Abstract
BACKGROUND: In Ontario, serogroup W Neisseria meningitidis (MenW) accounts for a small percentage of all invasive meningococcal disease (IMD) and between 2010 and 2014, only zero to three confirmed cases occurred per year. However, between August 2015 and June 2016, six culture confirmed MenW IMD cases were reported in Ontario. OBJECTIVE: All MenW IMD cases in Ontario between January 1, 2009 and June 30, 2016 were reviewed and the N. meningitidis strains involved were characterized. METHODS: MenW cases were identified in the Integrated Public Health Information System byf Public Health Ontario. MenW isolates were characterized at the National Microbiology Laboratory. RESULTS: Of the thirteen MenW IMD cases, six were due to isolates typed as sequence type (ST)-22 clonal complex (cc), six were of ST-11 cc, and one ST-167 cc. Most (83%) MenW cases due to the ST-22 cc occurred prior to 2012 while all six MenW cases due to ST-11 cc happened since May 2014. The six MenW ST-11 isolates appeared to be clonal. CONCLUSION: It appears that a genetic shift in the invasive MenW isolates has occurred in Ontario in 2014 with the ST-11 clone replacing the traditional ST-22 clone.