Abstract
The purpose of this report is to describe the epidemiology of invasive meningococcal disease (IMD) in Canada from 2006 to 2011. 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. 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). 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.
Highlights
Invasive meningococcal disease (IMD) is caused by Neisseria meningitidis, a gram-negative bacterium
Serogroup B is the leading cause of IMD, and diseases of serogroup W-135 and Y have stabilized at relatively lower incidence rates
This report is based on IMD data extracted from Enhanced Invasive Meningococcal Disease Surveillance System (eIMDSS), with disease onset between January 1, 2006, and December 31, 2011
Summary
Invasive meningococcal disease (IMD) is caused by Neisseria meningitidis, a gram-negative bacterium. IMD has been nationally notifiable in Canada since 1924 [3] through the Canadian Notifiable Diseases Surveillance System, which provides only basic epidemiological data. The Enhanced Invasive Meningococcal Disease Surveillance System (eIMDSS) was established in 1992 in Canada, capturing epidemiological and laboratory-linked data. From 2002 to 2005, when only some Canadian jurisdictions had implemented MenC programs, the incidence of serogroup C disease decreased by 43% compared with the period of 1995-2001 [8]. The last surveillance report published by the Agency described IMD in Canada from 2004 to 2005 [8]. The following report describes the epidemiology of IMD in Canada from January 1, 2006, to December 31, 2011
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