Project leader: Dr. S. Bertrand, Dr. W. Mattheus and R. Vanhoof
Neisseria meningitidis or meningococcus is a gram-negative diplococcus that colonizes the mucosal surfaces of nasopharynx and is transmitted through direct contact with respiratory secretions of infected persons, more often from asymptomatic carriers than patients. The human nasopharynx is the natural habitat of the meningococcus and meningococcal colonisation is not itself dangerous: between 5 and 25% of the population carry meningococci on their throats in the absence of disease (healthy carriers). However, in some cases, the meningococcal acquisition is followed by the development of invasive disease.
Neisseria meningitidis causes two types of severe illness: acute purulent meningitis and less commonly meningococcal septicaemia. Occasionally, meningococcal infection may be present as septic arthritis, pericarditis, pneumonia, conjunctivitis or pelvic infection. With Streptococcus pneumoniae and Haemophilus influenzae, Neisseria meningitidis is responsible for most cases of bacterial meningitis.
The most frequent symptoms are fever, headache, vomiting, stiff neck, confusion or coma for meningitis and fever, petechial rash or purpuric lesions and shock for meningococcal septicaemia. Meningococcal disease can progress very rapidly and is fatal at a rate of 10%. Of patients who recover, 10% have permanent hearing loss or other serious sequelae. The earlier the treatment (antibiotics) is given the better the prospect of recovery. Oral antibiotics are also recommended for close contacts of a case in order to prevent further spread.
Meningococcal disease is seasonal and occurs sporadically or in outbreaks and in epidemics. Most cases are seen in children under five years. A high incidence in teenagers between 15 and 19 years is also observed.
Neisseria meningitidis is an encapsulated bacterium and is classified into 12 serogroups based on the immunological reactivity of the capsular polysaccharide. The most common serogroups causing disease are A, B, C and less frequently Y and W135. Serogroup A accounts for most meningococcal disease cases in Africa and some parts of Asia; serogroups B and C are responsible for most meningococcal disease in the Americas and Europe. Serogroup Y infections are increasing in the United States and outbreaks caused by serogroup W135 occurred in Saudi Arabia and West Africa in 2000-2002.
Vaccines are available against serogroup A, C, Y and W135 diseases.
Meningococcal disease remains an important public health problem in both developing and industrialized countries. Surveillance is needed to detect and control outbreaks and epidemics.
In Belgium the surveillance of meningococcal disease is based on two sources of data
- the mandatory notification to the regional health authorities
- the Belgian Meningococcal Reference Centre that receives and characterizes isolates from peripheral laboratories since 1971 and gives valuable information about recent trends in the disease (see reports).
In Belgium, the last epidemic wave (caused by N. meningitidis B: 2b: P1.2) rose to its peak in 1971 and 1972, with a rate of 5 cases per 100 000 population. It was followed by a decrease of the number of cases to normal inter-epidemic proportions of one case per 100 000 inhabitants. However, since the beginning of the 1990s, an increase in incidence of meningococcal disease has been observed. The incidence calculated from the submission of meningococcal isolates to the Reference Centre has gradually increased from 1 to 3,7 cases per 100 000 population between 1991 and 2001. Until 1996 this increase in incidence was closely associated with serogroup B meningococci (B:4:P1.4). Since 1997, an increasing number of cases due to serogroup C strains was observed and in 2001, the serogroup C became predominant (49%). This increase was associated with phenotypes C:2a:P1.2,5, C:2a:P1.5 and C:2a:P1.2 belonging to the virulent ST-11/ET-37 clonal complex. In an attempt to control this outbreak, immunization campaigns using conjugate meningococcal C vaccines and focusing on 1-5 year olds were launched in November 2001 in Flanders and in March 2002 in Wallonia. The campaign in Wallonia ended in September 2002 but the Flanders program was extended to additional age groups to cover the entire 1-18 years cohort before the end of 2004. One year after the start of the immunization campaign a global decrease by 50% in meningococcal C disease and a fall of the number of fatal serogroup C infections (22 in 2001, 8 in 2002) were registered. The decrease was observed in all age groups: 48% in the age group 0-19 years and 46% among adults above 20 years (not targeted by the vaccination). In 2004, serogroup C represented only 11% of all cases and the national incidence rate of meningococcal disease has fallen to 1,5/100 000 .