ARCHIVED - Guidelines for the Prevention and Control of Meningococcal Disease
3.0 Epidemiology of Invasive Meningococcal Disease in Canada
Updates on the epidemiology of IMD are published periodically in the Canada Communicable Disease Report (CCDR) and in the National Advisory Committee on Immunization (NACI) meningococcal vaccine statements. The most recent report was published in February 2004(2). Readers are referred to these reports for more detailed information.
Meningococcal disease is endemic in Canada, periods of increased activity occurring roughly every 10 to 15 years with no consistent pattern. The incidence rate of meningococcal disease has varied considerably with different serogroups, age groups, geographic locations and time. The last major epidemic, due to serogroup A, occurred in 1940-1943, when the peak incidence rate was close to 13 per 100,000 population per year. Since then the overall incidence of disease has remained at or below 2 per 100,000 per year (range 0.5 to 2.1)(2-5). There were sporadic localized outbreaks and periods of elevated incidence of serogroup C disease during 1989-1993 and 1999-2001(2,3). Immunization campaigns using serogroup C polysaccharide and conjugate vaccines were implemented in some regions during that period.
Case-by-case data for IMD in Canada are available from 1985 to 2001. During this period, an average of 305 cases of meningococcal disease were reported annually. Overall, the incidence rate has been highest among children <= 1 year of age, and then it declines as age increases except for a smaller peak in the 15- to 19-year age group. Disease occurs year round, but there is seasonal variation with the majority of cases occurring in the winter months.
Of the small numbers of isolates characterized from 1971 to 1974, Neisseria meningitidis serogroups A and C were most frequently identified(6). From 1975 to 1989, serogroup B predominated. The majority were serotype 2b, 4 and 15, and the most common subtype was P1.2(7). In 1986, a new clone of serogroup C, serotype 2a characterized by multilocus enzyme electrophoresis (MLEE) as electrophoretic type 15 (ET-15), was identified in Canada for the first time(7). Since then serogroups B and C have been responsible for most of the cases of endemic disease in Canada. Serogroup C isolates have almost exclusively been responsible for outbreaks in schools and communities. In addition, IMD caused by serogroup C has had a higher case fatality ratio and a greater incidence among adolescents than disease caused by serogroup B.
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