CCDR: Volume 43-7-8, July 6, 2017: Outbreak detection

ISSN 1481-8531
ccdr canada communicable disease report

Increase in Neisseria meningitidis serogroup W invasive disease in Canada: 2009-2016


RSW TsangFootnote 1,Footnote *, L HoangFootnote 2, GJ TyrrellFootnote 3, G HorsmanFootnote 4, P Van CaeseeleFootnote 5, F JamiesonFootnote 6,Footnote 7, B LefebvreFootnote 8, D HaldaneFootnote 9,Footnote 10, RR GadFootnote 11, GJ GermanFootnote 12, G ZahariadisFootnote 13,Footnote 14



Background: Since 2010, there has been an increase in serogroup W Neisseria meningitidis (MenW) disease in many countries due to an emerging sequence type-11 clonal complex (ST-11 CC). In 2016, a small increase in MenW disease due to the ST-11 CC was documented in Ontario, Canada.

Objective: To examine the trends in MenW disease in Canada and to assess whether there have been changes in the type of ST clonal complex causing MenW disease between 2009 to 2016.

Methods: Invasive N. meningitidis isolates routinely submitted from across the country to the National Microbiology Laboratory were analyzed. The proportional distribution of MenW compared with other serogroups was calculated. The MenW isolates were then further characterized by serotype, serosubtype and ST clonal complex. The geographic distribution of the emerging ST-11 CC was documented and the age of patients with ST-11 CC was compared with the traditional ST-22 CC.

Results: Of the 888 invasive isolates examined, 63 were MenW giving an average annual rate of 7.1%. However, the percentage of MenW varied from 2.7% in 2012 to 18.8% in 2016. From 2009 to 2013, 91% of the MenW were typed as the traditional ST-22 CC while from 2014 to 2016, 75% were typed to be the emerging ST-11 CC. ST-11 MenW CC was documented in five provinces across Canada (British Columbia, Alberta, Manitoba, Ontario and Quebec). The median age of patients infected with the emerging ST-11 MenW CC was 53.5 years, while for patients with the traditional ST-22 CC it was 23.5 years.

Conclusion: MenW meningococcal disease is growing in prevalence in Canada and is associated with an increase in the emerging ST-11 CC. This emerging clonal complex has now been identified in five provinces in Canada. It appears to be more common in older patients than the traditional ST-22 CC, which occurs more often in younger patients.

Suggested citation: Tsang RSW, Hoang L, Tyrrell GJ, Horsman G, Van Caeseele P, Jamieson F, Lefebvre B, Haldane D, Gad RR, German GJ, Zahariadis G. Increase in Neisseria meningitidis serogroup W invasive disease in Canada: 2009-2016. Can Commun Dis Rep. 2017;43(7/8):144-9.


Invasive meningococcal disease (IMD) has been a notifiable disease in Canada since 1924 Footnote 1. It is caused by Neisseria meningitidis, which normally resides in the upper respiratory tract of healthy carriers. For reasons not completely understood, N. meningitidis may invade the blood stream and cause serious systemic infection leading to meningitis, septicemia, septic arthritis, bacteremic pneumonia and pericarditis Footnote 2. Initial clinical presentation of IMD can be nonspecific but it may progress rapidly, leading to septic shock. The disease has an average case-fatality rate of 10% Footnote 3.

N. meningitidis is classified into 12 serogroups based on antigenic specificities of their polysaccharide capsules. Most invasive diseases are caused by six serogroups: A (MenA), B (MenB), C (MenC), W (MenW), X (MenX) and Y (MenY). These invasive strains belong to a handful of genetic lineages known as hypervirulent clones, such as sequence type (ST)-32[electrophoretic type (ET)-5], ST-41/44 (lineage 3), ST-11 (ET-37), ST-8 (cluster A4), ST-5 (subgroup III) and ST-269 clonal complexes (CCs) Footnote 4,Footnote 5.

The strains causing IMD have been described as "shifting sands", with unique strains emerging with the potential to spread regionally and internationally. For example, MenA of subgroup III caused epidemics in China in the 1960s and subsequently spread to Russia and then globally Footnote 6. ET-5 MenB caused an intercontinental outbreak with a wide geographic spread that lasted for over a decade Footnote 7. The ET-15 MenC clone first emerged in Canada in the mid-1980s and led to worldwide dissemination, which ultimately led to the introduction of MenC conjugate vaccine programs in many countries. Other notable MenB clones that have caused epidemics include cluster A4 and lineage 3 Footnote 5.

