data are available.
Of all confirmed L. monocytogenes cases in humans, serotypes 1/2a and 4b are most frequently observed. During the period 2000-2018, they comprise 47.1% and 36.2% of the cases, respectively. Notably, the incidence of serotype 4b remains rather stable, while the increase of serotype 1/2a is in relation with the increase of the overall incidence of Listeria cases. The number of sporadic 1/2a cases (unique pulsovars or cgMLST profiles) remained stable, whereas the proportion of cases related to clusters corresponded with the fluctuating annual incidence. Antibiotic resistance to antimicrobials remains a rare event among L. monocytogenes isolates, although a significant increase of MIC50 and MIC90 values for ciprofloxacin resistance were noted recently (Bertrand et al, 2016).