Antigenic and genetic characterization of serogroup C meningococci isolated from invasive meningococcal disease cases in Canada from 1999 to 2003

The everchanging epidemiology of meningococcal disease worldwide and the potential for prevention through vaccination

Neisseria meningitidis is a major cause of bacterial meningitis and septicaemia worldwide and is associated with high case fatality rates and serious life-long complications among survivors. Twelve serogroups are recognised, of which six (A, B, C, W, X and Y) are responsible for nearly all cases of invasive meningococcal disease (IMD). The incidence of IMD and responsible serogroups vary widely both geographically and over time. For the first time, effective vaccines against all these serogroups are available or nearing licensure. Over the past two decades, IMD incidence has been declining across most parts of the world through a combination of successful meningococcal immunisation programmes and secular trends. The introduction of meningococcal C conjugate vaccines in the early 2000s was associated with rapid declines in meningococcal C disease, whilst implementation of a meningococcal A conjugate vaccine across the African meningitis belt led to near-elimination of meningococcal A disease. Consequently, other serogroups have become more important causes of IMD. In particular, the emergence of a hypervirulent meningococcal group W clone has led many countries to shift from monovalent meningococcal C to quadrivalent ACWY conjugate vaccines in their national immunisation programmes. Additionally, the recent licensure of two protein-based, broad-spectrum meningococcal B vaccines finally provides protection against the most common group responsible for childhood IMD across Europe and Australia. This review describes global IMD epidemiology across each continent and trends over time, the serogroups responsible for IMD, the impact of meningococcal immunisation programmes and future needs to eliminate this devastating disease.

Enhanced surveillance of invasive meningococcal disease in Canada, 2006-2011

Objective

The purpose of this report is to describe the epidemiology of invasive meningococcal disease (IMD) in Canada from 2006 to 2011.

Methods

Data from the Enhanced Invasive Meningococcal Disease Surveillance System and national population estimates were selected for descriptive and inferential analyses. The geographic, demographic, seasonal and subtype distributions as well as clinical characteristics of the IMD cases were examined. Incidence and mortality rates were calculated per 100,000 population per year; 95% confidence intervals (CI) were calculated for rate comparison. The direct method was used for age standardization. Proportions were compared using the chi-squared test at a p<0.05 significance level.

Results

During the study period, the mean incidence rates of IMD were 0.58 (total), 0.33 (serogroup B), 0.07 (serogroup C), 0.03 (serogroup W-135) and 0.10 (serogroup Y). The median age for serogroups B, C, W-135 and Y was 16, 43, 38 and 47 years respectively. The mean age-specific incidence rates among infants under 1 year of age (7.35, CI: 5.38-9.32) and children from 1 to 4 years of age (1.89, CI: 1.54-2.24) were significantly higher than those in any other age group. The mean case fatality ratio was 8.1% (range 4.3%-14.3%). The average number of cases that occurred per month was significantly higher (p<0.0001) in winter (18 cases) than in summer (12 cases).

Conclusion

IMD is still endemic in Canada. Although individuals at any age can be affected, infants under 1 year of age are at the greatest risk, followed by children aged 1-4 years and individuals aged 15-19 years. Following the implementation of routine childhood immunization programs with monovalent meningococcal C conjugate vaccines (MenC) in all provinces and territories (beginning in 2007), the incidence of serogroup C has decreased significantly over the study period and is now at an all-time low. Serogroup B is the leading cause of IMD, and diseases of serogroup W-135 and Y have stabilized at relatively lower incidence rates. With the addition of immunization programs using quadrivalent conjugate meningococcal vaccines (MCV4), we would expect further reductions in the incidence of meningococcal infection in Canada.

The changing epidemiology of meningococcal disease in Quebec, Canada, 1991-2011: potential implications of emergence of new strains

Background

In order to inform meningococcal disease prevention strategies, we analysed the epidemiology of invasive meningococcal disease (IMD) in the province of Quebec, Canada, 10 years before and 10 years after the introduction of serogroup C conjugate vaccination.

Methodology

IMD cases reported to the provincial notifiable disease registry in 1991–2011 and isolates submitted for laboratory surveillance in 1997–2011 were analysed. Serogrouping, PCR testing and assignment of isolates to sequence types (ST) by using multilocus sequence typing (MLST) were performed.

Results

Yearly overall IMD incidence rates ranged from 2.2–2.3/100,000 in 1991–1992 to 0.49/100,000 in 1999–2000, increasing to 1.04/100,000 in 2011. Among the 945 IMD cases identified by laboratory surveillance in 1997–2011, 68%, 20%, 8%, and 3% were due to serogroups B, C, Y, and W135, respectively. Serogroup C IMD almost disappeared following the implementation of universal childhood immunization with monovalent C conjugate vaccines in 2002. Serogroup B has been responsible for 88% of all IMD cases and 61% of all IMD deaths over the last 3 years. The number and proportion of ST-269 clonal complex has been steadily increasing among the identified clonal complexes of serogroup B IMD since its first identification in 2003, representing 65% of serogroup B IMD in 2011. This clonal complex was first introduced in adolescent and young adults, then spread to other age groups.

