Epidemiology of Invasive Meningococcal Disease in Estonia
Published: 16.08.12 Updated: 11.12.2012 14:45:07
N. Kerbo1, J. Epstein
Department of Communicable Diseases Surveillance and Control, Health Board, Estonia
Citation: Kerbo N., Epstein E. Epidemiology of Invasive Meningococcal Disease in Estonia. EpiNorth 2012;13:5-7.
Invasive meningococcal infection has been a notifiable disease in Estonia since 1965. During the past decade, the incidence of invasive meningococcal disease reported in Estonia remained stable (0.1– 1.0 cases per 100,000 population per year). Neisseria meningitidis serogroup B constitute the most common serogroup causing disease in Estonia.
Invasive meningococcal disease is a contagious and life threatening infection caused by Neisseria meningitidis, a pathogen with the ability to cause clusters and epidemics. Invasive meningococcal disease remains an important public health concern in many European countries. The aim of the study was to determine the incidence and trends of invasive meningococcal disease in Estonia during 2001-2010.
Materials and Methods
Cases of invasive meningococcal disease reported to the Estonian Communicable Disease Registry (1, 2) were included in the study. The data were analyzed using descriptive methods.
The existing countrywide (universal), mandatory, passive surveillance system (clinical and laboratory) has adopted EU case definitions and ICD 10 code. One of the objectives of the meningococcal disease surveillance is to monitor circulating strains in order to indentify serogroup replacement. There is no reference laboratory for meningococcal disease in Estonia.
Meningococcal infection with the predominance of serogroup B has a low incidence in Estonia. During 2001-2010 the proportion of serogroup B was 65% while 10% were serogroup C, 14% serogroup A and 1% other serogroups. A significant decline of meningococcal infection morbidity has been observed during the last 10 years (Figure 1). In 2010 the morbidity rate was 0.1 cases per 100,000 population. A total of 103 invasive meningococcal infection cases that were confirmed by clinical diagnosis and laboratory analyses were notified in 2001-2010. All cases were reported as unvaccinated. Meningococcal infection has no variation in rates of incidence and serogroup distribution in the different part of Estonia.
During 2001-2010 there were 11 deaths due to the invasive meningococcal disease. Serogroup B was the main etiological agent. The case fatality rate varied from 0 to 36.4% in the last decade; no fatal cases were registered in 2002, 2003 and 2010. The average age of fatal cases was 39.5 years while 2 cases (18.2%) were children.
The clinical presentation included meningitis (56%), meningococcal septicaemia (39%), meningococcal encephalitis (1%) and other forms (4%) (Table 1).
Males and females were almost equally affected, with a male to female ratio of 1.6. The gender distribution remained relatively constant. The majority of cases (48.5%) were registered among 0-14 year old children, 8.7% among children below 1 year of age and 22.5% among persons aged 50 years and over (Figure 2). Nearly all cases (92%) from 2001-2006 were laboratory confirmed by culture. From 2007 all cases were laboratory confirmed either by culture or PCR. Seasonal variation of meningococcal infection was observed with most cases registered in winter and spring.
During the study period a total of 5 (4.8%) cases were imported. The infections probably originated in Finland (2 cases), Latvia (1 case) and 2 cases were reported to be acquired outside of the EU in Norway (1 case) and Russia (1 case). The rate of imported cases has decreased from 36.4% in 2004 to 8% in 2005. From 2006 all cases have been of domestic origin.
Currently, vaccination against meningococcal infection is not included in the national immunisation schedule. Vaccination is recommended for travellers to endemic countries and persons from risk groups including immunodeficient individuals with (asplenia, splenic dysfunction and others) with a predisposition to meningococcal infection.
Between 2001 and 2010 a total of 3625 persons were immunised against meningococcal infection. The majority (89.5%) were adults. The vaccination coverage is less than 0.3% and does not have an effect on the morbidity of meningococcal disease.
Estonia is one of the European countries with a low incidence of invasive meningococcal disease, between 0.1 and 1.0 cases per 100,000 population. Our study demonstrates that meningococci of serogroup B prevail; approximately two thirds of the cases were due to serogroup B. The majority of cases were among children and most of the infections were of a sporadic nature.
One of the objectives of the meningococcal disease surveillance in Estonia is to monitor circulating N. meningitidis serogroups. In the future, changes in phenotype and genotype of the more commonly observed strains will be detected and monitored. Molecular methods will be established to improve laboratory diagnostics and support epidemiological investigation in the future.
In order to achieve the objectives of surveillance and to provide comprehensive information on strains with high epidemic potential there is a need to improve laboratory capacities. Molecular typing of N. meningitidis is needed to better define the epidemiology of invasive meningococcal disease in Estonia.
1. Estonian Communicable Disease Registry (NAKIS). Health Board 2011.
2. Communicable Disease Statistics in Estonia. Part 14. Health Protection Inspectorate. Tallinn, 2008.