Longitudinal study of asymptomatic meningococcal carriage in two Belgian populations of schoolchildren.

In Brussels, a 15-month longitudinal survey was conducted in two primary schools, from March 1975 to May 1976, in order to analyse the dynamic of asymptomatic meningococcal carriage, during an epidemic mainly caused by serogroup B, serotype 2 Neisseria meningitidis. In the first school, which is situated in a suburban area with upper-middle socio-economic status of residents, a mean prevalence of carriers of 10 per cent, an acquisition rate of eight per 1000 months, and a mean duration of carriage of 12.4 months were observed among 158 schoolchildren aged six to 11 years old. In the second school, which is situated in a densely populated area with low socio-economic status of residents, a mean prevalence of carriers of 33 per cent, an acquisition rate of 28 per 1000 months, and a mean duration of carriage of 11.7 months were observed among 203 schoolchildren aged three to 14 years old. For both schools, the median duration of carriage was estimated at 9.4 months. The differences of prevalence and incidence of acquisition between the two schools cannot be explained by age, sex or ethnic factors and are probably related to socio familial variables. The theoretical relationship between prevalence, incidence and duration of meningococcal carriage was for the first time demonstrated in this study. The results also suggest that populations of low socio-economic status and living in densely populated areas constitute a target population for meningococcal disease prevention.

Validity of the recording of meningococcal disease according to various sources of information.

A study was made in Belgium in order to assess the completeness and specificity of the recording of meningococcal disease by routine sources of information. Ninety-three cases identified in a hospital survey were linked with those recorded in mortality statistics, in the notification of communicable diseases, and by the National Reference Laboratory for meningococci. Statistics based on mortality data appeared to be of low validity. The overall completeness of recording was 44% for the notification of communicable disease, and 40% for the reference laboratory. When these two sources were used for surveillance, the completeness of case-finding increased to 56%. When the analysis was restricted to bacteriologically-confirmed cases, the completeness of recording was 62% for the notification system, 70% for the laboratory, and 84% for both sources. The surveillance of communicable diseases should rely on various sources of information. Laboratory data should be systematically used in order to improve both the completeness of recording and the specificity of case-ascertainment.

[Methods for analyzing the frequency, prevalence and the duration of asymptomatic carriage of Neisseria meningitidis. Longitudinal study of a school population in Belgium]. / Méthodes pour l'analyse de l'incidence, la prévalence et la durée du portage asymptomatique de Neisseria meningitidis. Etude longitudinale dans une population scolaire en Belgique.

In Belgium, during an outbreak of meningococcal disease mainly due to serogroup B, serotype 2 meningococcus, a prospective study of asymptomatic carriage was undertaken in two primary schools. From march 1975 to may 1976, 361 schoolchildren aged 3 to 14 years were surveyed. The result of nasopharyngeal cultures were adjusted to compensate the lack of sensitivity and specificity of the identification techniques. The hypotheses on which the adjustment rules are based were statistically validated. The mean prevalence of meningococcal carriage was 23 p. 100, the incidence rate was 0.02 acquisition for month and for person. The median duration of carriage was estimated at 9.4 months, and the mean duration at 13.6 months. For the first time, the expected relationship between prevalence, incidence, and duration was confirmed for meningococcal carriage.

Pili of Neisseria meningitidis: an electron microscopic study on their occurrence, related to different strain characteristics.

The occurrence of pili has been assessed for 85 strains of Neisseria meningitidis belonging to different serogroups and serotypes, isolated from nasopharyngeal carriers and patients with acute disease. The evolution of piliation on multiple subcultivation has been followed for 16 strains. Almost all the strains were piliated, regardless of their origin, serogroup or serotype. Piliation was generally maintained, although to a variable extent, through more than 50 passages. Type, regulation and possible function in vivo of the described pili are discussed.