Unusual meningitis cases in Canada

Increase in ST-11 serogroup W Neisseria meningitidis invasive meningococcal disease in Canada, 2016–2018. Tsang RS*, Hoang L, Tyrrell GJ, Minion J, Van Caeseele P, Kus JV, Lefebvre B, Haldane D, Garceau R, German G, Zahariadis G, Hanley B. Can Commun Dis Rep 2019 Jun 6; 45(6):164-9. doi: https://doi.org/10.14745/ccdr.v45i06a04

This science story explains the emergence of a highly infectious strain of Neisseria meningitidis in Canada. This work is an example of how laboratory-based surveillance activities help us better understand and control the spread of infectious organisms responsible for vaccine preventable bacterial diseases.

What was known about this area prior to your work, and why was the research done?

Invasive meningococcal disease (IMD) caused by Neisseria meningitidis (N. meningitidis) is a serious condition that can lead to swelling of tissues surrounding the brain, bloodstream infections and may be fatal in some cases (10-15%). IMD in some patients (approximately 20%) can result in long-term health consequences, such as hearing loss or amputation. Most IMD in the world is caused by six of the twelve known N. meningitidis serogroups. Serogrouping is a way to classify distinct variations of N. meningitidis based on the outer envelope of the bacteria which is a key virulence determinant. The serogroup classifications help researchers better understand and track different strains of the disease. The majority of Canadian cases over the last two decades were caused by serogroups B, C, Y and W of N. meningitidis. In response to these cases, vaccines protecting against the four main serogroups of A, C, W, and Y are now used in most jurisdictions for immunization programs with serogroup B vaccines offered separately. Vaccination programs have resulted in a dramatic decrease of MenC disease for infants and teenagers since they were commenced in the early 2000’s. Despite this progress, an increase in serogroup W (MenW) disease has been noted since 2014 in a number of provinces. This study provides an update on this increase of invasive MenW disease in Canada while describing strain characteristics and case demographics.

What are your most significant findings from this work?

The NML conducts routine bacterial characterization on provincial submissions of IMD specimens. This additional typing data helps to classify the specimens and is used to inform the national surveillance of IMD. Based on these submissions, it was noted that more IMD cases were caused by MenW in 2018 than serogroups B, C, or Y meningocicci. This was never seen before and is likely linked to the global emergence and spread of a virulent MenW strain (ST-11 CC¬). MenW disease caused by this strain has been associated with unusual signs and symptoms of illness, rapid disease progression and a high case fatality rate. More than half of the cases in this study were from patients 30 years and older which is unusual as the disease typically affects infants, young children, teens and youth or the elderly. Overrepresentation of this MenW disease in adults may inform vaccination strategies to control and limit the potential spread of this MenW strain.

What are the implications or impact of the research?

This study identifies and characterizes a recent increase of IMD as attributed to MenW ST-11 CC. This MenW strain is preventable by current meningococcal vaccines. A targeted vaccination program used in British Columbia controlled a localized outbreak of MenW ST-11 CC. The ease in spreading IMD causing bacteria as well as the burden of disease are important considerations in determining when and how vaccines would be used. In addition, to help further detect and control MenW infections, frontline physicians may need to be proactive if they suspect meningococcal infections by providing prompt antibiotic treatment and initiating laboratory investigations. The emergence of newer types and unusual strains of N. meningitidis highlight the importance and necessity of ongoing strain characterization in IMD surveillance and research. This type of strain characterization work may also contribute to informing vaccine policy to better protect Canadians from emerging and harmful strains.

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