Meningococcal carriage in relation to an outbreak of invasive disease due to Neisseria meningitidis serogroup C in the Netherlands

Background: a cross-sectional study on meningococcal carriage was performed in Putten, a small rural town in the Netherlands where an unusual high inc idence of invasive meningococcal disease (IMD) due to Neisseria meningitidi s C:2a:P1.5 occurred. The outbreak was controlled by mass vaccination of al l inhabitants aged 2 to 20 years, Methods: meningococcal carriage was studied in three groups: (1) a systemat ic age-specific sample of 2-20 year olds who visited the immunization clini c in Putten (January 1998; n = 411): (2) children and adolescents in the sa me age range recruited through a kindergarten and schools in Venlo, a town where the causative strain of IMD had not been encountered (February 1998; n = 374); (3) all initial carriers in Putten and a sample of non-carriers i n that town (March 1998; n = 145). Oropharyngeal swabs were taken for the p urpose of isolating N.meningitidis. Results: the prevalence of carriage was 12.4% in Putten and 18.2% in Venlo, but the prevalence of group C meningococci was higher in Putten (1.7%) tha n Venlo (0.5%), N. meningitidis C:2a:P1.5 was isolated twice in Putten and not at all in Venlo. A second examination in Putten showed that 18 of the 2 2 repeatedly tested carriers were still carriers, and sis new carriers were found among the 55 initial nan-carriers, Of the two known carriers of C:2a :P1.5, one was still carrying the same strain. and the other did not partic ipate in the second investigation. Carriage was associated with increasing family size, discotheque visits and visits to youth clubs and sports clubs, In contrast, visits to the swimming pool appeared to be related to a lower risk, as was recent antibiotic use. Conclusion: the prevalence of carriage with the invasive strain C:2a:P1.5 w as low in the population that experienced a community-wide outbreak recentl y; the specific strain was not found in the reference population. This indi cates a relatively high risk of developing the invasive disease for those w ho became infected with such strains.