Dottorato in MALATTIE INFETTIVE, MICROBIOLOGIA E SANITA' PUBBLICA

Titolo della tesi: Twenty years of serogroup C Invasive Meningococcal Disease in Italy

Abstract Introduction. Since meningococci of serogroup C (MenC) belonging to clonal complex 11 (cc11) are considered highly virulent and able to cause outbreaks, it is important to identify and characterize this aggressive, vaccine preventable strain. In Italy, the introduction of the meningococcal C conjugated vaccine (MCC) in 2005 has led to a reduction in the cases of MenC disease, mostly among children for whom the vaccination is targeted. However, invasive meningococcal diseases (IMD) due to MenC:cc11 strains are still spreading through the country with high morbidity and mortality. The aim of this study was to describe the epidemiology of MenC in Italy in 20-years period, from 2000 to 2019. Moreover, phenotypic and molecular features, including genetic relationships among MenC strains from sporadic cases and outbreaks occurred in the country, were analysed. Material and Methods. Bacterial isolates and clinical samples (blood or cerebrospinal fluid) from IMD cases are collected and characterized by the National Reference Laboratory (NRL) at Istituto Superiore di Sanità in Rome. Antimicrobial susceptibility was determined by MIC Test Strip Method, using the EUCAST breakpoints. Genotypic characteristics, including genogroup identification, multilocus sequence typing (MLST), antigen finetype (Porin A Variable Regions 1 and 2 –VR1 and VR2- and the iron-regulator protein FetA VR), will be performed following standard procedures. The genotypic formula is identified as follows: capsular group: PorA(P1.)VR1,VR2:FetA VR:ST(cc). The complete genome sequences of meningococcal strains were obtained using Illumina MiSeq Platform and analysed on the Neisseria.org website using the core genome MLST (cgMLST) tool. Results. A total of 1002 laboratory confirmed cases due to MenC were reported within the National Surveillance System (http://old.iss.it/mabi/). The MenC IMD showed an average annual incidence of 0.08 per 100 000 population, with peaks of 0.17 in 2005 and 0.10-0.13/100 000 in 2015-2016. The median age of IMD patients was 20 years. The main clinical pictures were sepsis, meningitis and meningitis/sepsis. During the 20-yers period, six outbreaks caused by MenC:cc11 occurred in Italy. Overall, 4% of MenC strains were resistant to ciprofloxacin, rifampicin or penicillin, whereas the 69% showed a decreased susceptibility to penicillin G. Fourteen different ccs (cc11 was the predominant), and 27 genotypic formulas were identified, of them the most frequent was C:P1.5-1,10-8:F3-6:ST-11(cc11) responsible of several outbreaks occurred in Italy, with a high case fatality rate. Whole genome sequencing was performed on MenC strains collected since 2012 and compared using a “gene-by-gene” approach available through the PubMLST Genome Comparator. Genomes were clustered by ccs; in particular, MenC:non-cc11 grouped together, whereas MenC:cc11 splitted in subgroups. Discussions and Conclusions. In Italy, MenC continues to be responsible of severe IMD cases and outbreaks. From 2000 to 2019, the C:P1.5-1,10-8:F3-6:ST-11(cc11) is the main strain identified causing sporadic cases and outbreaks, in line with other European countries. In the post vaccination era, the monitoring and the genomic analysis of MenC meningococci should be maintained in order to assess the genetic diversity of meningococcal strains, identify emerging clone and track their spread during outbreaks and epidemics.