Increase in Endemic Neisseria meningitidis Capsular Group W Sequence Type 11 Complex Associated With Severe Invasive Disease in England and Wales

Background. In England and Wales, the incidence of invasive meningococcal disease has been declining for more than a decade, but meningococcal group W (MenW) cases have been increasing since 2009. Methods. Public Health England conducts enhanced national surveillance of invasive meningococcal disease in England and Wales. Detailed clinical information was obtained for all laboratory-confirmed MenW cases diagnosed during 3 epidemiologic years (2010-2011 to 2012-2013), alongside whole-genome sequencing analysis of the clinical isolates. Results. The year-on-year increase in invasive MenW disease across all age groups since 2009-2010 was due to rapid endemic expansion of a single clone belonging to the sequence type 11 complex (cc11). In 2013-2014, MenW was responsible for 15% of all invasive meningococcal disease. All but 1 of the recent MenW: cc11 isolates were very closely related, consistent with recent clonal expansion. Clinical follow-up of all 129 MenW cases diagnosed during 2010-2011 to 2012-2013 revealed that most patients were previously healthy (n = 105 [81%]), had not travelled abroad prior to illness and the majority presented with septicemia (n = 63 [49%]), meningitis (n = 16 [12%]) or both (n = 21 [16%]); however, one-quarter had atypical presentations including pneumonia (n = 15 [12%]), septic arthritis (n = 9 [7%]), and epiglottitis/supraglottitis (n = 5 [4%]). Forty-eight (37%) required intensive care and 15 (12%) died. There was no association between infecting strain, clinical disease, or outcome. Conclusions. The recent increase in invasive MenW disease in England and Wales is due to rapid endemic expansion of a single clone belonging to cc11 and is associated with severe disease with unusual clinical presentations. This increase will require careful monitoring in the coming years.