Objectives and methods

Objectives

The epidemiological and laboratory surveillance of invasive listeriosis in humans is the aim of the OCP-ECDC for listeriosis in Italy 

The main objectives are:

• to analyze the surveillance data of invasive listeriosis in Italy with the aim of promptly identifying epidemic outbreaks
• to implement integrated monitoring of listeriosis at national level, according to EU standards
• to carry out the integration of the data collected in the different areas (horizontal integration) and territories (vertical integration between the local, regional, and central territorial levels) to achieve the interoperability of the different information flows
• to compare the results of surveillance in Italy with those of other European countries participating in the Foodborne and Waterborne Diseases network of the ECDC
• to identify any international epidemic outbreaks

Methods

The surveillance activity of invasive listeriosis in humans is based on the collaboration, on voluntary basis, between the Istituto Superiore di Sanità and the Regional Reference Laboratories for clinical surveillance (IIZZSS), the Laboratories of the National Health Service (SSN), University Institutes and Regions.

Based on the provisions of the Circolare of the Ministry of Health 008252-13 / 03/2017-DGPRE-DGPRE-P, the above-mentioned structures send the clinical isolates of L. monocytogenes to the OCP-ECDC for listeriosis for molecular characterization by Whole Genome Sequencing (WGS). In addition to sending the bacterial strains, the laboratories that carry out sequencing in house directly insert the sequences of L. monocytogenes in a specific database, using a dedicated IT platform, whose access is password protected, and where each user can consult their own inserted sequences and compare them with those already present.

On the basis of the ECDC decision to include listeriosis among the priority diseases to be subjected to "enhanced" surveillance, also through the laboratory approach (serological and molecular typing of clinical isolates of L. monocytogenes), since 2018 the molecular methods of characterization are based on Whole Genome Sequencing (WGS). These methods replaced traditional typing techniques such as Pulsed Field Gel Electrophoresis (PFGE), which until then represented the gold standard. The presence of a centralized sequencing service at the "Grandi Strumentazioni and Core Facilities Service – FAST-NGS Area" in ISS and the development, at the SANV department, of the IRIDA-ARIES platform (https://irida.iss.it), for the collection and analysis of genomic sequences allowed Italy to rapidly complete the transition from PFGE to WGS. For the collection of strains, the OCP-ECDC for listeriosis provides a strain shipping service by courier, which collects and delivers the bacterial strains to the ISS from the facilities that request them. For most strains of L. monocytogenes, the following information on the patient is reported on the epidemiological data sheet: age, sex, residence, clinical picture, risk factors, type of biological sample, hospitalization and outcome. Epidemiological metadata are entered in the IRIDA-ARIES database in anonymized form and with the aggregation of information on residence at the regional level. Sequence analysis provides the following data: Sequence Type (ST), Clonal Complex (CC), serogroup, amplicon, Lineage, and cluster.