Neisseria meningitidis, also referred to as meningococcus, is one of the leading causes of epidemic meningitis and septicaemia worldwide. Despite modern treatment, meningococcal disease remains associated with a high mortality (about 10%). Meningococcal disease is mainly restricted to specific hypervirulent lineages and specific capsular groups (serogroups), which have a changing global distribution over time. At the end of the 2000s, the previously unusual serogroup Y emerged, corresponding to half of all of the invasive meningococcal disease (IMD) cases in Sweden by the beginning of the 2010s. The aim of this thesis is to describe the emergence of serogroup Y meningococci genetically in an effort to understand some of the factors involved in the successful spread of this group throughout Sweden. In addition, genetic typing schemes were evaluated for surveillance and outbreak investigation. Our results indicate that the currently recommended typing for surveillance of meningococci could be altered to include the factor H-binding protein (fHbp). A highly variable multilocus variable number tandem repeat analysis (HV-MLVA) was able to confirm connected cases in a suspected small outbreak. In addition, a strain type sharing the same porA, fetA, porB, fHbp, penA and multilocus sequence type was found to be the principal cause of the increase in serogroup Y disease. However, a deeper resolution obtained from the core genomes revealed a subtype of this strain, which was mainly responsible for the increase. Finally, when the Swedish serogroup Y genomes were compared internationally, different strains seemed to dominate in different regions. This indicates that the increase was probably not due to one or more point introductions of a strain previously known internationally but more probably multifactorial.

Background: Neisseria meningitidis is a gram-negative bacterium with the potential to cause invasive disease. Invasive meningococcal disease (IMD) can be fatal if delay to antibiotic therapy. There are six serogroups, which are capable of causing invasive disease in humans; A, B, C, W, X and Y. Since 2015, serogroup W and serogroup Y account for the majority of IMD cases reported in Sweden. Aim: To investigate the clinical presentations of IMD caused by Neisseria meningitidis serogroup W and Y. Method: Two databases, PubMed and Cochrane, were used to find articles that described the clinical picture of IMD. Articles with description of clinical features of the studied serogroups and with eight cases or more in every study were included. In addition, only original articles were included. Results: A total of 633 articles were found and 11 fulfilled all the inclusion criteria. Five out of seven articles found meningococcemia as the predominating presentation of serogroup W IMD. Two out of the four articles that studied serogroup Y IMD found meningitis at a higher number. Conclusion: The results of this systematic review suggest meningococcemia as a relatively common presentation of serogroup W IMD while meningitis and pneumonia might occur more frequently in serogroup Y IMD. However, these results should be interpreted carefully because the included articles were mostly retrospective studies and future prospective studies are needed to better identify clinical presentations of serogroup W and Y IMD.