Epidemiology of Neisseria meningitidis; prevalence and symptoms from the upper respiratory tract in family members to patients with meningococcal disease.

The prevalence of Neisseria meningitidis during endemic conditions was studied in 2 groups of people: (1) 64 family members to patients with meningococcal disease, and (2) 64 family members to patients with meningitis due to Haemophilus influenzae or Streptococcus pneumoniae. In group 1 the carrier rate of meningococci of the same serogroup, sensitivity to sulphonamide, and serotype (group B) as the index strain was 34%. The carrier rate of meningococci group A, B, C and Y was 39% in group 1 and 1.6% in group 2. The 25 times higher carrier rate in group 1 gives some explanation of the increased risk for family members to patients with meningococcal disease. This risk was calculated to have been 3,000-4,000 times higher for the family members during one month after the diagnosis of an index case 1965-1977 in our county. The hypothesis that meningococci as a rule are introduced into a family by an adult and then spread within the family to a child finds no support in the present study. A statistically highly significant association was found between carriage of pathogenic meningococci and symptoms from the upper respiratory tract.