Conclusion

Important changes in the epidemiology of IMD have been observed in Quebec during the last two decades. Serogroup C has been virtually eliminated. In recent years, most cases have been caused by the serogroup B ST-269 clonal complex. Although overall burden of IMD is low, the use of a vaccine with potential broad-spectrum coverage could further reduce the burden of disease. Acceptability, feasibility and cost-effectiveness studies coupled with ongoing clinical and molecular surveillance are necessary in guiding public policy decisions.

Genetic and antigenic analysis of invasive serogroup C Neisseria meningitidis in Canada: A decrease in the electrophoretic type (ET)-15 clonal type and an increase in the proportion of isolates belonging to the ET-37 (but not ET-15) clonal type during the period from 2002 to 2009

BACKGROUND

Serogroup C meningococcal disease has been endemic in Canada since the early 1990s, with periods of hyperendemic disease documented in the past two decades. The present study characterized invasive serogroup C meningococci in Canada during the period from 2002 to 2009.

METHODS

Serogroup C meningococci were serotyped using monoclonal antibodies. Their clonal types were identified by either multilocus enzyme electrophoresis or multilocus sequence typing.

RESULTS

The number of invasive serogroup C Neisseria meningitidis isolates received at the National Microbiology Laboratory (Winnipeg, Manitoba) for characterization has dropped from a high of 173 isolates in 2001 to just 17 in 2009, possibly related to the introduction of the serogroup C meningococcal conjugate vaccine. Before 2006, 80% to 95% of all invasive serogroup C meningococci belonged to the electrophoreic type (ET)-15 clonal type, and the ET-37 (but not ET-15) type only accounted for up to 5% of all isolates. However, beginning in 2006, the percentage of the ET-15 clonal type decreased while the ET-37 (but not ET-15) type increased from 27% in 2006 to 52% in 2009. The percentage of invasive serogroup C isolates not belonging to either ET-15 or ET-37 also increased. Most ET-15 isolates expressed the antigenic formula of C:2a:P1.7,1 or C:2a:P1.5. In contrast, the ET-37 (but not ET-15) isolates mostly expressed the antigens of C:2a:P1.5,2 or C:2a:P1.2.

CONCLUSION

A shift in the antigenic and clonal type of invasive serogroup C meningococi was noted. This finding suggests vigilance in the surveillance of meningoccocal disease is warranted.

Meningococcal vaccines and herd immunity: lessons learned from serogroup C conjugate vaccination programs

Effective vaccines provide direct protection to immunized individuals, but may also provide benefits to unvaccinated individuals by reducing transmission and thereby lowering the risk of infection. Such herd immunity effects have been demonstrated following the introduction of meningococcal serogroup C conjugate (MCC) vaccines, with reductions in disease attack rates in unimmunized individuals and significantly lower serogroup C carriage attributable to the vaccine introduction. In the UK, targeting teenagers for immunization was crucial in maximizing indirect effects, as most meningococcal transmission occurs in this age group. Questions remain regarding the duration of herd protection and the most appropriate long-term immunization strategies. The magnitude of the herd effects following MCC vaccination was largely unanticipated, and has important consequences for the design and evaluation of new meningococcal vaccines.

Population-based seroprevalence of Neisseria meningitidis serogroup C capsular antibody before the introduction of conjugate vaccine, in Australia

Neisseria meningitidis serogroup C (NMC) conjugate vaccine was introduced, in Australia, in 2003. Our aims were to determine pre-immunisation IgG NMC seroprevalence and evaluate an enzyme-linked immunosorbent assay (ELISA), previously validated against the serum bactericidal assay (SBA). 2409 sera, collected in 2002, from subjects aged 2-34 years, were tested. The geometric mean concentration (GMC) of NMC anticapsular IgG was 0.38 U/mL in subjects under 19 years and it increased to 0.67 U/mL for those aged 30-34 years. Variation in GMC correlated with reported NMC disease incidence and was higher in males than females (0.52 U/mL versus 0.41 U/mL; p=0.005). The ELISA appears suitable for serosurveillance but the IgG level that correlates with protection needs further investigation. Serosurveys will be repeated to monitor the impact of vaccination.

Invasive meningococcal disease in Quebec, Canada, due to an emerging clone of ST-269 serogroup B meningococci with serotype antigen 17 and serosubtype antigen P1.19 (B:17:P1.19)

During periods of endemic meningococcal disease, serogroup B Neisseria meningitidis is responsible for a significant percentage of invasive diseases, and no particular clone or strain predominates (F. E. Ashton and D. A. Caugant, Can. J. Microbiol. 47: 293-289, 2001), However, in the winter of 2004 to 2005, a cluster of serogroup B meningococcal disease occurred in one region in the province of Québec, Canada. The N. meningitidis strain responsible for this cluster of cases was identified as sequence type ST-269 with the antigenic formula B:17:P1.19. Retrospective analysis of isolates from 2000 onwards showed that this clone first emerged in the province of Québec in 2003. The emergence of this clone of serogroup B meningococci occurred after a mass vaccination against serogroup C N. meningitidis, suggesting possible capsule replacement.