The meningococcus colonises the respiratory tract of up to 20% of the population without causing any symptoms, a phenomenon called meningococcal carriage. For every case of meningococcal disease there are usually several hundred carriers. Thus, studies of the epidemiology of meningococcal infection, and the effectiveness of a vaccine against this infection, should include the study of meningococcal carriage as well as of patients with meningococcal meningitis or septicaemia.
While many studies of carriage have been done in industrialised countries, few have been conducted in countries of the African meningitis belt and most of these were undertaken many years ago when techniques for characterising meningococci were limited.
What do existing studies show?
Studies of meningococcal carriage undertaken in industrialised countries have shown variations in the pattern of carriage by place, age and time and have identified important risk factors for carriage. For example in the UK, a large study identified smoking, kissing and attending night clubs as important risk factors for carriage in young adults. Very high carriage rates may occur in closed communities such as military camps.
A review of the limited number of studies of meningococcal carriage that have been undertaken in countries of the African meningitis belt showed very different patterns of carriage; carriage was generally most prevalent in older school children and in young adults. Carriage varied little by season.
Little is known about the rate of acquisition or loss of carriage in African populations or about the interaction in the pharynx between potentially pathogenic meningococci and other species of Neisseria that do not cause disease.