To Örebro University

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.