A DECADE OF SOURCE TRACING INVASIVE LISTERIA MONOCYTOGENES INFECTIONS IN ISRAEL

Listeria monocytogenes (Lm) infection (listeriosis) is an uncommon but potentially fatal foodborne illness that mainly inflicts individuals with risk factors such as the elderly, the immunocompromised, pregnant women and their fetuses.

Isolates are routinely referred from clinical and food laboratories to the National Listeria Reference Center of the Ministry of Health. Since 2007, all Lm isolates are characterized by pulsed-field gel electrophoresis (PFGE) according to PulseNet protocols, which is considered the gold standard for Lm epi-typing. To date, 509 clinical isolates and more than 800 food isolates were analyzed, comprising a national database for strain tracking and outbreak investigation.

PFGE analysis of clinical isolates revealed high diversity, with more than 150 different pulsotypes. While most listeriosis cases were sporadic, 27 clusters of clonal food and clinical strains (consisting of 2-50 isolates each) were identified. Of these 27 clusters, 21 were associated with ready-to-eat (RTE) foods, 5 with fresh fish and 1 restaurant point-source. Notable clusters included isolates from RTE salads (11 isolates), smoked uncooked fish (5) and fresh fish (5). The clusters comprising the most clinical isolates were associated with fresh fish (14 clinical cases), smoked fish (11), cakes (6), salads (6) and pastrami (5). During recent years, the genotyping results are regularly communicated to the National Food Services, allowing identification of implicated foods (such as contaminated fresh and smoked fish) and institution of corrective actions at fish plants in Israel and overseas.

Recently, Whole Genome Sequencing (WGS) for L. monocytogenes has been applied by PulseNet for international surveillance, thereby improving outbreak detection and investigation. We are in the process of implementing WGS at the NLRC to further augment food safety in Israel.