The first report of MenW causing a major outbreak or epidemic occurred in 2000; this outbreak started in Saudi Arabia during the Hajj and involved more than 400 cases. The strain was characterized as ST-11 CC Footnote 8  . With pilgrims returning to their countries in Africa, Asia, Europe, North America and South America, this strain was disseminated globally. The gradual increase in MenW disease in recent years was first reported in sub-Saharan AfricaFootnote 9  and South AmericaFootnote 10Footnote 11  . Since 2010, other countries have reported an increase in IMD caused by ST-11 MenWFootnote 12 Footnote 13 Footnote 14Footnote 15.

In December 2016, Tsang et al. Footnote 16 reported an increase in invasive MenW strains in Ontario, Canada. This increase started in 2014 and was associated with a replacement of the traditional ST-22 CC with the ST-11 CC Footnote 16. There was also a small increase in the number of MenW IMD cases in that province. To determine if clonal replacement had occurred in MenW disease nationally, this study examines the trends in MenW disease and changes in clonal complex in Canada between 2009 and 2016.


Provincial public health laboratories receive case isolates from hospitals and clinical diagnostic laboratories for identification and serogroup typing. As part of the enhanced surveillance program on IMD, all provinces and territories in Canada routinely submit all their invasive N. meningitidis isolates from culture-confirmed cases to the National Microbiology Laboratory (NML) for serogroup confirmation and additional strain characterization Footnote 17. This study included all N. meningitidis isolates obtained from culture-confirmed IMD cases submitted to the NML between 2009 and 2016.

Typing of meningococci

At the NML, serogrouping is done by slide agglutination using rabbit anti-grouping antisera produced in-house and/or polymerase chain reaction (PCR) Footnote 18. Serotyping and serosubtyping is done by whole-cell enzyme-linked immunosorbent assay (ELISA) using monoclonal antibodies Footnote 19. PorA genotyping and multilocus sequence typing were conducted according to previously described standard methods Footnote 20,Footnote 21.

Geographic distribution, source and patient characteristics

Based on the requisition information provided by the provincial public health laboratories, the NML collects and analyzes information on the geographic origin of the specimens, the source (e.g. blood, cerebral spinal, pericardial or intra-articular fluid) and the age and sex of patients from whom the specimens were drawn.


Trends in MenW meningococcal disease

In Canada, between 2009 and 2016, a total of 888 N. meningitidis isolates were recovered from individual IMD cases and sent to the NML. Of these, 63 were grouped as MenW. The percentage of MenW isolates varied by year from a low of 2.7% in 2012 to a high of 18.8% in 2016 (Table 1), for an average percentage of 7.1%.

Table 1: Contribution of Neisseria meningitidis serogroup W (MenW) in culture-positive invasive meningococcal disease cases, Canada 2009-2016
Year Number of MenW case isolates Total number of IMD case isolates MenW case isolates as a percentage of IMD case isolates
Abbreviations: IMD, invasive meningococcal disease; MenW, Neisseria meningitidis serogroup W
2009 12 168 7.1%
2010 6 118 5.1%
2011 10 133 7.5%
2012 3 112 2.7%
2013 5 103 4.9%
2014 6 86 7.0%
2015 6 88 6.8%
2016 15 80 18.8%
All years 63 888 7.1%

Changes in clonal complex

The increase in the number of MenW isolates from IMD cases coincided with the identification of the ST-11 (ET-37) CC (Figure 1). From 2009 to 2013, 91% (32 out of 35) MenW isolates were typed as the traditional ST-22 CCs whereas from 2014 to 2016, only 25% (7 out of 28) MenW isolates belonged to this clonal complex. Over this same period, the emerging ST-11 CC increased from 3% (1 out of 35 isolates) to 75% (21 out of 28 isolates).

Figure 1: Clonal analysis of invasive Neisseria meningitidis serogroup W (MenW) in Canada, 2009-2016

Figure 1

Abbreviations: CC, Clonal complex; ST, sequence type

Text Equivalent - Figure 1

Figure 1: Clonal analysis of invasive Neisseria meningitidis serogroup W (MenW) in Canada, 2009-2016

Sequence Type Number of isolates received at the NML by clonal complex
2009 2010 2011 2012 2013 2014 2015 2016
Abbreviations: NML, National Microbiology Laboratory
ST-22 12 6 8 2 4 1 4 2
ST-11 0 0 1 0 0 3 5 13
ST-23 0 0 0 1 0 0 0 0
ST-167 0 0 1 0 0 0 0 0

Antigenic and genetic characterization

Almost 70% (27 out of 39) of the traditional ST-22 CC MenW isolates were typed as either W:NT (non-serotypeable):P1.6 (n=19) or W:NT:P1.- (non-serosubtypeable; n=8) with the PorA genotype of P1.18-1,3,38. Five other ST-22 MenW were typed as W:NT:P1.- with a deletion in their PorA genes. The other seven ST-22 CC MenW were non-serotypeable with serosubtype antigens of either P1.5 (n=1), P1.5,2 (n=1), P1.14 (n=2), P1.16 (n=2) or P1.- (n=1). Twelve different sequence types were identified among these 39 ST-22 CC MenW, with 15 isolates belonging to ST-184, 11 to ST-22, three to ST-8974 and two to ST-1617. The remaining eight isolates each belonged to a different sequence type (ST-1221, ST-1224, ST-1476, ST-2625, ST-3137, ST-3849, ST-8230 and ST-10188).

In contrast, 100% (all 22) of the ST-11 CC MenW isolates were typed as C:2a:P1.5,2 (n=21) or C:2a:P1.2 (n=1), with the PorA genotype of P1.5,2,36-2. Twenty-one belonged to ST-11 and one to ST-10826. There was also one MenW isolate that typed as ST-23 (ST-23 CC) and one isolate typed as ST-3705 (ST-167 CC). The former had the antigenic formula of W:19:P1.- with PorA genotype of P1.5-2,10-1,36-2 while the later was W:19:P1.5 with PorA genotype of P1.5-1,10-4,36-2.

Geographic, demographic and source data

MenW isolates of the ST-11 CC were found in British Columbia (n=5), Alberta (n=3), Manitoba (n=2), Ontario (n=8) and Quebec (n=4). The sex and age distribution of cases due to ST-22 and ST-11 CCs are shown in Table 2. For the traditional ST-22 CC MenW cases, the mean and median ages were 31.7 years and 23.5 years, respectively. The mean and median ages of patients with emerging ST-11 CC MenW were 47.9 years and 53.5 years, respectively. Eight patients under 2 years old were identified with ST-22 CC MenW; no one in this age group was diagnosed with ST-11 CC MenW. Of the ST-22 CC MenW isolates, 33 were from blood cultures, three from cerebral spinal fluid cultures, two from articular fluids and one from the pericardial fluid. Of the 22 isolates of ST-11 CC MenW from across Canada, 21 were from blood cultures and only one from cerebral spinal fluid culture.

Table 2: Demographic characteristics and specimen source for invasive Neisseria meningitidis serogroup W (MenW) cases according to clonal complex in Canada, 2009-2016
Demographics and specimen source ST-22 CC isolates
n (%)
ST-11 CC isolates
n (%)
Table 2 - Footnote 1

Shoulder, pericardial or articular fluid

Return to Table 2 - Footnote 1

Abbreviations: CC, clonal complex; n, number; ST, sequence type

Male 20 (51%) 13 (59%)
Female 19 (49%) 9 (41%)
< 12 months 4 (10%) 0
12-23 months 4 (10%) 0
2-5 years 6 (15%) 2 (10%)
6-10 years 1 (3%) 0
11-20 years 5 (13%) 4 (18%)
21-40 years 5 (13%) 2 (10%)
41-60 years 5 (13%) 7 (31%)
> 60 years 8 (21%) 7 (31%)
Unknown 1 (3%) 0
Specimen source
Blood 33 (84.6%) 21(95%)
Cerebral spinal fluid 3 (7.7%) 1 (5%)
OthersTable 2 - Footnote 1 3 (7.7%) 0
Total number of samples 39 (100%) 22 (100%)


From 2009 to 2016, while the overall number of IMD cases in Canada decreased, the percentage of cases due to MenW increased from 2.7% in 2012 to 18.8% in 2016. This increase in MenW disease was associated with a clonal shift in the MenW strain from ST-22 CC to ST-11 CC. This emerging ST-11 CC MenW clone has now been documented in five provinces. It tends to occur in middle-aged and older adults.

ST-11 CC is a long-established hypervirulent clonal complex that was first identified in 1917 in a serogroup B strain Footnote 5. In the 1960s and 1970s, ST-11 CC was associated with MenB in North America and Europe Footnote 5. In the mid-1980s, a genetic variant of ST-11 CC that caused IMD in teenagers in Ontario appeared in a MenC clone designated as ET-15 Footnote 22. Like others in the ST-11 CC, this ET-15 clone spread rapidly in North America and eventually globally Footnote 23. The MenC conjugate vaccine was first included in the publically funded childhood immunization program in the United Kingdom, in 1999 Footnote 24. In Canada, the MenC conjugate vaccine was licensed in April 2001. Beginning in 2002, some provinces started routine MenC conjugate vaccine immunisation programs and by 2007 all provinces and territories have implemented such programs Footnote 25.

The first major ST-11 CC MenW outbreak occurred during the Hajj pilgrimage in 2000. The pilgrims returning to their countries initiated the global dissemination of this clone Footnote 26. In England and Wales, the increase in the ST-11 MenW clone first became apparent in 2009/2010 Footnote 27 and its prevalence increased yearly until 2015 when a targeted vaccination program was introduced Footnote 28. A similar increase in MenW disease as a result of the same clone has been seen in Australia since 2013 Footnote 29, also leading to the introduction of a targeted vaccination program Footnote 30. The ST-11 CC MenW has now been documented in a number of other countries around the world Footnote 9,Footnote 10,Footnote 11,Footnote 12,Footnote 13,Footnote 14,Footnote 15.

The Canadian ST-11 CC MenW isolates have serotype antigen 2a and serosubtype antigen P1.5,2, typical of isolates of this clonal complex Footnote 31. They also differ antigenically from meningococci of the ST-22 CC. Currently there is no evidence to suggest that these ST-11 MenW arose by capsule switching from MenC ST-11 strain. Investigations into the MenB ST-11 that arose from MenC ST-11 by capsule switching suggest that these capsule-switched strains may not be stable for endemic spread Footnote 32. Rather, the increase in MenW ST-11 isolates in Canada and elsewhere is likely due to clonal expansion of an endemic strain Footnote 25,Footnote 26.

This study has two limitations. First, it included only bacteriologic culture-confirmed cases and not those confirmed using PCR. However, only about 10% of the IMD cases confirmed in Canada between 2006 and 2011 were diagnosed by PCR Footnote 17 and there is no evidence to suggest that PCR-diagnosed cases differ from culture-confirmed cases. Second, this study does not include data on the meningococcal vaccination history of patients with MenW. The quadrivalent meningococcal A, C, W and Y conjugate vaccine has protective immunity against MenW, but determining if any of the patients had been vaccinated prior to their illness was not possible.

Some provinces in Canada have quadrivalent meningococcal A, C, W and Y conjugate vaccine programs targeting primary or high school students Footnote 33. The protective immunity offered by this quadrivalent vaccine in the student population may have moderated the effect of the expansion of the ST-11 MenW clone in Canada. Of note, fewer MenW cases have been identified in Canada than in the United Kingdom or Australia, where a vaccine program was more recently introduced Footnote 28,Footnote 30.

It is important to note that IMD due to MenW ST-11 CC may have an atypical clinical presentation. In England, for example, a review of MenW cases in teenagers (aged 15 to 19 years) found that 7 out of 15 patients initially presented with acute gastrointestinal symptoms of nausea, vomiting and diarrhea; four were sent home from hospital, delaying the diagnosisFootnote 34. In another study of 129 MenW cases in England and Wales from 2010 to 2013, half of which were diagnosed in patients aged 45 years or above, 23% were with atypical clinical presentations of pneumonia (12%), septic arthritis (7%) and epiglottitis or supraglottitis (4%) Footnote 26. The unusual initial clinical symptoms may have implications in the early diagnosis of the disease. Timely diagnosis of IMD is important for patient treatment, contact tracing and public health control of the disease. Ongoing surveillance of these trends is indicated.


In summary, the traditional endemic MenW ST-22 CC has been replaced by an abrupt emergence of MenW ST-11 CC in five provinces in Canada. Although the overall number of MenW cases in Canada remains small, MenW is responsible for 19% of all IMD cases. Of note for clinicians and public health professionals, this ST-11 MenW clone has the potential to cause outbreaks, has occurred in an older age group in Canada and may have an atypical clinical presentation. The NML will continue its surveillance program on this disease including laboratory characterization of strains.

Authors' statement

All authors (RSWT, LH, GJT, GH, PVC, FJ, BL, DH, RRG, GJG, and GZ) are involved in the surveillance of invasive meningococcal disease in Canada. RSWT prepared the first draft and all authors contributed to the final version with comments and suggestions.

Conflict of interest



We thank the staff at the provincial public health laboratories for identifying and sending N. meningitidis isolates to the NML. We also thank Dennis Law, Jianwei Zhou, and Saul Deng for providing laboratory assistance in the analysis of strains, and the NML's DNA Core Service for providing assistance in nucleotide sequencing. The authors made use of the Neisseria Multi Locus Sequence Typing website developed by Keith Jolley and sited at the University of Oxford (BMC Bioinformatics). The development of this site was funded by the Wellcome Trust and the European Union.


Laboratory surveillance of invasive meningococcal disease is funded by the Public Health Agency of Canada.


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